Patent Publication Number: US-2022229624-A1

Title: Screen projection method, system, and related apparatus

Description:
This application claims priority to Chinese Patent Application No. 201910459096.0, filed with the China National Intellectual Property Administration on May 29, 2019, and entitled “SCREEN PROJECTION METHOD, SYSTEM, AND RELATED APPARATUS”, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This application relates to the field of electronic technologies, and in particular, to a screen projection method, a system, and a related apparatus. 
     BACKGROUND 
     With the development of digital technologies, an electronic device such as a mobile phone is used as a personal computer (PC), and this is one of the important means to implement mobile office. Specifically, the electronic device such as the mobile phone may project, by using a Wi-Fi-display (Wi-Fi-Display) function or a Microsoft continuum function, display content on a screen of the mobile phone to a large-screen display of a PC or the like. 
     Currently, the screen of an electronic device such as a mobile phone has become increasingly larger. To give full play to application value of a large screen, a split-screen display technology is developed, so that an electronic device such as a mobile phone can simultaneously display a plurality of application interface windows on a same touchscreen. However, when the plurality of application interface windows are simultaneously split-screen displayed on the touchscreen of an electronic device such as a mobile phone, if the electronic device such as the mobile phone performs screen projection, the electronic device such as the mobile phone projects, onto a large-screen display for displaying, all the plurality of application interface windows split-screen displayed on the touchscreen. Therefore, some relatively private application interface windows (for example, a chat interface window of Messages) split-screen displayed on the electronic device such as the mobile phone are also projected onto the large-screen display. This easily causes loss of user privacy. 
     SUMMARY 
     This application provides a screen projection method, a system, and a related apparatus, so that when an electronic device split-screen displays a plurality of application interfaces, one or more of the plurality of application interfaces can be selected and projected onto a large-screen display, to ensure that an application interface involving user privacy is projected only after a user agrees and confirms. This protects user privacy and improves user experience. 
     According to a first aspect, this application provides a screen projection method, including: First, an electronic device displays M application interfaces on a display of the electronic device, where M is an integer greater than 1. Then, the electronic device receives a first selection operation, and determines N application interfaces based on the first selection operation, where the first selection operation is performed on the electronic device to determine the N application interfaces from the M application interfaces, and N is a positive integer less than or equal to M. Then, the electronic device sends first data to an external display device in response to the first selection operation, where the first data is used by the external display device to display the N application interfaces. 
     According to the screen projection method provided in this application, when a plurality of application interfaces are displayed on the display of the electronic device, the electronic device may receive a selection operation of a user, and project one or more application interfaces selected by the user onto the external display device for displaying. In this way, the electronic device can project, based on the selection operation of the user onto the external display device for displaying, the one or more application interfaces selected by the user on the display of the electronic device. This ensures that an application interface concerning user privacy is projected only after the user agrees and confirms, to ensure user privacy and improve user experience. 
     In a possible implementation, the first data includes a to-be-projected image including the N application interfaces. Before the electronic device sends the first data to the external display device, the electronic device may further obtain a synthesized image of the M application interfaces and first display information of the N application interfaces, where the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces. The electronic device crops the to-be-projected image from the synthesized image of the M application interfaces based on the first display information of the N application interfaces. In this way, the electronic device can project, onto the external display device, the N application interfaces of the M application interfaces split-screen displayed on the display. In this way, the electronic device can project, onto the external display device, the N application interfaces of the M application interfaces split-screen displayed on the display. 
     In a possible implementation, before the electronic device sends the first data to the external display device, the electronic device obtains a synthesized image of the M application interfaces and first display information of the N application interfaces. The first data includes the synthesized image of the M application interfaces and the first display information of the N application interfaces, the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces, and the first display information is used by the external display device to crop, from the synthesized image of the M application interfaces, an image including the N application interfaces and display the image. In this way, the electronic device can project, onto the external display device, the N application interfaces of the M application interfaces split-screen displayed on the display. 
     In a possible implementation, the first data includes respective image data streams of the N application interfaces, and is used by the external display device to display the N application interfaces in N display windows in a one-to-one correspondence. Before the electronic device sends the first data to the external display device, the electronic device may further obtain the respective image data streams of the N application interfaces. In this way, the electronic device can project, onto the external display device, the N application interfaces of the M application interfaces split-screen displayed on the display. 
     In a possible implementation, that the electronic device receives a first selection operation specifically includes: The electronic device receives a first input. In response to the first input, the electronic device displays M projection add controls on the display, where the M projection add controls one-to-one correspond to the M application interfaces. The electronic device receives a second input used by the user to trigger N of the M projection add controls. The electronic device determines, based on the second input, the N application interfaces selected by the user, and sends, to the external display device, the first data used to display the N application interfaces. In this way, a projection add control is triggered, so that an application interface corresponding to the projection add control is projected onto the external display device, to ensure that an application interface involving user privacy is projected only after the user agrees and confirms. This ensures user privacy. 
     In a possible implementation, in response to the first input, the electronic device may display M projection add controls and an OK button on the display. After receiving a second input used by the user to trigger N of the M projection add controls, the electronic device may further receive a third input used by the user to trigger the OK button, and determine, based on the second input, the N application interfaces selected by the user. In response to the third input, the electronic device may send, to the external display device, the first data used to display the N application interfaces. In this way, the user can be prevented from accidentally touching a projection add control, to prevent the user from mistakenly projecting an application interface corresponding to the projection add control onto the external display device for displaying. This improves user experience. 
     In a possible implementation, after any projection add control is triggered, the electronic device displays a projection cancel control corresponding to the projection add control, where the projection cancel control is used by the user to cancel projection of an application interface corresponding to the projection cancel control. The electronic device receives a fourth input used by the user to trigger the projection cancel control. In response to the fourth input, the electronic device stops sending, to the external display device, image data of the application interface corresponding to the projection cancel control. In this way, the electronic device can stop projection of an application interface onto the external display device at any time according to a user requirement, to improve user experience. 
     In a possible implementation, that the electronic device receives a first selection operation may specifically include: The electronic device receives a fifth input. In response to the fifth input, the electronic device displays a shortcut menu on the display, where the shortcut menu includes M options, and the M options one-to-one correspond to the M application interfaces. The electronic device receives a sixth input used to select N of the M options. The electronic device determines, based on the sixth input, the N application interfaces selected by a user, and sends, to the external display device, the first data used to display the N application interfaces. In this way, the electronic device can select, based on the input operation of the user, the one or more application interfaces from the plurality of application interfaces displayed on the display of the electronic device, and project the one or more application interfaces onto the external display device, to ensure that an application interface involving user privacy is projected only after the user selects the application interface. This ensures user privacy. 
     In a possible implementation, the shortcut menu may include the M options and an OK button. After the electronic device receives a sixth input used to select N of the M options, the electronic device may further receive a seventh input used by the user to trigger the OK button. The electronic device may determine, based on the sixth input, the N application interfaces selected by the user. In response to the seventh input, the electronic device sends, to the external display device, the first data used to display the N application interfaces. In this way, after the user selects the N options, the electronic device projects the N application interfaces corresponding to the N options onto the external display device for displaying only after the user confirms. This prevents the user from mistakenly selecting an application interface for projection, and ensures user privacy. 
     According to a second aspect, this application provides a system, including an electronic device and an external display device. The electronic device is connected to the external display device. The electronic device is configured to display M application interfaces on a display of the electronic device, where M is an integer greater than 1. The electronic device is further configured to receive a first selection operation, and determine N application interfaces based on the first selection operation, where the first selection operation is performed on the electronic device to select the N application interfaces from the M application interfaces, and N is a positive integer less than or equal to M. The electronic device is further configured to send first data to the external display device in response to the first selection operation. The external display device is configured to display the N application interfaces after receiving the first data. 
     According to a third aspect, this application provides an electronic device, including a memory, a display, and at least one processor. The memory stores program code. The memory, the display, and the at least one processor communicate with each other. The processor runs the code to indicate the electronic device to perform the screen projection method according to any possible implementation of the first aspect. 
     According to a fourth aspect, embodiments of this application provide a computer storage medium, including computer instructions. When the computer instructions are run on an electronic device, the electronic device is enabled to perform the screen projection method according to any possible implementation of the first aspect. 
     According to a fifth aspect, embodiments of this application provide a computer program product. When the computer program product is run on a computer, the computer is enabled to perform the screen projection method according to any possible implementation of the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a structure of an electronic device according to an embodiment of this application; 
         FIG. 2  is a schematic diagram of a software architecture according to an embodiment of this application; 
         FIG. 3  is a schematic diagram of a structure of a system according to an embodiment of this application; 
         FIG. 4A-1  and  FIG. 4A-2  to  FIG. 4J-1  and  FIG. 4J-2  are schematic diagrams of a group of interfaces according to an embodiment of this application; 
         FIG. 5A-1  and  FIG. 5A-2  to  FIG. 5F-1  and  FIG. 5F-2  are schematic diagrams of another group of interfaces according to an embodiment of this application; 
         FIG. 6A-1  and  FIG. 6A-2  to  FIG. 6H-1  and  FIG. 6H-2  are schematic diagrams of another group of interfaces according to an embodiment of this application; 
         FIG. 7A-1  and  FIG. 7A-2  to  FIG. 7G-1  and  FIG. 7G-2  are schematic diagrams of another group of interfaces according to an embodiment of this application; 
         FIG. 8A-1  and  FIG. 8A-2  to  FIG. 8E-1  and  FIG. 8E-2  are schematic diagrams of another group of interfaces according to an embodiment of this application; 
         FIG. 9A-1 ,  FIG. 9A-2 ,  FIG. 9B-1 , and  FIG. 9B-2  are schematic diagrams of another group of interfaces according to an embodiment of this application; 
         FIG. 10  is a schematic flowchart of a screen projection method in the conventional technology; 
         FIG. 11  is a schematic flowchart of a screen projection method according to an embodiment of this application; 
         FIG. 12  is a schematic flowchart of a screen projection method according to another embodiment of this application; 
         FIG. 13  is a schematic flowchart of a screen projection method according to another embodiment of this application; and 
         FIG. 14  is a schematic flowchart of a screen projection method according to another embodiment of this application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly describes technical solutions in the embodiments of this application in detail with reference to accompanying drawings. In the descriptions of the embodiments of this application, unless otherwise specified, “/” indicates “or”. For example, A/B may indicate A or B. The term “and/or” in this specification merely describes an association relationship for describing associated objects, and indicates that three relationships may exist. For example, A and/or B may indicate the following three cases: Only A exists, both A and B exist, and only B exists. In addition, in the descriptions of the embodiments of this application, “a plurality of” means two or more. 
     The following terms “first” and “second” are merely intended for description, and shall not be understood as an indication or implication of relative importance or implicit indication of a quantity of indicated technical features. Therefore, a feature limited by “first” or “second” may explicitly or implicitly include one or more features. In the descriptions of the embodiments of this application, unless otherwise specified, “a plurality of” means two or more. 
       FIG. 1  is a schematic diagram of a structure of an electronic device  100 . 
     The following uses the electronic device  100  as an example to specifically describe this embodiment. It should be understood that the electronic device  100  shown in  FIG. 1  is merely an example, and the electronic device  100  may have more or fewer components than those shown in  FIG. 1 , or two or more components may be combined, or different component configurations may be used. Various components shown in the figure may be implemented in hardware, software, or a combination of hardware and software that includes one or more signal processing and/or application-specific integrated circuits. 
     The electronic device  100  may include a processor  110 , an external memory interface  120 , an internal memory  121 , a universal serial bus (universal serial bus, USB) interface  130 , a charging management module  140 , a power management module  141 , a battery  142 , an antenna  1 , an antenna  2 , a mobile communications module  150 , a wireless communications module  160 , an audio module  170 , a speaker  170 A, a receiver  170 B, a microphone  170 C, a headset jack  170 D, a sensor module  180 , a button  190 , a motor  191 , an indicator  192 , a camera  193 , a display  194 , a subscriber identification module (subscriber identification module, SIM) card interface  195 , and the like. The sensor module  180  may include a pressure sensor  180 A, a gyro sensor  180 B, a barometric pressure sensor  180 C, a magnetic sensor  180 D, an acceleration sensor  180 E, a distance sensor  180 F, an optical proximity sensor  180 G, a fingerprint sensor  180 H, a temperature sensor  180 J, a touch sensor  180 K, an ambient light sensor  180 L, a bone conduction sensor  180 M, and the like. 
     It may be understood that a structure shown in the embodiments of the present invention does not constitute a specific limitation on the electronic device  100 . In some other embodiments of this application, the electronic device  100  may include more or fewer components than those shown in the figure, or some components may be combined, or some components may be split, or different component arrangements may be used. The components in the figure may be implemented by hardware, software, or a combination of software and hardware. 
     The processor  110  may include one or more processing units. For example, the processor  110  may include an application processor (AP), a modem processor, a graphics processing unit (GPU), an image signal processor (ISP), a controller, a memory, a video codec, a digital signal processor (DSP), a baseband processor, and/or a neural-network processing unit (NPU). Different processing units may be independent components, or may be integrated into one or more processors. 
     The controller may be a nerve center and a command center of the electronic device  100 . The controller may generate an operation control signal based on an instruction operation code and a time sequence signal, to control to read instructions and execute instructions. 
     A memory may be further disposed in the processor  110 , and is configured to store instructions and data. In some embodiments, the memory in the processor  110  is a cache memory. The memory may store instructions or data that has just been used or is cyclically used by the processor  110 . If the processor  110  needs to use the instructions or the data again, the processor  110  may directly invoke the instructions or the data from the memory, to avoid repeated access. This reduces a waiting time of the processor  110 , and improves system efficiency. 
     In some embodiments, the processor  110  may include one or more interfaces. The interface may include an inter-integrated circuit (I2C) interface, an inter-integrated circuit sound (I2S) interface, a pulse code modulation (PCM) interface, a universal asynchronous receiver/transmitter (UART) interface, a mobile industry processor interface (MIPI), a general-purpose input/output (GPIO) interface, a subscriber identity module (SIM) interface, a universal serial bus (USB) interface, and/or the like. 
     The I2C interface is a two-way synchronization serial bus, and includes a serial data line (SDL) and a serial clock line (SCL). In some embodiments, the processor  110  may include a plurality of groups of I2C buses. The processor  110  may be separately coupled to the touch sensor  180 K, a charger, a flash, the camera  193 , and the like through different I2C bus interfaces. For example, the processor  110  may be coupled to the touch sensor  180 K through the I2C interface, so that the processor  110  communicates with the touch sensor  180 K through the I2C bus interface, to implement a touch function of the electronic device  100 . 
     The I2S interface may be used for audio communication. In some embodiments, the processor  110  may include a plurality of groups of I2S buses. The processor  110  may be coupled to the audio module  170  through an I2S bus, to implement communication between the processor  110  and the audio module  170 . In some embodiments, the audio module  170  may transmit an audio signal to the wireless communications module  160  through the I2S interface, to implement a function of answering a call by using a Bluetooth headset. 
     The PCM interface may also be configured to perform audio communication, and sample, quantize, and code an analog signal. In some embodiments, the audio module  170  may be coupled to the wireless communications module  160  through the PCM bus interface. In some embodiments, the audio module  170  may alternatively transmit an audio signal to the wireless communications module  160  through the PCM interface, to implement a function of answering a call by using a Bluetooth headset. Both the I2S interface and the PCM interface may be configured to perform audio communication. 
     The UART interface is a universal serial data bus, and is configured to perform asynchronous communication. The bus may be a two-way communications bus. The bus converts to-be-transmitted data between serial communication and parallel communication. In some embodiments, the UART interface is usually configured to connect the processor  110  to the wireless communications module  160 . For example, the processor  110  communicates with a Bluetooth module in the wireless communications module  160  through the UART interface, to implement a Bluetooth function. In some embodiments, the audio module  170  may transmit an audio signal to the wireless communications module  160  through the UART interface, to implement a function of playing music by using the Bluetooth headset. 
     The MIPI interface may be configured to connect the processor  110  to a peripheral component such as the display  194  or the camera  193 . The MIPI interface includes a camera serial interface (CSI), a display serial interface (DSI), and the like. In some embodiments, the processor  110  communicates with the camera  193  through the CSI interface, to implement a shooting function of the electronic device  100 . The processor  110  communicates with the display  194  through the DSI interface, to implement a display function of the electronic device  100 . 
     The GPIO interface may be configured by software. The GPIO interface may be configured as a control signal or a data signal. In some embodiments, the GPIO interface may be configured to connect the processor  110  to the camera  193 , the display  194 , the wireless communications module  160 , the audio module  170 , the sensor module  180 , and the like. The GPIO interface may alternatively be configured as the I2C interface, the I2S interface, the UART interface, the MIPI interface, or the like. 
     The USB interface  130  is an interface that complies with a USB standard specification, and may be specifically a mini USB interface, a micro USB interface, a USB Type-C interface, or the like. The USB interface  130  may be configured to connect to the charger to charge the electronic device  100 , or may be configured to transmit data between the electronic device  100  and a peripheral device, or may be configured to connect to a headset to play audio by using the headset, or may be configured to connect to another electronic device such as an AR device. 
     It can be understood that an interface connection relationship between the modules shown in the embodiments of the present invention is merely an example for description, and does not constitute a limitation on the structure of the electronic device  100 . In some other embodiments of this application, the electronic device  100  may alternatively use an interface connection manner that is different from that in the foregoing embodiment, or a combination of a plurality of interface connection manners. 
     The charging management module  140  is configured to receive a charging input from the charger. The charger may be a wireless charger or a wired charger. In some embodiments in which wired charging is used, the charging management module  140  may receive a charging input from the wired charger through the USB interface  130 . In some embodiments in which wireless charging is used, the charging management module  140  may receive a wireless charging input through a wireless charging coil of the electronic device  100 . The charging management module  140  may further supply power to the electronic device by using the power management module  141  while charging the battery  142 . 
     The power management module  141  is configured to connect to the battery  142  and the charging management module  140  to the processor  110 . The power management module  141  receives an input from the battery  142  and/or the charging management module  140 , and supplies power to the processor  110 , the internal memory  121 , an external memory, the display  194 , the camera  193 , the wireless communications module  160 , and the like. The power management module  141  may be further configured to monitor parameters such as battery power, a battery cycle count, and a battery health status (electric leakage or impedance). In some other embodiments, the power management module  141  may alternatively be disposed in the processor  110 . In some other embodiments, the power management module  141  and the charging management module  140  may alternatively be disposed in a same device. 
     A wireless communication function of the electronic device  100  may be implemented by using the antenna  1 , the antenna  2 , the mobile communications module  150 , the wireless communications module  160 , the modem processor, the baseband processor, and the like. 
     The antenna  1  and the antenna  2  each are configured to transmit and receive electromagnetic wave signals. Each antenna in the electronic device  100  may be configured to cover one or more communications frequency bands. Different antennas may be further multiplexed to improve antenna utilization. For example, the antenna  1  may be multiplexed as a diversity antenna in a wireless local area network. In some other embodiments, an antenna may be used in combination with a tuning switch. 
     The mobile communications module  150  may provide a solution that is for wireless communication including 2G/3G/4G/5G and the like and that is applied to the electronic device  100 . The mobile communications module  150  may include at least one filter, a switch, a power amplifier, a low noise amplifier (LNA), and the like. The mobile communications module  150  may receive an electromagnetic wave through the antenna  1 , perform processing such as filtering or amplification on the received electromagnetic wave, and transmit a processed electromagnetic wave to the modem processor for demodulation. The mobile communications module  150  may further amplify a signal modulated by the modem processor, and convert the signal into an electromagnetic wave for radiation through the antenna  1 . In some embodiments, at least some function modules of the mobile communications module  150  may be disposed in the processor  110 . In some embodiments, at least some function modules of the mobile communications module  150  and at least some modules of the processor  110  may be disposed in a same device. 
     The modem processor may include a modulator and a demodulator. The modulator is configured to modulate a to-be-sent low-frequency baseband signal into a medium or high-frequency signal. The demodulator is configured to demodulate a received electromagnetic wave signal into a low-frequency baseband signal. Then, the demodulator transmits the low-frequency baseband signal obtained through the demodulation to the baseband processor for processing. The low-frequency baseband signal is processed by the baseband processor, and then transmitted to the application processor. The application processor outputs a sound signal by using an audio device (not limited to the speaker  170 A, the receiver  170 B, and the like), or displays an image or a video by using the display  194 . In some embodiments, the modem processor may be an independent component. In some other embodiments, the modem processor may be independent of the processor  110 , and is disposed in a same device as the mobile communications module  150  or another function module. 
     The wireless communications module  160  may provide a wireless communication solution that includes a wireless local area network (WLAN) (for example, a wireless fidelity (Wi-Fi) network), Bluetooth (BT), a global navigation satellite system (GNSS), frequency modulation (FM), a near field communication (NFC) technology, an infrared (IR) technology, or the like and that is applied to the electronic device  100 . The wireless communications module  160  may be one or more devices that integrate at least one communication processing module. The wireless communications module  160  receives an electromagnetic wave through the antenna  2 , performs frequency modulation and filtering processing on an electromagnetic wave signal, and sends a processed signal to the processor  110 . The wireless communications module  160  may further receive a to-be-sent signal from the processor  110 , perform frequency modulation and amplification on the signal, and convert the signal into an electromagnetic wave for radiation through the antenna  2 . 
     In some embodiments, in the electronic device  100 , the antenna  1  is coupled to the mobile communications module  150 , and the antenna  2  is coupled to the wireless communications module  160 , so that the electronic device  100  can communicate with a network and another device by using a wireless communications technology. The wireless communications technology may include a global system for mobile communications (GSM), a general packet radio service (GPRS), code division multiple access (CDMA), wideband code division multiple access (WCDMA), time-division code division multiple access (TD-SCDMA), long term evolution (LTE), BT, a GNSS, a WLAN, NFC, FM, an IR technology, and/or the like. The GNSS may include a global positioning system (GPS), a global navigation satellite system (GLONASS), a BeiDou navigation satellite system (BDS), a quasi-zenith satellite system (QZSS), and/or satellite based augmentation systems (SBAS). 
     The electronic device  100  implements a display function by using the GPU, the display  194 , the application processor, and the like. The GPU is a microprocessor for image processing, and is connected to the display  194  and the application processor. The GPU is configured to perform mathematical and geometric calculation, and is used for graphics rendering. The processor  110  may include one or more GPUs that execute a program instruction to generate or change display information. 
     The display  194  is configured to display an image, a video, and the like. The display  194  includes a display panel. The display panel may use a liquid crystal display (LCD), an organic light-emitting diode (OLED), an active-matrix organic light emitting diode or an active-matrix organic light emitting diode (AMOLED), a flexible light-emitting diode (FLED), a mini-LED, a micro-LED, a micro-OLED, a quantum dot light emitting diode (QLED), or the like. In some embodiments, the electronic device  100  may include one or N displays  194 , where N is a positive integer greater than 1. 
     The electronic device  100  may implement a shooting function through the ISP, the camera  193 , the video codec, the GPU, the display  194 , the application processor, and the like. 
     The ISP is configured to process data fed back by the camera  193 . For example, during shooting, a shutter is pressed, and light is transmitted to a photosensitive element of the camera through a lens. The photosensitive element of the camera converts an optical signal into an electrical signal, and transmits the electrical signal to the ISP for processing. The ISP converts the electrical signal into an image that is perceptible to the eye. The ISP may further perform algorithm optimization on noise, brightness, and complexion of the image. The ISP may further optimize parameters such as exposure and color temperature of a shooting scene. In some embodiments, the ISP may be disposed in the camera  193 . 
     The camera  193  is configured to capture a static image or a video. An optical image of an object is generated through the lens, and is projected onto the photosensitive element. The photosensitive element may be a charge coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) phototransistor. The photosensitive element converts an optical signal into an electrical signal, and then transmits the electrical signal to the ISP to convert the electrical signal into a digital image signal. The ISP outputs the digital image signal to the DSP for processing. The DSP converts the digital image signal into a standard image signal in an RGB format, a YUV format, or the like. In some embodiments, the electronic device  100  may include one or N cameras  193 , where N is a positive integer greater than 1. 
     The digital signal processor is configured to process a digital signal, and may process another digital signal in addition to the digital image signal. For example, when the electronic device  100  selects a frequency, the digital signal processor is configured to perform Fourier transform on frequency energy and the like. 
     The video codec is configured to compress or decompress a digital video. The electronic device  100  may support one or more video codecs. Therefore, the electronic device  100  may play or record videos in a plurality of encoding formats, for example, MPEG (moving picture experts group, MPEG)-1, MPEG-2, MPEG-3, and MPEG-4. 
     The NPU is a neural-network (NN) computing processor. The NPU quickly processes input information by referring to a biological neural network structure, for example, by referring to a mode of transfer between human brain neurons, and may further continuously perform self-learning. The electronic device  100  may implement intelligent cognition such as image recognition, facial recognition, speech recognition, and text understanding through the NPU. 
     The external memory interface  120  may be configured to connect to an external memory card such as a micro SD card, to extend a storage capability of the electronic device  100 . The external storage card communicates with the processor  110  through the external memory interface  120 , to implement a data storage function, for example, to store files such as music and a video in the external memory card. 
     The internal memory  121  may be configured to store computer-executable program code. The executable program code includes instructions. The processor  110  runs the instructions stored in the internal memory  121  to perform various function applications of the electronic device  100  and process data. The internal memory  121  may include a program storage area and a data storage area. The program storage area may store an operating system, an application required by at least one function (for example, a sound playing function and an image playing function), and the like. The data storage area may store data (for example, audio data, a phone book, and the like) created in a process of using the electronic device  100 , and the like. In addition, the internal memory  121  may include a high-speed random access memory, or may include a nonvolatile memory, for example, at least one magnetic disk storage device, a flash memory device, or a universal flash storage (universal flash storage, UFS). 
     The electronic device  100  may implement audio functions, for example, music playing and recording, by using the audio module  170 , the speaker  170 A, the receiver  170 B, the microphone  170 C, the headset jack  170 D, the application processor, and the like. 
     The audio module  170  is configured to convert digital audio information into an analog audio signal for output, and is also configured to convert an analog audio input into a digital audio signal. The audio module  170  may be further configured to perform audio signal encoding and decoding. In some embodiments, the audio module  170  may be disposed in the processor  110 , or some function modules of the audio module  170  are disposed in the processor  110 . 
     The speaker  170 A, also referred to as a “horn”, is configured to convert an audio electrical signal into a sound signal. The electronic device  100  may listen to music or answer a hands-free call by using the speaker  170 A. 
     The receiver  170 B, also referred to as an “earpiece”, is configured to convert an audio electrical signal into a sound signal. When the electronic device  100  answers a call or receives voice information, the receiver  170 B may be placed near a human ear to listen to a voice. 
     The microphone  170 C, also referred to as a “mike” or a “microphone”, is configured to convert a sound signal into an electrical signal. When making a call or sending a voice message, a user may make a sound near the microphone  170 C, to input a sound signal to the microphone  170 C. At least one microphone  170 C may be disposed in the electronic device  100 . In some other embodiments, two microphones  170 C may be disposed in the electronic device  100 , to collect a sound signal and implement a noise reduction function. In some other embodiments, three, four, or more microphones  170 C may alternatively be disposed in the electronic device  100 , to collect a sound signal, implement noise reduction, and identify a sound source, to implement a directional recording function and the like. 
     The headset jack  170 D is configured to connect to a wired headset. The headset jack  170 D may be the USB interface  130  or a  3 . 5  mm open mobile terminal platform (OMTP) standard interface or a cellular telecommunications industry association of the USA (CTIA) standard interface. 
     The pressure sensor  180 A is configured to sense a pressure signal, and can convert the pressure signal into an electrical signal. In some embodiments, the pressure sensor  180 A may be disposed on the display  194 . There are many types of pressure sensors  180 A such as a resistive pressure sensor, an inductive pressure sensor, and a capacitive pressure sensor. The capacitive pressure sensor may include at least two parallel plates made of conductive materials. Capacitance between electrodes changes when force is applied to the pressure sensor  180 A. The electronic device  100  determines pressure intensity based on a change of the capacitance. When a touch operation is performed on the display  194 , the electronic device  100  detects a strength of the touch operation based on the pressure sensor  180 A. The electronic device  100  may also calculate a touch location based on a detection signal of the pressure sensor  180 A. In some embodiments, touch operations that are performed at a same touch location but have different touch operation intensity may correspond to different operation instructions. For example, when a touch operation whose touch operation intensity is less than a first pressure threshold is performed on an icon of Messages, an instruction for viewing an SMS message is executed. When a touch operation whose touch operation intensity is greater than or equal to the first pressure threshold is performed on an icon of Messages, an instruction for creating an SMS message is executed. 
     The gyro sensor  180 B may be configured to determine a motion posture of the electronic device  100 . In some embodiments, an angular velocity of the electronic device  100  around three axes (namely, axes x, y, and z) may be determined by using the gyro sensor  180 B. The gyro sensor  180 B may be configured to perform image stabilization during photographing. For example, when the shutter is pressed, the gyro sensor  180 B detects an angle at which the electronic device  100  jitters, and calculates, based on the angle, a distance for which a lens module needs to compensate, and allows the lens to eliminate the jitter of the electronic device  100  through a reverse motion, to implement image stabilization. The gyro sensor  180 B may be further used in a navigation scenario and a somatic game scenario. 
     The barometric pressure sensor  180 C is configured to measure barometric pressure. In some embodiments, the electronic device  100  calculates an altitude based on a barometric pressure value measured by the barometric pressure sensor  180 C, to assist in positioning and navigation. 
     The magnetic sensor  180 D includes a Hall sensor. The electronic device  100  may detect opening and closing of a flip cover by using the magnetic sensor  180 D. In some embodiments, when the electronic device  100  is a clamshell phone, the electronic device  100  may detect opening and closing of a flip cover by using the magnetic sensor  180 D, to set a feature such as automatic unlocking through flipping based on a detected opening or closing state of the flip cover. 
     The acceleration sensor  180 E may detect accelerations in various directions (usually on three axes) of the electronic device  100 , and may detect magnitude and a direction of gravity when the electronic device  100  is still. The acceleration sensor  180 E may be further configured to identify a posture of the electronic device, and is applied to applications such as a pedometer and switching between a landscape mode and a portrait mode. 
     The distance sensor  180 F is configured to measure a distance. The electronic device  100  may measure the distance in an infrared or a laser manner. In some embodiments, in a shooting scenario, the electronic device  100  may measure a distance by using the distance sensor  180 F to implement quick focusing. 
     The optical proximity sensor  180 G may include, for example, a light-emitting diode (LED) and an optical detector such as a photodiode. The light-emitting diode may be an infrared light-emitting diode. The electronic device  100  emits infrared light by using the light emitting diode. The electronic device  100  detects infrared reflected light from a nearby object by using the photodiode. When detecting sufficient reflected light, the electronic device  100  may determine that there is an object near the electronic device  100 . When detecting insufficient reflected light, the electronic device  100  may determine that there is no object near the electronic device  100 . The electronic device  100  may detect, by using the optical proximity sensor  180 G, that the user holds the electronic device  100  close to an ear to make a call, to automatically perform screen-off for power saving. The optical proximity sensor  180 G may also be used in a smart cover mode or a pocket mode to automatically perform screen unlocking or locking. 
     The ambient light sensor  180 L is configured to sense ambient light luminance. The electronic device  100  may adaptively adjust brightness of the display  194  based on the sensed ambient light brightness. The ambient light sensor  180 L may be further configured to automatically adjust a white balance during shooting. The ambient light sensor  180 L may also cooperate with the optical proximity sensor  180 G to detect whether the electronic device  100  is in a pocket, to avoid an accidental touch. 
     The fingerprint sensor  180 H is configured to collect a fingerprint. The electronic device  100  may use a feature of the collected fingerprint to implement fingerprint-based unlocking, application lock access, fingerprint-based shooting, fingerprint-based call answering, and the like. 
     The temperature sensor  180 J is configured to detect a temperature. In some embodiments, the electronic device  100  executes a temperature processing policy based on the temperature detected by the temperature sensor  180 J. For example, when the temperature reported by the temperature sensor  180 J exceeds a threshold, the electronic device  100  degrades performance of a processor near the temperature sensor  180 J, to reduce power consumption for thermal protection. In some other embodiments, when the temperature is lower than another threshold, the electronic device  100  heats up the battery  142 , to avoid abnormal shutdown of the electronic device  100  caused by a low temperature. In some other embodiments, when the temperature is lower than still another threshold, the electronic device  100  boosts an output voltage of the battery  142  to avoid abnormal shutdown caused by a low temperature. 
     The touch sensor  180 K is also referred to as a “touch panel”. The touch sensor  180 K may be disposed on the display  194 , and the touch sensor  180 K and the display  194  form a touchscreen, which is also referred to as a “touchscreen”. The touch sensor  180 K is configured to detect a touch operation acting on or near the touch sensor  180 K. The touch sensor may transfer the detected touch operation to the application processor, to determine a type of a touch event. The display  194  may provide a visual output related to the touch operation. In some other embodiments, the touch sensor  180 K may also be disposed on a surface of the electronic device  100  in a position different from that of the display  194 . 
     The bone conduction sensor  180 M may obtain a vibration signal. In some embodiments, the bone conduction sensor  180 M may obtain a vibration signal of a vibration bone of a human voice part. The bone conduction sensor  180 M may also be in contact with a human pulse, and receive a blood pressure beating signal. In some embodiments, the bone conduction sensor  180 M may alternatively be disposed in a headset, to obtain a bone conduction headset. The audio module  170  may obtain a voice signal through parsing based on the vibration signal that is of the vibration bone of the vocal part and that is obtained by the bone conduction sensor  180 M, to implement a voice function. The application processor may parse heart rate information based on the blood pressure beating signal obtained by the bone conduction sensor  180 M, to implement a heart rate detection function. 
     The button  190  includes a power button, a volume button, and the like. The button  190  may be a mechanical button, or may be a touch button. The electronic device  100  may receive a button input, and generate a button signal input related to a user setting and function control of the electronic device  100 . 
     The motor  191  may generate a vibration prompt. The motor  191  may be configured to provide an incoming call vibration prompt or a touch vibration feedback. For example, touch operations performed on different applications (for example, shooting and audio playing) may correspond to different vibration feedback effects. The motor  191  may also correspond to different vibration feedback effects for touch operations performed on different areas of the display  194 . Different application scenarios (for example, a time reminder scenario, an information receiving scenario, an alarm clock scenario, and a game scenario) may also correspond to different vibration feedback effects. A touch vibration feedback effect may alternatively be customized. 
     The indicator  192  may be an indicator light, and may be configured to indicate a charging status and a power change, or may be configured to indicate a message, a missed call, a notification, and the like. 
     The SIM card interface  195  is configured to connect to a SIM card. The SIM card may be inserted into the SIM card interface  195  or detached from the SIM card interface  195 , to implement contact with or separation from the electronic device  100 . The electronic device  100  may support one or N SIM card interfaces, where N is a positive integer greater than 1. The SIM card interface  195  may support a nano-SIM card, a micro-SIM card, a SIM card, and the like. A plurality of cards may be simultaneously inserted in a same SIM card interface  195 . The plurality of cards may be of a same type, or may be of different types. The SIM card interface  195  may be further compatible with different types of SIM cards. The SIM card interface  195  may also be compatible with the external storage card. The electronic device  100  interacts with a network by using the SIM card, to implement functions such as calling and data communication. In some embodiments, the electronic device  100  uses an eSIM, namely, an embedded SIM card. The eSIM card may be embedded into the electronic device  100 , and cannot be separated from the electronic device  100 . 
     A software system of the electronic device  100  may use a layered architecture, an event-driven architecture, a microkernel architecture, a micro service architecture, or a cloud architecture. In the embodiments of the present invention, an Android system of a layered architecture is used as an example to describe a software structure of the electronic device  100 . 
       FIG. 2  is a block diagram of the software structure of the electronic device  100  according to an embodiment of the present invention. 
     In the layered architecture, software is divided into several layers, and each layer has a clear role and task. The layers communicate with each other through a software interface. In some embodiments, the Android system is divided into four layers: an application layer, an application framework layer, an Android runtime and system library, and a kernel layer from top to bottom. 
     The application layer may include a series of application packages. 
     As shown in  FIG. 2 , the application packages may include applications such as Camera, Gallery, Calendar, Phone, Map, Navigation, WLAN, Bluetooth, Music, Video, and Messages. 
     The application framework layer provides an application programming interface (API) and a programming framework for an application at the application layer. The application framework layer includes some predefined functions. 
     As shown in  FIG. 2 , the application framework layer may include a window manager, a content provider, a view system, a phone manager, a resource manager, a notification manager, and the like. 
     The window manager is configured to manage a window program. The window manager may obtain a size of the display, determine whether there is a status bar, perform screen locking, take a screenshot, and the like. 
     The content provider is configured to store and obtain data, and enable the data to be accessed by an application. The data may include a video, an image, audio, calls that are made and received, a browsing history and a bookmark, a phone book, and the like. 
     The view system includes visual controls such as a control for displaying text and a control for displaying a picture. The view system may be configured to construct an application. A display interface may include one or more views. For example, a display interface including a Messages notification icon may include a text display view and a picture display view. 
     The phone manager is configured to provide a communications function of the electronic device  100 , for example, management of a call status (including answering, declining, or the like). 
     The resource manager provides various resources for an application, such as a localized character string, an icon, an image, a layout file, and a video file. 
     The notification manager enables an application to display notification information in a status bar, and may be configured to convey a notification message. The notification manager may automatically disappear after a short pause without requiring a user interaction. For example, the notification manager is configured to notify download completion, give a message notification, and the like. The notification manager may alternatively be a notification that appears in a top status bar of the system in a form of a graph or a scroll bar text, for example, a notification of an application program running on a background or a notification that appears on the interface in a form of a dialog window. For example, text information is prompted in the status bar, a prompt tone is produced, the electronic device vibrates, or an indicator blinks. 
     The Android runtime includes a kernel library and a virtual machine. The Android runtime is responsible for scheduling and management of the Android system. 
     The kernel library includes two parts: a function that needs to be invoked in java language and a kernel library of Android. 
     The application layer and the application framework layer run on the virtual machine. The virtual machine executes java files of the application layer and the application framework layer as binary files. The virtual machine is configured to perform functions such as object lifecycle management, stack management, thread management, security and exception management, and garbage collection. 
     The system library may include a plurality of functional modules, for example, a surface manager (surface manager), a media library, a three-dimensional graphics processing library (for example, OpenGL ES), and a 2D graphics engine (for example, SGL). 
     The surface manager is configured to manage a display subsystem and provide fusion of 2D and 3D layers for a plurality of applications. 
     The media library supports playing and recording of a plurality of commonly used audio and video formats, static image files, and the like. The media library may support a plurality of audio and video coding formats such as MPEG-4, H.264, MP3, AAC, AMR, JPG, and PNG. 
     The three-dimensional graphics processing library is configured to implement three-dimensional graphics drawing, image rendering, composition, layer processing, and the like. 
     The 2D graphics engine is a drawing engine for 2D drawing. 
     The kernel layer is a layer between hardware and software. The kernel layer includes at least a display driver, a camera driver, an audio driver, and a sensor driver. 
     The following describes an example of a working process of software and hardware of the electronic device  100  with reference to a photographing scenario. 
     When the touch sensor  180 K receives a touch operation, a corresponding hardware interrupt is sent to the kernel layer. The kernel layer processes the touch operation into an original input event (including information such as touch coordinates and a time stamp of the touch operation). The original input event is stored at the kernel layer. The application program framework layer obtains the original input event from the kernel layer, and identifies a control corresponding to the input event. An example in which the touch operation is a touch tap operation, and a control corresponding to the tap operation is a control of a camera application icon is used. The camera application invokes an interface at the application framework layer to enable the camera application, then enables a camera driver by invoking the kernel layer, and captures a static image or a video by using the camera  193 . 
     The embodiments of this application provide a screen projection method. The method may be applied to mobile office and another application scenario in which display data on a terminal needs to be displayed on a plurality of displays. For example, as shown in  FIG. 3 , an electronic device  100  may be a mobile phone, a tablet computer, a wearable device, an augmented reality (AR)/virtual reality (VR) device, a notebook computer, an ultra-mobile personal computer (UMPC), a netbook, a personal digital assistant (PDA), or the like. This is not limited in the embodiments of this application. An external display device  200  in the embodiments of this application may be any display apparatus such as a display of a PC, a television, a tablet computer, or a projector. 
     As shown in  FIG. 3 , the electronic device  100  may establish a wireless connection to the external display device  200  in wireless communication manner (for example, Wi-Fi or Bluetooth). Alternatively, the electronic device  100  may establish a connection to the external display device  200  in a wired manner (for example, a data cable). 
     In the embodiments of this application, the electronic device  100  may be further connected to the external display device  200  through a transit device. The transit device may be plugged into a universal serial bus (USB) interface of a data cable, and a Type-C interface of the data cable is plugged into the electronic device  100 . The transit device may be further connected to the external display device  200  through an adapter cable. The adapter cable may include any one of a high definition multimedia interface (HDMI) adapter cable, a video graphics array (VGA) adapter cable, a digital visual interface (DVI) adapter cable, and the like. 
     The transit device in the embodiments of this application may be a mobile high-definition link (MHL) device. The MHL device may simultaneously transmit an audio signal and a video signal in the electronic device  100  (for example, a mobile phone) to the external display device  200  for displaying. 
     The electronic device  100  may be used as a master device, and the external display device  200  may be used as a slave device of the electronic device  100 . After the electronic device  100  establishes a connection to the external display device  200 , the electronic device  100  has two displays. One is a touchscreen  300  of the electronic device  100 , and the other is a display of the external display device  200  connected to the electronic device  100 . 
     Currently, the electronic device  100  may enable a multi-application split-screen function, and display interfaces of a plurality of applications in different areas on the touchscreen  300 . When the electronic device  100  enables a screen projection mode and establishes a connection to the external display device  200 , the electronic device  100  may send display content displayed on the touchscreen  300  and to-be-output audio content to the external display device  200 . After receiving the display content and the audio content, the external display device  200  may display the received display content on the display of the external display device  200 , and play the audio content by using an audio output apparatus of the external display device. The display content on the display of the external display device  200  is consistent with the display content on the touchscreen  300  of the electronic device  100 . For example, the electronic device  100  may display an application interface of Video, an application interface of Settings, an application interface of Music, an application interface of Gallery, and an application interface of Messages in different areas on the touchscreen  300 . When the electronic device  100  projects, onto the external display device  200 , the display content on the touchscreen  300 , the external display device  200  also displays an application interface of Video, an application interface of Settings, an application interface of Music, an application interface of Gallery, and an application interface of Messages in different areas on the display. 
     A plurality of application interfaces (for example, the application interface of Video, the application interface of Settings, the application interface of Music, the application interface of Gallery, and the application interface of Messages) are displayed in different areas on the touchscreen  300  of the electronic device  100 , and some application interfaces (for example, the application interface of Gallery and the application interface of Messages) may involve user privacy. If these application interfaces involving user privacy are projected onto the external display device  200 , these application interfaces are easy to be seen by another person. This cases leakage of user privacy, and brings bad experience to the user. 
     Therefore, the embodiments of this application provide a screen projection method. When the plurality of application interfaces are split-screen displayed on the touchscreen  300  of the electronic device  100 , and when the electronic device  100  enables the screen projection function and establishes a connection to the external display device  300 , the electronic device  100  may receive a selection operation of a user. The selection operation of the user is selection on the plurality of application interfaces split-screen displayed on the touchscreen  300 . In response to the selection operation, the electronic device  100  may project one or more application interfaces selected by the user onto the display of the external display device  200  for displaying. In this way, the electronic device  100  can project, based on the selection operation of the user onto the display of the external display device  200  for displaying, the one or more application interfaces selected by the user on the touchscreen  300 . This ensures that an application interface involving user privacy is projected only after the user agrees and confirms, to ensure user privacy and improve user experience. 
     The following describes the screen projection method provided in the embodiments of this application in detail with reference to the accompanying drawings. 
     In some application scenarios, a user needs to simultaneously process a plurality of application tasks on the electronic device  100 . To meet such a requirement of the user, the electronic device  100  may display a plurality of application interfaces (for example, an application interface of Video, an application interface of Settings, an application interface of Music, an application interface of Gallery, and an application interface of Messages) in different areas on the touchscreen  300 . When the plurality of application interfaces are displayed in different areas on the touchscreen  300  of the electronic device  100 , and when the electronic device  100  receives an input operation of the user and enables a screen projection function, the electronic device  100  may establish a connection (for example, a Wi-Fi connection or a wired connection) to the external display device  200 , and display a projection add control in a display area of each application interface on the touchscreen  300 . The electronic device  100  may receive an input operation on the projection add control. In response to the input operation, the electronic device may project the application interface corresponding to the projection add control onto the external display device  200 . After the application interface on the touchscreen  300  is projected onto the display of the external display device  200 , a projection cancel control is displayed in the display area of the application interface. The electronic device  100  may receive an input operation on the projection cancel control. In response to the input operation on the projection cancel control, the electronic device  100  may cancel projection of the application interface onto the display of the external display device  200 . In this way, the electronic device  100  can select, based on the input operation of the user, the one or more application interfaces from the plurality of application interfaces split-screen displayed on the touchscreen  300 , and project the one or more application interfaces onto the display of the external display device  200 , to ensure that an application interface involving user privacy is projected only after the user agrees and confirms. This ensures user privacy. 
     For example, as shown in  FIG. 4A-1  and  FIG. 4A-2 , the electronic device  100  displays an application interface  410  of Video, an application interface  420  of Settings, an application interface  430  of Music, an application interface  440  of Gallery, and an application interface  450  of Messages in different areas on the touchscreen  300 . The application interface  410  of Video includes a video play screen, a play/pause button, a play progress bar, and the like. The application interface  420  of Settings includes a setting item search box, an account login option, one or more setting options, and the like (for example, a wireless and network settings option, a device connectivity settings option, applications and notifications settings option, a battery settings option, a display settings option, and a sound settings option). The application interface  430  of Music includes a song name and a singer, a volume adjustment button, a song download button, a song share button, a more function button, a play progress bar, a play mode switching button, a previous song button, a play/pause button, a next song button, a playlist button, and the like. The application interface  440  of Gallery includes a photo control, an album control, a discover control, and the like. When the user taps the album control, the electronic device  100  displays, in the application interface  440  of Gallery, a page corresponding to the album control. The page corresponding to the album control includes one or more album options (for example, an all-photos option, an all videos option, a camera option, a screenshots option, a recently deleted option, a favorite option). The application interface  450  of Messages includes a name and contact information of a contact, and a message chat window, and further includes a picture or video add button, a text enter box, an emoji enter button, a message sending button, and the like below the message chat window. The message chat window includes chat information between the user and the contact (for example, “uncle”). 
     The electronic device  100  may receive an input operation of the user, enable the screen projection function, and establish a connection (for example, a wireless connection such as Wi-Fi or a wired connection via an HDMI data cable) between the electronic device  100  and the external display device  200 . The following provides descriptions by using an example in which the electronic device  100  establishes a wireless connection to the external display device  200 , to perform wireless projection. 
     For example, as shown in  FIG. 4B-1  and  FIG. 4B-2 , the electronic device  100  may receive an input operation  426  (for example, swiping down from the top of the touchscreen  300 ) on the top of the touchscreen  300 . In response to the input operation  426 , the electronic device  100  may display a window  460  shown in  FIG. 4C-1  and  FIG. 4C-2 . 
     As shown in  FIG. 4C-1  and  FIG. 4C-2 , some function controls (for example, a WLAN on/off control, a Bluetooth on/off control, a flashlight on/off control, a ringing type switch control, an auto-rotate on/off control, a Huawei share (Huawei share) on/off control, an airplane mode on/off control, a mobile data on/off control, a location on/off control, a screenshot on/off control, an eye comfort mode on/off control, a hotspot on/off control, a screen recorder on/off control, a large-screen projection on/off control  461 , and an NFC on/off control) may be displayed in the window  460 . The electronic device  100  may receive an input operation  462  (for example, tapping) by the user on the large-screen projection on/off control  461 . In response to the input operation  462 , the electronic device  100  may display a wireless projection selection window  470  shown in  FIG. 4D-1  and  FIG. 4D-2  on the touchscreen  300 . 
     As shown in  FIG. 4D-1  and  FIG. 4D-2 , the wireless projection selection window  470  may display a projection device option  471 , a help view button, and a cancel button. A name (for example, “AC200”) of a projection device is displayed in the projection device option  471 , and the electronic device  100  may find a name (for example, AC200) of the projection device by using a wireless technology such as Wi-Fi. The name “AC200” may be used to refer to the external display device  200 . The electronic device  100  may receive an input operation  472  (for example, tapping) by the user on the projection device option  471 . In response to the input operation  472 , the electronic device  100  may establish a connection to the external display device  200  by using a wireless technology such as Wi-Fi, and display a projection add button in each application interface displayed on the touchscreen  300 , as shown in  FIG. 4E-1  and  FIG. 4E-2 . 
     As shown in  FIG. 4E-1  and  FIG. 4E-2 , the electronic device  100  may display a projection add button  411  in an upper right corner of the application interface  410  of Video on the touchscreen  300 , the electronic device  100  may display a projection add button  421  in an upper right corner of the application interface  420  of Settings on the touchscreen  300 , the electronic device  100  may display a projection add button  431  in an upper right corner of the application interface  430  of Music on the touchscreen  300 , the electronic device  100  may display a projection add button  441  in an upper right corner of the application interface  440  of Gallery on the touchscreen  300 , and the electronic device  100  may display a projection add button  451  in an upper right corner of the application interface  450  of Messages on the touchscreen  300 . The projection add buttons (for example, the projection add button  411 , the projection add button  421 , the projection add button  431 , the projection add button  441 , and the projection add button  451 ) each are not limited to being displayed in the upper right corner of the application interface, or may be displayed in another position in the application interface. This is not limited herein. 
     After a projection add button is triggered by the user, the electronic device may project an application interface corresponding to the projection add button onto the external display device  200  for displaying. An interface element in the application interface corresponding to the projection add button is the same as an interface element in an application interface displayed on the external display device  200 , and the two application interfaces may be considered as a same application interface. When a same application interface is displayed on different devices, a display ratio is adaptively adjusted. For example, because the touchscreen of the electronic device and the display of the external display device are different in size, a display ratio of an application interface of Video on the touchscreen of the electronic device is different from a display ratio of the same application interface of Video on the display of the external display device. 
     The projection add button  411  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection add button  411 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  410  of Video displayed on the touchscreen  300 . The projection add button  421  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection add button  421 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  420  of Settings displayed on the touchscreen  300 . The projection add button  431  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection add button  431 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  430  of Music displayed on the touchscreen  300 . The projection add button  441  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection add button  441 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  440  of Gallery displayed on the touchscreen  300 . The projection add button  451  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection add button  451 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  450  of Messages displayed on the touchscreen  300 . 
     For example, as shown in  FIG. 4E-1  and  FIG. 4E-2 , the electronic device  100  may receive an input operation  412  (for example, tapping) by the user on the projection add button  411  on the touchscreen  300 . In response to the input operation  412 , as shown in  FIG. 4F-1  and  FIG. 4F-2 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  410  of Video displayed on the touchscreen  300 . 
     As shown in  FIG. 4F-1  and  FIG. 4F-2 , an application interface  510  of Video is displayed on the display of the external display device  200 . Display content in the application interface  510  of Video displayed on the display of the external display device  200  is the same as display content in the application interface  410  of Video displayed on the touchscreen  300  of the electronic device  100 . 
     In a possible implementation, a layout of the plurality of application interfaces on the touchscreen  300  of the electronic device  100  is the same as a layout of a plurality of application interfaces on the display of the external display device  200 . 
     After the user selects one or more application interfaces on the electronic device  100  to be projected onto the external display device  200  and the electronic device  100  has performed projection display, the user may further continue to trigger a projection add button in an interface that is not projected and that is on the electronic device  100 , and the application interface is additionally projected onto the external display device  200 . 
     For example, as shown in  FIG. 4F-1  and  FIG. 4F-2 , the application interface  410  of Video is displayed in a left display area of the touchscreen  300 , and similarly, the application interface  510  of Video is displayed in a left display area of the display of the external display device  200 . After projecting, onto the display of the external display device  200 , the application interface  410  of Video displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  422  (for example, tapping) by the user on the projection add button  421  in the application interface  420  of Settings. In response to the input operation  422 , as shown in  FIG. 4G-1  and  FIG. 4G-2 , the electronic device  100  may further project the application interface  420  of Settings onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 4G-1  and  FIG. 4G-2 , the application interface  510  of Video and an application interface  520  of Settings are displayed on the display of the external display device  200 . Display content in the application interface  520  of Settings is the same as display content in the application interface  420  of Settings displayed on the touchscreen  300  of the electronic device  100 . Relative positions of the application interface  510  of Video and the application interface  520  of Settings that are displayed on the display of the external display device  200  are the same as relative positions of the application interface  410  of Video and the application interface  420  of Settings that are displayed on the touchscreen  300 . The application interface  420  of Settings is displayed in an upper middle display area of the touchscreen  200 . Similarly, the application interface  520  of Settings is displayed in an upper middle display area of the display of the external display device  200 . 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video and the application interface  420  of Settings that are displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  432  (for example, tapping) by the user on the projection add button  431  in the application interface  430  of Music. In response to the input operation  432 , as shown in  FIG. 4H-1  and  FIG. 4H-2 , the electronic device  100  may further project the application interface  430  of Music onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video and the application interface  420  of Settings onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 4H-1  and  FIG. 4H-2 , the application interface  510  of Video, the application interface  520  of Settings, and an application interface  530  of Music are displayed on the display of the external display device  200 . Display content in the application interface  530  of Music is the same as display content in the application interface  430  of Music displayed on the touchscreen  300  of the electronic device  100 . Relative positions of the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music that are displayed on the display of the external display device  200  are the same as relative positions of the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music that are displayed on the touchscreen  300 . The application interface  430  of Music is displayed in a lower middle display area of the touchscreen  200 . Similarly, the application interface  530  of Music is displayed in a lower middle display area of the display of the external display device  200 . 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music that are displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  442  (for example, tapping) by the user on the projection add button  441  in the application interface  440  of Gallery. In response to the input operation  442 , as shown in  FIG. 4I-1  and  FIG. 4I-2 , the electronic device  100  may further project the application interface  440  of Gallery onto the display of the external display device  300  for displaying while projecting the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 4I-1  and  FIG. 4I-2 , the application interface  510  of Video, the application interface  520  of Settings, the application interface  530  of Music, and an application interface  540  of Gallery are displayed on the display of the external display device  200 . Display content in the application interface  540  of Gallery is the same as display content in the application interface  440  of Gallery displayed on the touchscreen  300  of the electronic device  100 . Relative positions of the application interface  510  of Video, the application interface  520  of Settings, the application interface  540  of Music, and the application interface  540  of Gallery that are displayed on the display of the external display device  200  are the same as relative positions of the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery that are displayed on the touchscreen  300 . The application interface  440  of Gallery is displayed in an upper right display area of the touchscreen  200 . Similarly, the application interface  540  of Gallery is displayed in an upper right display area of the display of the external display device  200 . 
     In a possible implementation, when the electronic device  100  projects an application interface displayed on the touchscreen  300  to the display of the external display device  200 , the electronic device  100  may switch a projection add button displayed in the application interface on the touchscreen  300  to a projection cancel button. The projection cancel button may be used to receive an input operation (for example, tapping) by the user. In response to the input operation on the projection cancel button, the electronic device  100  may cancel projection of the application interface corresponding to the projection cancel button onto the display of the external display device  200  for displaying. 
     For example, as shown in  FIG. 4F-1  and  FIG. 4F-2 , after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the application interface  410  of Video on the touchscreen  300 , the electronic device  100  may replace the projection add button  411  displayed in the application interface  410  of Video with a projection cancel button  413 . As shown in  FIG. 4G-1  and  FIG. 4G-2 , after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the application interface  420  of Settings on the touchscreen  300 , the electronic device  100  may replace the projection add button  421  displayed in the application interface  420  of Settings with a projection cancel button  423 . As shown in  FIG. 4H-1  and  FIG. 4H-2 , after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the application interface  430  of Music on the touchscreen  300 , the electronic device  100  may replace the projection add button  431  displayed in the application interface  430  of Music with a projection cancel button  433 . As shown in  FIG. 4I-1  and  FIG. 4I-2 , after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the application interface  440  of Gallery on the touchscreen  300 , the electronic device  100  may replace the projection add button  441  displayed in the application interface  440  of Gallery with a projection cancel button  443 . 
     The projection cancel button  413  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation (for example, tapping) on the projection cancel button  413 , the electronic device  100  may cancel projection, onto the display of the external display device  200 , of the application interface  410  of Video displayed on the touchscreen  300 . Similarly, the user triggers the projection cancel button  423 ,  433 , or  443 , so that the electronic device  100  cancels projection of the application interface  420  of Settings, the application interface  430  of Music, or the application interface  440  of Gallery onto the external display device  200  for displaying. 
     For example, as shown in  FIG. 4I-1  and  FIG. 4I-2 , the electronic device  100  may receive an input operation  444  (for example, tapping) by the user on the projection cancel button  443  displayed in the application interface  440  of Gallery. In response to the input operation  444 , as shown in  FIG. 4J-1  and  FIG. 4J-2 , the electronic device  100  may cancel projection of the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 4J-1  and  FIG. 4J-2 , the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music are displayed on the display of the external display device  200 . The display content in the application interface  530  of Music is the same as the display content in the application interface  430  of Music displayed on the touchscreen  300  of the electronic device  100 . The relative positions of the application interface  510  of Video, the application interface  520  of Settings, and the application interface  540  of Music that are displayed on the display of the external display device  200  are the same as the relative positions of the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music that are displayed on the touchscreen  300 . After the electronic device  100  cancels projection of the application interface  440  of Gallery onto the display of the external display device  200  for displaying, the electronic device  100  may replace the projection cancel button  443  displayed in the application interface  440  of Gallery with the projection add button  441 . 
     In a possible implementation, after establishing the connection to the external display device  200 , the electronic device  100  may determine whether the external display device  200  has an audio output apparatus. If the external display device  200  has an audio output apparatus, the electronic device  100  may send to-be-played audio data to the external display device  200 , and the audio output apparatus of the external display device  200  plays the to-be-played audio data. If the external display device  200  has no audio output apparatus, the electronic device  100  may play the audio data by using an audio output apparatus on the electronic device  100 . 
     For example, as shown in  FIG. 4E-1  and  FIG. 4E-2 , the external display device  200  has an audio output apparatus. After the electronic device  100  establishes the connection to the external display device  200 , the electronic device  100  may receive the input operation  412  (for example, tapping) by the user on the projection add button  411  on the touchscreen  300 . In response to the input operation  412 , the electronic device  100  may project the application interface  410  of Video onto the display of the external display device  200  for displaying, and send, to the external display device  200 , audio data that is being played by Video. The external display device  200  may display the application interface  510  of Video on the display, and play the audio data by using the audio output apparatus. 
     In a possible implementation, when the electronic device  100  projects, onto the display of the external display device  200  for displaying, the one or more application interfaces displayed on the touchscreen  300 , a layout of the one or more application interfaces displayed on the display of the external display device  200  is different from a layout of the one or more application interfaces displayed on the touchscreen  300 . In other words, before projecting, onto the external display device  200 , the one or more application interfaces displayed on the touchscreen  300 , the electronic device  100  may change relative positions of the one or more application interfaces displayed on the display of the external display device  200 , splice, into one image, the one or more application interfaces obtained after the layout is changed, and send the image to the external display device  200 . The external display device  200  displays, on the display, the one or more application interfaces obtained after the layout is changed. In another possible implementation, the electronic device  100  sends, to the external display device  200 , image data of the one or more application interfaces displayed on the touchscreen  300 . After receiving the image data of the one or more application interfaces, the external display device  200  may allocate a display area to each application interface on the display, and may display the one or more application interfaces in respective display areas. In this way, when the electronic device  100  projects some application interfaces on the touchscreen  300  onto the external display device  200 , the external display device  200  may display some application interfaces by using all display areas of the display, to fully utilize the display areas of the display of the external display device  200 . 
     For example, as shown in  FIG. 5A-1  and  FIG. 5A-2 , the electronic device  100  may receive an input operation  412  (for example, tapping) by the user on the projection add button  411  on the touchscreen  300 . In response to the input operation  412 , as shown in  FIG. 5B-1  and  FIG. 5B-2 , the electronic device  100  may project, onto the display of the external display device  200 , the application interface  410  of Video displayed on the touchscreen  300 . Because only one application interface (for example, the application interface  410  of Video) is selected for projection, the external display device  100  may display an application interface  551  of Video in full screen on the display. Display content in the application interface  551  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300 , but a proportion of the application interface  551  of Video is different from a proportion of the application interface  410  of Video. 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  422  (for example, tapping) by the user on the projection add button  421  on the touchscreen  300 . In response to the input operation  422 , as shown in  FIG. 5C-1  and  FIG. 5C-2 , the electronic device  100  may further project the application interface  420  of Settings onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 5C-1  and  FIG. 5C-2 , because the user selects two application interfaces (for example, the application interface  410  of Video and the application interface  420  of Settings) for projection, the external display device  100  may divide a display area of the display into two display areas (for example, a left display area and a right display area), may display an application interface  561  of Video in the left display area, and may display an application interface  562  of Settings in the right display area. Display content in the application interface  561  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300 , but a proportion of the application interface  561  of Video is different from a proportion of the application interface  410  of Video. Display content in the application interface  562  of Settings is the same as the display content in the application interface  420  of Settings displayed on the touchscreen  300 , but a proportion of the application interface  562  of Settings is different from a proportion of the application interface  420  of Settings. 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video and the application interface  420  of Settings that are displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  432  (for example, tapping) by the user on the projection add button  431  on the touchscreen  300 . In response to the input operation  432 , as shown in  FIG. 5D-1  and  FIG. 5D-2 , the electronic device  100  may further project the application interface  430  of Music onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video and the application interface  420  of Settings onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 5D-1  and  FIG. 5D-2 , because the user selects three application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music) for projection, the external display device  100  may divide the display area of the display into three display areas (for example, a left display area, an upper right display area, and a lower right display area), may display an application interface  571  of Video in the left display area, may display an application interface  572  of Settings in the upper right display area, and may display an application interface  573  of Music in the lower right display area. Display content in the application interface  571  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300 , but a proportion of the application interface  571  of Video is different from a proportion of the application interface  410  of Video. Display content in the application interface  572  of Settings is the same as the display content in the application interface  420  of Settings displayed on the touchscreen  300 , but a proportion of the application interface  572  of Settings is different from a proportion of the application interface  430  of Settings. Display content in the application interface  573  of Music is the same as the display content in the application interface  430  of Music displayed on the touchscreen  300 , but a proportion of the application interface  573  of Music is different from a proportion of the application interface  430  of Music. 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music that are displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  442  (for example, tapping) by the user on the projection add button  441  on the touchscreen  300 . In response to the input operation  442 , as shown in  FIG. 5E-1  and  FIG. 5E-2 , the electronic device  100  may further project the application interface  440  of Gallery onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 5E-1  and  FIG. 5E-2 , because the user selects four application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery) for projection, the external display device  100  may divide the display area of the display into four display areas (for example, an upper left display area, a lower left display area, an upper right display area, and a lower right display area), may display an application interface  581  of Video in the upper left display area, may display an application interface  582  of Settings in the upper right display area, may display an application interface  583  of Music in the lower right display area, and may display an application interface  584  of Gallery in the lower left display area. Display content in the application interface  581  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300 , but a proportion of the application interface  581  of Video is different from a proportion of the application interface  410  of Video. Display content in the application interface  582  of Settings is the same as the display content in the application interface  420  of Settings displayed on the touchscreen  300 , but a proportion of the application interface  582  of Settings is different from a proportion of the application interface  430  of Settings. Display content in the application interface  583  of Music is the same as the display content in the application interface  430  of Music displayed on the touchscreen  300 , but a proportion of the application interface  583  of Music is different from a proportion of the application interface  430  of Music. Display content in the application interface  584  of Gallery is the same as the display content in the application interface  440  of Gallery displayed on the touchscreen  300 , but a proportion of the application interface  584  of Gallery is different from a proportion of the application interface  440  of Gallery. 
     After projecting, onto the display of the external display device  200 , the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery that are displayed on the touchscreen  300 , the electronic device  100  may further receive an input operation  452  (for example, tapping) by the user on the projection add button  451  on the touchscreen  300 . In response to the input operation  452 , as shown in  FIG. 5F-1  and  FIG. 5F-2 , the electronic device  100  may further project the application interface  450  of Messages onto the display of the external display device  200  for displaying while projecting the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 5F-1  and  FIG. 5F-2 , because the user selects all the application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, the application interface  440  of Gallery, and the application interface  450  of Messages) on the touchscreen  300  of the electronic device  100  for projection, the external display device  100  may divide the display area of the display into five display areas (for example, a left display area, an upper middle display area, a lower middle display area, an upper right display area, and a lower right display area). The electronic device  100  may display an application interface  591  of Video in the left display area, may display an application interface  592  of Settings in the upper middle display area, may display an application interface  593  of Music in the lower middle display area, may display an application interface  594  of Gallery in an upper left display area, and may display an application interface  595  of Messages in a lower left display area. Display content in the application interface  591  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300 , but a proportion of the application interface  591  of Video is different from a proportion of the application interface  410  of Video. Display content in the application interface  592  of Settings is the same as the display content in the application interface  420  of Settings displayed on the touchscreen  300 , but a proportion of the application interface  592  of Settings is different from a proportion of the application interface  430  of Settings. Display content in the application interface  593  of Music is the same as the display content in the application interface  430  of Music displayed on the touchscreen  300 , but a proportion of the application interface  593  of Music is different from a proportion of the application interface  430  of Music. Display content in the application interface  594  of Gallery is the same as the display content in the application interface  440  of Gallery displayed on the touchscreen  300 , but a proportion of the application interface  594  of Gallery is different from a proportion of the application interface  440  of Gallery. Display content in the application interface  595  of Gallery is the same as the display content in the application interface  450  of Messages displayed on the touchscreen  300 , but a proportion of the application interface  595  of Gallery is different from a proportion of the application interface  450  of Messages. 
     In some application scenarios, a user needs to simultaneously process a plurality of application tasks on the electronic device  100 . To meet such requirement of the user, the electronic device  100  may display a plurality of application interfaces (for example, an application interface of Video, an application interface of Settings, an application interface of Music, an application interface of Gallery, and an application interface of Messages) in different areas on the touchscreen  300 . When the plurality of application interfaces are displayed in different areas on the touchscreen  300  of the electronic device  100 , when the electronic device  100  receives an input operation of the user and enables a screen projection function, the electronic device  100  may establish a connection (for example, a wireless connection such as Wi-Fi or a wired connection) to the external display device  200 , and display an application selection window on the touchscreen  300 . The application selection window includes a plurality of application options, and the plurality of application options may be options of an icon type (for example, an application icon of Video, an application icon of Settings, an application icon of Music, an application icon of Gallery, an application icon of Messages) or may be options of a text type. This is not limited herein. Each of the plurality of application interfaces displayed in different areas on the touchscreen  300  corresponds to an application option in the application selection window. The electronic device  100  may receive a selection operation that is performed by the user on the plurality of application options in the application selection window. In response to the selection operation, the electronic device  100  may project, onto the display of the external display device  200 , one or more application interfaces corresponding to one or more application options selected by the user. In this way, the electronic device  100  can select, based on the input operation of the user, the one or more application interfaces from the plurality of application interfaces split-screen displayed on the touchscreen  300 , and project the one or more application interfaces onto the display of the external display device  200 , to ensure that an application interface involving user privacy is projected only after the user agrees and confirms. This ensures user privacy. 
     For example, the electronic device  100  receives the input operation (for example, the input operation  472  on the projection device option  471  in  FIG. 4D-1  and  FIG. 4D-2 ) by the user. In response to the input operation of the user, the electronic device  100  establishes a connection to the external display device  200 , and displays an application selection window  610  shown in  FIG. 6A-1  and  FIG. 6A-2  on the touchscreen  300 . 
     As shown in  FIG. 6A-1  and  FIG. 6A-2 , the application selection window  610  includes a plurality of application options, an OK button  616 , a cancel button  617 , and a window close button  618 . For example, the application selection window  610  includes an application option  611  of Video, an application option  612  of Settings, an application option  613  of Music, an application option  614  of Gallery, and an application option  615  of Messages. The application option  611  of Video corresponds to an application interface  410  of Video displayed on the touchscreen  300 , the application option  612  of Settings corresponds to an application interface  420  of Settings displayed on the touchscreen  300 , the application option  613  of Music corresponds to an application interface  430  of Music displayed on the touchscreen  300 , the application option  614  of Gallery corresponds to an application interface  440  of Gallery displayed on the touchscreen  300 , and the application option  615  of Messages corresponds to an application interface  450  of Messages displayed on the touchscreen  300 . The OK button  616  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation, the electronic device  100  may project an application interface selected by the user onto the display of the external display device  200 . The cancel button  617  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation, the electronic device  100  may cancel projection of an application interface selected by the user onto the display of the external display device  200  for displaying. The window close button  618  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation, the electronic device  100  may close the application selection window  610 . 
     Each application option has a marker, and the marker may be used to prompt the user whether the application option is selected. When the marker is in a disabled state, the application option is not selected, and when the marker is in an enabled state, the application option is selected. For example, as shown in  FIG. 6A-1  and  FIG. 6A-2 , there is a marker  621  on the application option  611  of Video, a marker  622  on the application option  612  of Settings, a marker  623  on the application option  613  of Music, a marker  624  on the application option  614  of Gallery, and a marker  625  on the application option  615  of Messages. None of the application option  611  of Video, the application option  612  of Settings, the application option  613  of Music, the application option  614  of Gallery, and the application option  615  of Messages is selected. Therefore, the marker  621 , the marker  622 , the marker  623 , the marker  624 , and the marker  625  are all in a disabled state. 
     As shown in  FIG. 6B-1  and  FIG. 6B-2 , the electronic device  100  may receive a selection operation  631  by the user on the application option  611  of Video, and in response to the input operation  631 , the electronic device  100  may switch the marker  621  on the application option  611  of Video to an enabled state shown in  FIG. 6C-1  and  FIG. 6C-2 . The electronic device  100  may receive a selection operation  632  by the user on the application icon  612  of Settings, and in response to the input operation  632 , the electronic device  100  may switch the marker  622  on the application option  612  of Settings to an enabled state shown in  FIG. 6C-1  and  FIG. 6C-2 . The electronic device  100  may receive a selection operation  633  by the user on the application option  613  of Music, and in response to the input operation  633 , the electronic device  100  may switch the marker  623  on the application option  613  of Music to an enabled state shown in  FIG. 6C-1  and  FIG. 6C-2 . The electronic device  100  may receive a selection operation  634  by the user on the application option  614  of Gallery, and in response to the input operation  634 , the electronic device  100  may switch the marker  624  on the application option  614  of Gallery to an enabled state shown in  FIG. 6C-1  and  FIG. 6C-2 . 
     As shown in  FIG. 6C-1  and  FIG. 6C-2 , the electronic device  100  may receive an input operation  636  (for example, tapping) by the user on the OK button  616 . In response to the input operation  636 , the electronic device  100  may project application interfaces corresponding to application options selected by the user onto the display of the external display device  200 . For example, as shown in  FIG. 6C-1  and  FIG. 6C-2 , the application options selected by the user include the application option  611  of Video, the application option  612  of Settings, the application option  613  of Music, and the application option  614  of Gallery. Therefore, in response to the input operation  636  on the OK button  616 , the electronic device  100  may project the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 6D-1  and  FIG. 6D-2 , an application interface  510  of Video, an application interface  520  of Settings, an application interface  530  of Music, and an application interface  540  of Gallery are displayed on the display of the external display device  200 . Display content in the application interface  510  of Video is the same as display content in the application interface  410  of Video displayed on the touchscreen  300  of the electronic device  100 . Display content in the application interface  520  of Settings is the same as display content in the application interface  420  of Settings displayed on the touchscreen  300  of the electronic device  100 . Display content in the application interface  530  of Music is the same as display content in the application interface  430  of Music displayed on the touchscreen  300  of the electronic device  100 . Display content in the application interface  540  of Gallery is the same as display content in the application interface  440  of Video displayed on the touchscreen  300  of the electronic device  100 . Relative positions of the application interface  510  of Video, the application interface  520  of Settings, the application interface  530  of Music, and the application interface  540  of Gallery that are displayed on the display of the external display device  200  are the same as relative positions of the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery that are displayed on the touchscreen  300 . 
     In a possible implementation, a layout of the one or more application interfaces displayed on the display of the external display device  200  is different from a layout of the one or more application interfaces displayed on the touchscreen  300 . For details, refer to the embodiments shown in  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5F-1  and  FIG. 5F-2 . Details are not described herein again. 
     As shown in  FIG. 6D-1  and  FIG. 6D-2 , the electronic device  100  may receive an input operation  638  (for example, tapping) by the user on the window close button  618  in the application selection window  610 , and in response to the input operation  638 , the electronic device  100  may close the application selection window  610 , and display a shortcut button  641  on the touchscreen  300 . The shortcut button  641  may be in an upper left corner of the touchscreen  300 , or may be in another position on the touchscreen  300 . This is not limited herein. 
     As shown in  FIG. 6E-1  and  FIG. 6E-2 , the electronic device  100  may receive an input operation  642  (for example, tapping) by the user on the shortcut button  641 , and in response to the input operation  642 , as shown in  FIG. 6F-1  and  FIG. 6F-2 , the electronic device  100  may display the application selection window  610  on the touchscreen  300 . 
     In a possible implementation, after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the one or more application interfaces on the touchscreen  300 , the electronic device  100  may receive an input operation of the user, to cancel projection of one or more application interfaces onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 6F-1  and  FIG. 6F-2 , the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery are selected by the user and are projected onto the display of the external display device  200  for displaying. Therefore, the marker  621  on the application option  611  of Video, the marker  622  on the application option  612  of Settings, the marker  623  on the application option  613  of Music, and the marker  624  on the application option  614  of Gallery are all in an enabled state. The electronic device  100  may receive an input operation  644  (for example, tapping) by the user on the application option  614  of Gallery, and in response to the input operation  644 , the electronic device  100  may switch the marker  624  on the application option  614  of Gallery from the enabled state to a disabled state. 
     As shown in  FIG. 6G-1  and  FIG. 6G-2 , the electronic device  100  may receive an input operation  646  (for example, tapping) by the user on the OK button  616  in the application selection window  610 . In response to the input operation  646 , as shown in  FIG. 6H-1  and  FIG. 6H-2 , the electronic device  100  may cancel projection of the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 6H-1  and  FIG. 6H-2 , the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music are displayed on the display of the external display device  200 . The display content in the application interface  510  of Video is the same as the display content in the application interface  410  of Video displayed on the touchscreen  300  of the electronic device  100 . The display content in the application interface  520  of Settings is the same as the display content in the application interface  420  of Settings displayed on the touchscreen  300  of the electronic device  100 . The display content in the application interface  530  of Music is the same as display content in the application interface  430  of Music displayed on the touchscreen  300  of the electronic device  100 . Relative positions of the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music that are displayed on the display of the external display device  200  are the same as relative positions of the application interface  410  of Video, the application interface  420  of Settings, and the application interface  430  of Music that are displayed on the touchscreen  300 . 
     In a possible implementation, a layout of the one or more application interfaces displayed on the display of the external display device  200  is different from a layout of the one or more application interfaces displayed on the touchscreen  300 . For details, refer to the embodiments shown in  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5F-1  and  FIG. 5F-2 . Details are not described herein again. 
     In some application scenarios, a user needs to simultaneously process a plurality of application tasks on the electronic device  100 . To meet such a requirement of the user, the electronic device  100  may display a plurality of application interfaces (for example, an application interface of Video, an application interface of Settings, an application interface of Music, an application interface of Gallery, and an application interface of Messages) in different areas on the touchscreen  300 . When the plurality of application interfaces are displayed in different areas on the touchscreen  300  of the electronic device  100 , when the electronic device  100  receives an input operation of the user and enables a screen projection function, the electronic device  100  may establish a connection (for example, a wireless connection such as Wi-Fi or a wired connection) to the external display device  200 , and display a projection notification window on the touchscreen  300 . The projection notification window may be displayed by using a gesture operation (for example, swiping down from the top of the touchscreen  300 ) by the user. The projection notification window includes a plurality of application options, and the plurality of application options may be options of an icon type (for example, an application icon of Video, an application icon of Settings, an application icon of Music, an application icon of Gallery, an application icon of Messages) or may be options of a text type. This is not limited herein. Each of the plurality of application interfaces displayed in different areas on the touchscreen  300  corresponds to an application option in the projection notification window. The electronic device  100  may receive a selection operation that is performed by the user on the plurality of application options in the projection notification window. In response to the selection operation, the electronic device  100  may project, onto the display of the external display device  200 , one or more application interfaces corresponding to one or more application options selected by the user. In this way, the electronic device  100  can select, based on the input operation of the user, some application interfaces from the plurality of application interfaces split-screen displayed on the touchscreen  300 , and project the some application interfaces onto the display of the external display device  200 , to ensure that an application interface involving user privacy is projected only after the user agrees and confirms. This ensures user privacy. 
     For example, the electronic device  100  receives the input operation (for example, the input operation  472  on the projection device option  471  in  FIG. 4D-1  and  FIG. 4D-2 ) by the user. In response to the input operation of the user, the electronic device  100  may establish a connection to the external display device  200 , and display a window  460  and a projection notification window  710  shown in  FIG. 7A-1  and  FIG. 7A-2  on the touchscreen  300 . For text descriptions of the window  460 , refer to the embodiment shown in  FIG. 4C-1  and  FIG. 4C-2 . Details are not described herein again. 
     As shown in  FIG. 7A-1  and  FIG. 7A-2 , the projection notification window  710  includes a plurality of application options, an OK button  716 , and a cancel button  717 . For example, the projection notification window  710  includes an application option  711  of Video, an application option  712  of Settings, an application option  713  of Music, an application option  714  of Gallery, and an application option  715  of Messages. The application option  711  of Video corresponds to an application interface  410  of Video displayed on the touchscreen  300 , the application option  712  of Settings corresponds to an application interface  420  of Settings displayed on the touchscreen  300 , the application option  713  of Music corresponds to an application interface  430  of Music displayed on the touchscreen  300 , the application option  714  of Gallery corresponds to an application interface  440  of Gallery displayed on the touchscreen  300 , and the application option  715  of Messages corresponds to an application interface  450  of Messages displayed on the touchscreen  300 . The OK button  716  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation, the electronic device  100  may project an application interface selected by the user onto the display of the external display device  200 . The cancel button  717  may be used to receive an input operation (for example, tapping) by the user. In response to the input operation, the electronic device  100  may cancel projection of an application interface selected by the user onto the display of the external display device  200  for displaying. 
     Each application option has a marker, and the marker may be used to prompt the user whether the application option is selected. When the marker is in a disabled state, the application option is not selected, and when the marker is in an enabled state, the application option is selected. For example, as shown in  FIG. 7B-1  and  FIG. 7B-2 , there is a marker  721  on the application option  711  of Video, a marker  722  on the application option  712  of Settings, a marker  723  on the application option  713  of Music, a marker  724  on the application option  714  of Gallery, and a marker  725  on the application option  715  of Messages. None of the application option  711  of Video, the application option  712  of Settings, the application option  713  of Music, the application option  714  of Gallery, and the application option  715  of Messages is selected. Therefore, the marker  721 , the marker  722 , the marker  723 , the marker  724 , and the marker  725  are all in a disabled state. 
     As shown in  FIG. 7B-1  and  FIG. 7B-2 , the electronic device  100  may receive a selection operation  731  by the user on the application option  711  of Video, and in response to the input operation  731 , the electronic device  100  may switch the marker  721  on the application option  711  of Video to an enabled state shown in  FIG. 7C-1  and  FIG. 7C-2 . The electronic device  100  may receive a selection operation  732  by the user on the application icon  712  of Settings, and in response to the input operation  732 , the electronic device  100  may switch the marker  722  on the application option  712  of Settings to an enabled state shown in  FIG. 7C-1  and  FIG. 7C-2 . The electronic device  100  may receive a selection operation  733  by the user on the application option  713  of Music, and in response to the input operation  733 , the electronic device  100  may switch the marker  723  on the application option  713  of Music to an enabled state shown in  FIG. 7C-1  and  FIG. 7C-2 . The electronic device  100  may receive a selection operation  734  by the user on the application option  714  of Gallery, and in response to the input operation  734 , the electronic device  100  may switch the marker  724  on the application option  714  of Gallery to an enabled state shown in  FIG. 7C-1  and  FIG. 7C-2 . 
     As shown in  FIG. 7C-1  and  FIG. 7C-2 , the electronic device  100  may receive an input operation  736  (for example, tapping) by the user on the OK button  716 . In response to the input operation  736 , the electronic device  100  may project application interfaces corresponding to application options selected by the user onto the display of the external display device  200 . For example, as shown in  FIG. 7C-1  and  FIG. 7C-2 , the application options selected by the user include the application option  711  of Video, the application option  712  of Settings, the application option  713  of Music, and the application option  714  of Gallery. Therefore, in response to the input operation  736  on the OK button  716 , the electronic device  100  may project the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 7D-1  and  FIG. 7D-2 , an application interface  510  of Video, an application interface  520  of Settings, an application interface  530  of Music, and an application interface  540  of Gallery are displayed on the display of the external display device  200 . For details, refer to the embodiment shown in  FIG. 6D-1  and  FIG. 6D-2 . Details are not described herein again. 
     In a possible implementation, after the electronic device  100  exits displaying the projection notification window  710 , the electronic device  100  may receive a gesture operation (for example, swiping down from the top of the touchscreen  300 ) by the user. In response to the gesture operation, the electronic device  100  may display the projection notification window  710  again. 
     For example, as shown in  FIG. 7D-1  and  FIG. 7D-2 , the electronic device  100  has projected, onto the display of the external display device  200  for displaying, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery on the touchscreen  300 . The electronic device  100  may receive a gesture operation  751  (for example, swiping down from the top of the touchscreen  300 ) by the user on the touchscreen  300 . In response to the gesture operation  751 , as shown in  FIG. 7E-1  and  FIG. 7E-2 , the electronic device  100  may display the window  460  and the projection notification window  710  on the touchscreen  300 . 
     In a possible implementation, after the electronic device  100  projects, onto the display of the external display device  200  for displaying, the one or more application interfaces on the touchscreen  300 , the electronic device  100  may receive an input operation of the user, to cancel projection of one or more application interfaces onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 7E-1  and  FIG. 7E-2 , the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, and the application interface  440  of Gallery are selected by the user and are projected onto the display of the external display device  200  for displaying. Therefore, the marker  721  on the application option  711  of Video, the marker  722  on the application option  712  of Settings, the marker  723  on the application option  713  of Music, and the marker  724  on the application option  714  of Gallery are all in an enabled state. The electronic device  100  may receive an input operation  744  (for example, tapping) by the user on the application option  714  of Gallery, and in response to the input operation  744 , the electronic device  100  may switch the marker  724  on the application option  714  of Gallery from an enabled state to a disabled state. 
     As shown in  FIG. 7F-1  and  FIG. 7F-2 , the electronic device  100  may receive an input operation  746  (for example, tapping) by the user on the OK button  716  in the projection notification window  710 . In response to the input operation  746 , as shown in  FIG. 7G-1  and  FIG. 7G-2 , the electronic device  100  may cancel projection of the application interface  440  of Gallery onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 7G-1  and  FIG. 7G-2 , the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music are displayed on the display of the external display device  200 . For details, refer to the embodiment shown in  FIG. 6H-1  and  FIG. 6H-2 . Details are not described herein again. 
     In a possible implementation, a layout of the one or more application interfaces displayed on the display of the external display device  200  is different from a layout of the one or more application interfaces displayed on the touchscreen  300 . For details, refer to the embodiments shown in  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5F-1  and  FIG. 5F-2 . Details are not described herein again. 
     In some application scenarios, the electronic device  100  has currently displayed some application interfaces (for example, an application interface of Video, an application interface of Settings, and an application interface of Music) in different areas on the touchscreen  300 , and has projected one or more (for example, the application interface of Video, the application interface of Settings, and the application interface of Music) of these application interfaces onto the display of the external display device  200  for displaying. In this case, the electronic device  100  may receive an input operation of the user, open another application in response to the input operation, and then split-screen display an application interface (for example, an application interface of Gallery) of the another application and the some application interfaces (for example, the application interface of Video, the application interface of Settings, and the application interface of Music) on the touchscreen  300 . Because the electronic device  100  has enabled a screen projection function, when the electronic device  100  split screen displays the application interface (for example, the application interface of Gallery) of the another application on the touchscreen  300 , the electronic device  100  does not immediately project the application interface of the another application onto the display of the external display device  200  for displaying. After receiving the input operation of the user, in response to the input operation, the electronic may project the application interface of the other application onto the display of the external display device  200  for displaying. In this way, when the electronic device  100  has projected, onto the display of the external display device  200  for displaying, the one or more application interfaces split screen displayed on the touchscreen  300 , and when the electronic device  100  additionally displays an application interface on the touchscreen  300 , the electronic device  100  needs to project the added application interface only after receiving the user operation. In this way, only after the user confirms, the electronic device  100  can project, onto the display of the external display device  200 , the application interfaces split screen displayed on the touchscreen  200 , to protect user privacy. 
     For example, as shown in  FIG. 8A-1  and  FIG. 8A-2 , the electronic device  100  displays an application interface  810  of Video, an application interface  820  of Settings, and an application interface  830  of Music in different areas on the touchscreen  300 . In addition, the electronic device  100  has projected the application interface  810  of Video, the application interface  820  of Settings, and the application interface  830  of Music onto the display of the external display device  200  for displaying. An application interface  881  of Video, an application interface  882  of Settings, and an application interface  883  of Music are displayed on the display of the external display device  200 . Display content in the application interface  881  of Video is the same as display content in the application interface  810  of Video, display content in the application interface  882  of Settings is the same as display content in the application interface  820  of Settings, and display content in the application interface  883  of Music is the same as display content in the application interface  830  of Music. 
     As shown in  FIG. 8B-1  and  FIG. 8B-2 , the electronic device  100  may receive an input operation  861  (for example, swiping left from the right edge of the touchscreen  300 ) by the user. In response to the input operation  861 , as shown in  FIG. 8C-1  and  FIG. 8C-2 , the electronic device  100  may display a shortcut menu  870  on the touchscreen  300 . The shortcut menu  870  includes one or more application icons (for example, an application icon  871  of Gallery, an application icon of Messages, an application icon of QQ, and an application icon of WeChat). 
     The electronic device  100  may receive an input operation  872  (for example, tapping) by the user on the application icon  871  of Gallery. In response to the input operation  872 , the electronic device  100  may display, on the touchscreen  300 , an application interface of Gallery and the application interfaces that have been split screen displayed on the touchscreen  300 . 
     As shown in  FIG. 8D-1  and  FIG. 8D-2 , after responding to the input operation  872  on the application icon  871  of Gallery, the electronic device  100  may split-screen display an application interface  840  of Video, an application interface  820  of Settings, an application interface  830  of Music, and an application interface  850  of Gallery on the touchscreen. In this case, the electronic device  100  projects the application interface  840  of Video, the application interface  822  of Settings, and the application interface  830  of Music onto the display of the external display device  200  for displaying. As shown in  FIG. 8D-1  and  FIG. 8D-2 , an application interface  884  of Video, an application interface  882  of Settings, and an application interface  883  of Music are displayed in different areas on the display of the external display device  200 . 
     Display content in the application interface  884  of Video is the same as display content in the application interface  840  of Video. Display content in the application interface  840  of Video is the same as display content in the application interface  810  of Video shown in  FIG. 8C-1  and  FIG. 8C-2 , but a display ratio of the application interface  840  of Video is different from a display ratio of the application interface  810  of Video. A projection add button  851  may be displayed in an upper right corner of a display area (or may be another position in the display area) corresponding to the application interface  850  of Gallery. 
     The electronic device  100  may receive an input operation  852  (for example, tapping) by the user on the projection add button  851 . In response to the input operation  852 , as shown in  FIG. 8E-1  and  FIG. 8E-2 , the electronic device  100  may project the application interface  850  of Gallery, together with the application interface  840  of Video, the application interface  820  of Settings, and the application interface  830  of Music, onto the display of the external display device  200  for displaying. 
     As shown in  FIG. 8E-1  and  FIG. 8E-2 , the application interface  884  of Video, the application interface  882  of Settings, the application interface  883  of Music, and an application interface  884  of Gallery are displayed in different areas on the display of the external display device  200 . Display content in the application interface  885  of Gallery is the same as display content in the application interface  850  of Gallery. When projecting the application interface  850  of Gallery onto the display of the external display device  200  for displaying, the electronic device  100  may display a projection cancel button  853  in an upper right corner (or may be another position) of the display area in which the application interface  850  of Gallery is located on the touchscreen  300 . The projection cancel button  853  may be used to receive an input operation of the user. In response to the input operation that is performed by the user on the projection cancel button  853 , the electronic device  100  may cancel projection of the application interface  850  of Gallery onto the display of the external display device  200  for displaying. 
     In some application scenarios, the electronic device  100  has currently displayed some application interfaces (for example, an application interface of Video, an application interface of Settings, and an application interface of Music) in different areas on the touchscreen  300 , and has projected one or more (for example, the application interface of Video, the application interface of Settings, and the application interface of Music) of these application interfaces onto the display of the external display device  200  for displaying. In this case, the electronic device  100  may receive an input operation of the user, and in response to the input operation, adjust a display ratio of an application interface (for example, the application interface of Video) on the touchscreen  300 . The electronic device  100  may project, onto the display of the external display device  200  for displaying, the application interface obtained after the display ratio is adjusted. When the application interface obtained after the display ratio is adjusted is projected onto the display of the external display device  200  for displaying, a display ratio on the display is also adjusted. In this way, the user may adjust, on the electronic device  100 , a display ratio of an application interface that is projected onto the external display device  200  for displaying, so that the user can conveniently adjust a display effect of the interface of the application for projection, and user experience is improved. 
     For example, as shown in  FIG. 9A-1  and  FIG. 9A-2 , the electronic device  100  displays an application interface  910  of Video, an application interface  920  of Settings, and an application interface  930  of Music in different areas on the touchscreen  300 . In addition, the electronic device  100  has projected the application interface  910  of Video, the application interface  920  of Settings, and the application interface  930  of Music onto the display of the external display device  200  for displaying. An application interface  981  of Video, an application interface  982  of Settings, and an application interface  983  of Music are displayed on the display of the external display device  200 . Display content in the application interface  981  of Video is the same as display content in the application interface  910  of Video, display content in the application interface  982  of Settings is the same as display content in the application interface  920  of Video, and display content in the application interface  983  of Music is the same as display content in the application interface  930  of Music. 
     There are dividing lines at boundaries of the application interface  910  of Video, the application interface  920  of Settings, and the application interface  930  of Music on the touchscreen  300 . The dividing lines may be used to receive an input operation (sliding left or right or sliding up or down) by the user, to adjust a display ratio of an application interface (including a width ratio in the left-right direction or a height ratio in the top-to-bottom direction). For example, as shown in  FIG. 9A-1  and  FIG. 9A-2 , a dividing line  971  and a dividing line  972  divide the touchscreen  300  into three display areas. The application interface  910  of Video is displayed in a display area on the left of the dividing line  971 , and the application interface  920  of Settings and the application interface  930  of Music are displayed in two display areas on the right of the dividing line  971 . The two display areas on the right of the dividing line  971  are separated by the dividing line  972 . The application interface  920  of Settings is displayed in a display area on the right of the dividing line  971  and above the dividing line  972 , and the application interface  930  of Music is displayed in a display area on the right of the dividing line  971  and below the dividing line  972 . 
     The electronic device  100  may receive an input operation  953  (for example, dragging the dividing line  971  to slide left by a distance) by the user on the dividing line  971 . In response to the input operation  973 , the electronic device  100  may adjust a width ratio of the application interface  910  of Video to be decreased in the left-right direction, and also adjust width ratios of the application interface  920  of Settings and the application interface  930  of Music to be increased in the left-right direction. After the electronic device  100  adjusts a display ratio of an application interface that is being projected and that is displayed on the touchscreen  300 , a display ratio of an application interface displayed on the display of the external display device  200  is also adjusted. 
     As shown in  FIG. 9B-1  and  FIG. 9B-2 , the electronic device  100  displays an application interface  940  of Video, an application interface  950  of Settings, and an application interface  960  of Music in different areas on the touchscreen  300 . A left-right width of the application interface  940  of Video is smaller than a left-right width of the application interface  910  of Video, a left-right width of the application interface  950  of Settings is greater than a left-right width of the application interface  920  of Settings, and a left-right width of the application interface  960  of Music is greater than a left-right width of the application interface  930  of Music. An application interface  984  of Video, an application interface  985  of Settings, and an application interface  986  of Music are displayed in different areas on the display of the external display device  200 . A left-right width of the application interface  984  of Video is smaller than a left-right width of the application interface  981  of Video, a left-right width of the application interface  985  of Settings is greater than a left-right width of the application interface  982  of Settings, and a left-right width of the application interface  986  of Music is greater than a left-right width of the application interface  983  of Music. 
     The following describes a screen projection method procedure when the electronic device  100  split screen displays a plurality of application interfaces in the conventional technology. 
       FIG. 10  is a schematic flowchart of a screen projection method according to a miracast protocol in the conventional technology. As shown in  FIG. 10 , an example in which the electronic device  100  displays five application interfaces in different areas on the touchscreen  300  is used for description. 
     1. The electronic device  100  obtains and synthesizes layers of all applications (an application  1 , an application  2 , an application  3 , an application  4 , and an application  5 ) displayed on the touchscreen  300 , to obtain a final synthesized layer, and displays an image at the synthesized layer on the touchscreen  300 . A display effect of the image at the synthesized layer may be that the electronic device  100  displays five application interfaces in different areas on the touchscreen  300 . 
     2. After the electronic device  100  enables a screen projection function and establishes a connection to the external display device  200 , the electronic device  100  may compress the image at the synthesized layer of all the applications displayed on the touchscreen  300  and audio that is being played by the electronic device  100 . 
     A compression format of the image may be H.264, and the H.264 may also be referred to as MPEG-4 part 10, advanced video coding (MPEG-4 part 10, advanced video coding, MPEG-4 AVC). The electronic device  100  may compress the captured audio, where a compression format of the audio may be advanced audio coding (AAC). 
     3. The electronic device  100  mixes the compressed image in H.264 format and the compressed audio in AAC format into a transport stream (transport stream, TS) file, and transmits the TS file to the external display device  200  over Wi-Fi P2P by using a real-time streaming protocol (RTSP). 
     4. The external display device  200  may receive the TS file by using the real-time streaming protocol, and perform audio and video decoding on the TS file, to obtain an image stream of the synthesized layer and the audio from the TS file through decoding. 
     5. The external display device  200  may display the image at the synthesized layer on the display of the external display device  200 . The five application interfaces (for example, an interface of the application  1 , an interface of the application  2 , an interface of the application  3 , an interface of the application  4 , and an interface of the application  5 ) are displayed on the display of the external display device  200 . The external display device  200  may play the decoded audio by using an output apparatus of the external display device  200 . 
     It can be learned from the foregoing that, when the electronic device  100  split-screen displays a plurality of application interfaces on the touchscreen  300 , after the electronic device  100  enables the screen projection function, the electronic device  100  can only project, onto the display of the external display device  200  for displaying, all the application interfaces split-screen displayed on the touchscreen  300 , and cannot project, onto the display of the external display device  200  for displaying, some selected application interfaces on the touchscreen  300 . In this way, some application interfaces involving user privacy are also projected onto the display of the external display device  200  for displaying. This easily causes leakage of user privacy. 
     The following describes a screen projection method provided in the embodiments of this application. 
       FIG. 11  is a schematic flowchart of a screen projection method according to an embodiment of this application. As shown in  FIG. 11 , an example in which the electronic device  100  displays five application interfaces in different areas on the touchscreen  300  is used for description. For example, an application  1  may be Video, an application  2  may be Settings, an application  3  may be Music, an application  4  may be Gallery, and an application  5  may be Messages. As shown in  FIG. 11 , the method may include the following steps. 
     1. The electronic device  100  obtains and synthesizes layers of the five applications (Video, Settings, Music, Gallery, and Messages), to obtain a final synthesized layer, and displays an image at the synthesized layer on the touchscreen  300 . A display effect of the image at the synthesized layer may be that the electronic device  100  displays the five application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, the application interface  440  of Gallery, and the application interface  450  of Messages in  FIG. 4A-1  and  FIG. 4A-2 ) in different areas on the touchscreen  300 . 
     2. After the electronic device  100  enables a screen projection function and establishes a connection to the external display device  200 , the electronic device  100  may capture the synthesized layer and audio that is being played by the electronic device  100 . The electronic device  100  may compress the image at the synthesized layer. A compression format of the image at the synthesized layer may be H.264. The electronic device  100  may compress the captured audio, where a compression format of the audio may be advanced audio coding (advanced audio coding, AAC). 
     The compression format of the image is not limited to the H.264 format, or may be another image compression format. This is not limited herein. The compression format of the audio is not limited to the AAC format, or may be another audio compression format. This is not limited herein. 
     3. The electronic device  100  mixes a compressed image file and a compressed audio file into a transport stream (TS) file, and transmits the TS file to the external display device  200  over a Wi-Fi P2P network by using a real-time streaming protocol (RTSP). 
     The electronic device  100  and the external display device  200  may be connected over the Wi-Fi P2P network, or may be connected over a wired network. This is not limited herein. A protocol used to transmit the TS file by the electronic device  100  is not limited to the RTSP protocol, or may be another protocol. This is not limited herein. 
     4. The electronic device  100  may receive an input (for example, a combination operation of the input operation  412  on the projection add button  411  in  FIG. 4E-1  and  FIG. 4E-2 , the input operation  422  on the projection add button  421  in  FIG. 4F-1  and  FIG. 4F-2 , and the input operation  432  on the projection add button  431  in  FIG. 4G-1  and  FIG. 4G-2 ) of selecting an application for projection by the user. In response to the input of selecting an application for projection, the electronic device  100  may obtain application window information of applications for projection (for example, Video, Settings, and Music). For example, the electronic device  100  may obtain the application window information of the applications for projection by using a window manager service (WMS). After obtaining the application window information of the applications for projection, the electronic device  100  may send the application window information of the applications for projection to the external display device  200 . 
     The application window information includes information such as a window position, a window size, and a window level of the application for projection. For example, as shown in  FIG. 4A-1  and  FIG. 4A-2 , a window of Video is on the left on the touchscreen  300 , a height of the window is the same as that of the touchscreen  300 , a width of the window is one-third of a width of the touchscreen  300 , and a level of the window is 22. The example is merely used to explain this application and shall not constitute a limitation. 
     5. The external display device  200  may receive the TS file by using the real-time streaming protocol, and perform audio and video decoding on the TS file, to obtain the image at the synthesized layer and the audio from the TS file through decoding. 
     6. The external display device  200  may crop, from the image at the synthesized layer based on the received application window information of the applications for projection, image areas in which windows of the applications for projection (for example, Video, Settings, and Music) are located, and splice these image areas, to synthesize into a to-be-projected image. The to-be-projected image includes window interfaces of the applications for projection (for example, Video, Settings, and Music). 
     7. The external display device  200  may display the projected image on the display of the external display device  200 . At the same time, the external display device  200  may play the decoded audio by using an output apparatus. 
     For example, as shown in  FIG. 4H-1  and  FIG. 4H-2 , the projected image is displayed on the display of the external display device  200 . The projected image includes the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music. 
     In a possible case, a layout of the one or more application interfaces displayed on the display of the external display device  200  is different from a layout of the one or more application interfaces displayed on the touchscreen  300 . In other words, before projecting, onto the external display device  200 , the one or more application interfaces displayed on the touchscreen  300 , the electronic device  100  may change relative positions of the one or more application interfaces displayed on the display of the external display device  200 , splice, into one to-be-projected image, the one or more application interfaces obtained after the layout is changed, and send the to-be-projected image to the external display device  200 . The external display device  200  displays, on the display, the one or more application interfaces obtained after the layout is changed. For details, refer to the embodiments shown in  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5E-1  and  FIG. 5E-2 . Details are not described herein again. 
     In this embodiment of this application, when the electronic device  100  displays the plurality of application interfaces in different areas on the touchscreen  300 , the electronic device  100  obtains the application window information of the applications for projection selected by the user, and sends the application window information and the synthesized image of the plurality of application interfaces to the external display device  200 . The application window information includes information such as a window position, a window size, and a window level of the application for projection. After receiving the application window information and the synthesized image of the plurality of application interfaces, the external display device  200  may crop interface images of the one or more applications for projection from the synthesized image based on the application window information, splice the interface images of the one or more applications for projection, and then display a spliced image on the display. In this way, the electronic device  100  can project, onto the display of the external display device  200 , some of the plurality of application interfaces split screen displayed on the touchscreen  300 . The screen projection method provided in this embodiment of this application ensures that an application interface that involves user privacy is projected only after the user agrees and confirms, and ensures user privacy. 
       FIG. 12  is a schematic flowchart of a screen projection method according to another embodiment of this application. As shown in  FIG. 12 , an example in which the electronic device  100  displays five application interfaces in different areas on the touchscreen  300  is used for description. For example, an application  1  may be Video, an application  2  may be Settings, an application  3  may be Music, an application  4  may be Gallery, and an application  5  may be Messages. As shown in  FIG. 12 , the method may include the following steps. 
     1. The electronic device  100  obtains and synthesizes layers of the five applications (Video, Settings, Music, Gallery, and Messages), to obtain a final synthesized layer, and displays an image at the synthesized layer on the touchscreen  300 . A display effect of the image at the synthesized layer may be that the electronic device  100  displays the five application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, the application interface  440  of Gallery, and the application interface  450  of Messages in  FIG. 4A-1  and  FIG. 4A-2 ) in different areas on the touchscreen  300 . 
     2. After the electronic device  100  enables a screen projection function and establishes a connection to the external display device  200 , the electronic device  100  may receive an input (for example, a combination operation of the input operation  412  on the projection add button  411  in  FIG. 4E-1  and  FIG. 4E-2 , the input operation  422  on the projection add button  421  in  FIG. 4F-1  and  FIG. 4F-2 , and the input operation  432  on the projection add button  431  in  FIG. 4G-1  and  FIG. 4G-2 ) of selecting an application for projection by the user. In response to the input of selecting an application for projection, the electronic device  100  may capture layers of the applications for projection (for example, Video, Settings, and Music) and obtain image streams of the applications for projection from the layers of the applications for projection. Then, the electronic device  100  may synthesize image streams of the plurality of applications for projection into one image stream. The electronic device  100  may capture and compress audio that is being played by the electronic device  100 . 
     For example, the applications for projection may include Video, Settings, and Music, and the electronic device  100  may capture a layer of Video, a layer of Settings, and a layer of Music. Then, the electronic device  100  obtains an image stream of Video from the layer of Video, obtains an image stream of Settings from the layer of Settings, and obtains an image stream of Music from the layer of Music. Then, the electronic device  100  may synthesize the image stream of Video, the image stream of Settings, and the image stream of Music into one image stream, and perform image stream compression on the synthesized image stream. The example is merely used to explain this application and shall not constitute a limitation. 
     A compression format of the image may be H.264, but is not limited to H.264, or may be another image compression format. A compression format of the audio may be advanced audio coding (AAC), but is not limited to the AAC format, or may be another audio compression format. 
     3. The electronic device  100  mixes the compressed image in H.264 format and compressed audio in AAC format into a transport stream (TS) file, and transmits the TS file to the external display device  200  over a Wi-Fi P2P network by using a real-time streaming protocol (RTSP). 
     The electronic device  100  and the external display device  200  may be connected over the Wi-Fi P2P network, or may be connected over a wired network. This is not limited herein. A protocol used to transmit the TS file by the electronic device  100  is not limited to the RTSP protocol, or may be another protocol. This is not limited herein. 
     4. The external display device  200  may receive the TS file by using the real-time streaming protocol, and perform audio and video decoding on the TS file, to obtain the synthesized image stream and the audio from the TS file through decoding. 
     5. The external display device  200  may obtain, through parsing, the image streams (for example, the image stream of Video, the image stream of Settings, and the image stream of Music) of the plurality of applications for projection from the synthesized image stream. 
     6. The external display device  200  may display the obtained image streams of the plurality of applications for projection in respective windows (which may also be referred to as display areas) corresponding to the applications for projection on the display. For example, the external device  200  may display the image stream of Video in a window  1  on the display, display the image stream of Settings in a window  2  on the display, and display the image stream of Music in a window  3  on the display. At the same time, the external display device  200  may play the decoded audio by using an output apparatus. 
     The external display device  200  may divide, according to a quantity of applications for projection, the display into windows (which may also be referred to as display areas) of a quantity the same as the quantity of applications for projection. In a possible case, a window position of each application for projection on the display of the external display device  200  may be the same as a window position of each application for projection on the touchscreen  300  of the electronic device  100 . For details, refer to  FIG. 4F-1  and  FIG. 4F-2  to  FIG. 4I-1  and  FIG. 4I-2 . Details are not described herein again. 
     In a possible case, a window position of each application for projection on the display of the external display device  200  may be different from a window position of each application for projection on the touchscreen  300  of the electronic device  100 . For details, refer to  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5F-1  and  FIG. 5F-2 . Details are not described herein again. 
     In this embodiment of this application, when the electronic device  100  displays the plurality of application interfaces in different areas on the touchscreen  300 , the electronic device  100  captures the layers of the applications for projection selected by the user, and obtains the image streams of the applications for projection. Then, the electronic device  100  may synthesize the image streams of the applications for projection into one image stream. The electronic device  100  sends the compressed image stream to the external display device  200 . After receiving the synthesized image stream, the external display device  200  may parse the synthesized image stream to obtain the image stream of each application for projection, and display the image stream in the corresponding window of each application for projection. In this way, the electronic device  100  can project, onto the display of the external display device  200 , some of the plurality of application interfaces split screen displayed on the touchscreen  300 . The screen projection method provided in this embodiment of this application ensures that an application interface that involves user privacy is projected only after the user agrees and confirms, and ensures user privacy. 
       FIG. 13  is a schematic flowchart of a screen projection method according to another embodiment of this application. As shown in  FIG. 13 , an example in which the electronic device  100  displays five application interfaces in different areas on the touchscreen  300  is used for description. For example, an application  1  may be Video, an application  2  may be Settings, an application  3  may be Music, an application  4  may be Gallery, and an application  5  may be Messages. As shown in  FIG. 13 , the method may include the following steps. 
     1. The electronic device  100  obtains and synthesizes layers of the five applications (Video, Settings, Music, Gallery, and Messages), to obtain a final synthesized layer, and displays an image at the synthesized layer on the touchscreen  300 . A display effect of the image at the synthesized layer may be that the electronic device  100  displays the five application interfaces (for example, the application interface  410  of Video, the application interface  420  of Settings, the application interface  430  of Music, the application interface  440  of Gallery, and the application interface  450  of Messages in  FIG. 4A-1  and  FIG. 4A-2 ) in different areas on the touchscreen  300 . 
     2. After the electronic device  100  enables a screen projection function and establishes a connection to the external display device  200 , the electronic device  100  may capture the synthesized layer and audio that is being played by the electronic device  100 . 
     3. The electronic device  100  may receive an input (for example, a combination operation of the input operation  412  on the projection add button  411  in  FIG. 4E-1  and  FIG. 4E-2 , the input operation  422  on the projection add button  421  in  FIG. 4F-1  and  FIG. 4F-2 , and the input operation  432  on the projection add button  431  in  FIG. 4G-1  and  FIG. 4G-2 ) of selecting an application for projection by the user. In response to the input of selecting an application for projection, the electronic device  100  may obtain application window information of applications for projection (for example, Video, Settings, and Music). For example, the electronic device  100  may obtain the application window information of the applications for projection by using a window manager service (window manager service, WMS). 
     The application window information includes information such as a window (which may also be referred to as a window interface of an application) position, a window size, and a window level of the application for projection. For example, as shown in  FIG. 4A-1  and  FIG. 4A-2 , a window of Video is on the left on the touchscreen  300 , a height of the window is the same as that of the touchscreen  300 , a width of the window is one-third of a width of the touchscreen  300 , and a level of the window is 22. The example is merely used to explain this application and shall not constitute a limitation. 
     4. The electronic device  100  may crop, from the image at the synthesized layer based on the application window information, image areas in which windows of the applications for projection (for example, Video, Settings, and Music) are located, and splice these image areas, to synthesize into a to-be-projected image. The to-be-projected image includes window interfaces of the applications for projection (for example, Video, Settings, and Music). 
     5. The electronic device  100  may compress the to-be-projected image. A compression format of the to-be-projected image may be H.264. The electronic device  100  may compress the captured audio, where a compression format of the audio may be advanced audio coding (AAC). 
     The compression format of the to-be-projected image is not limited to the H.264 format, or may be another image compression format. This is not limited herein. The compression format of the audio is not limited to the AAC format, or may be another audio compression format. This is not limited herein. 
     6. The electronic device  100  mixes a compressed image file and a compressed audio file into a transport stream (TS) file, and transmits the TS file to the external display device  200  over a Wi-Fi P2P network by using a real-time streaming protocol (RTSP). 
     The electronic device  100  and the external display device  200  may be connected over the Wi-Fi P2P network, or may be connected over a wired network. This is not limited herein. A protocol used to transmit the TS file by the electronic device  100  is not limited to the RTSP protocol, or may be another protocol. This is not limited herein. 
     7. The external display device  200  may receive the TS file by using the real-time streaming protocol, and perform audio and video decoding on the TS file, to obtain the to-be-projected image and the audio from the TS file through decoding. 
     8. The external display device  200  may display the projected image on the display of the external display device  200 . At the same time, the external display device  200  may play the decoded audio by using an output apparatus. 
     For example, as shown in  FIG. 4H-1  and  FIG. 4H-2 , the projected image is displayed on the display of the external display device  200 . The projected image includes the application interface  510  of Video, the application interface  520  of Settings, and the application interface  530  of Music. 
     In this embodiment of this application, when the electronic device  100  displays the plurality of application interfaces in different areas on the touchscreen  300 , the electronic device  100  obtains the application window information of the applications for projection selected by the user, crops an image area of each application for projection from the synthesized image of the plurality of application interfaces based on the application window information, and then splices the image areas of the applications for projection to synthesize into the to-be-projected image. The electronic device  100  sends the to-be-projected image to the external display device  200 , and the external display device  200  may receive the to-be-projected image according to an existing miracast projection protocol process, and display the to-be-projected image on the display. In this way, the electronic device  100  can project, onto the display of the external display device  200 , some of the plurality of application interfaces split screen displayed on the touchscreen  300 . The screen projection method provided in this embodiment of this application ensures that an application interface that involves user privacy is projected only after the user agrees and confirms, and ensures user privacy. 
       FIG. 14  is a schematic flowchart of a screen projection method according to an embodiment of this application. 
     As shown in  FIG. 14 , the method may include the following steps. 
     S 1401 : An electronic device displays M application interfaces on a display of the electronic device. M is an integer greater than 1. 
     In an example of this application, the display of the electronic device is the touchscreen  300  in the foregoing embodiments. 
     For example, reference may be made to the embodiment shown in  FIG. 4A-1  and  FIG. 4A-2 . The electronic device displays five application interfaces in different areas on the touchscreen  300 . For details, refer to the embodiment shown in  FIG. 4A-1  and  FIG. 4A-2 . Details are not described herein again. 
     S 1402 : The electronic device receives a first selection operation, and determines N application interfaces based on the first selection operation, where the first selection operation is performed on the electronic device to determine the N application interfaces from the M application interfaces, and N is a positive integer less than or equal to M. 
     In a possible implementation, that the electronic device receives a first selection operation may specifically include: The electronic device receives a first input. In response to the first input, the electronic device displays M projection add controls on the display, where the M projection add controls one-to-one correspond to the M application interfaces. The electronic device receives a second input used by a user to trigger N of the M projection add controls. The electronic device determines, based on the second input, the N application interfaces selected by the user, and sends, to the external display device, first data used to display the N application interfaces. 
     For example, the first input may be the input operation  472  (for example, tapping) on the projection device option  471  in the embodiment shown in  FIG. 4D-1  and  FIG. 4D-2 . As shown in  FIG. 4E-1  and  FIG. 4E-2 , the electronic device may display one projection add control in each application interface on the touchscreen. The second input that triggers the projection add control may be the input operation on the projection add control  411  and/or the projection add control  421  and/or the projection add control  431  and/or the projection add control  441  and/or the projection add control  451  in  FIG. 4E-1  and  FIG. 4E-2 . After the projection add button is triggered by the user, the electronic device may project an application interface corresponding to the projection add button to an external display device for displaying. For details, refer to the embodiments shown in  FIG. 4E-1  and  FIG. 4E-2  to  FIG. 4I-2  and  FIG. 4I-2 . Details are not described herein again. 
     In a possible implementation, in response to the first input, the electronic device may display M projection add controls and an OK button on the display. After receiving a second input used by a user to trigger N of the M projection add controls, the electronic device may further receive a third input used by the user to trigger the OK button. The electronic device determines, based on the second input, the N application interfaces selected by the user. In response to the third input, the electronic device may send, to the external display device, the first data used to display the N application interfaces. In this way, the user can be prevented from accidentally touching a projection add control, to prevent the user from mistakenly projecting an application interface corresponding to the projection add control onto the external display device for displaying. This improves user experience. 
     For example, as shown in  FIG. 4E-1  and  FIG. 4E-2 , after the electronic device receives the input operation  412  (for example, tapping) on the projection add control  411 , the electronic device may further tap an OK button (which is not shown in  FIG. 4E-1  and  FIG. 4E-2 , a display position of the OK button on the display of the electronic device is not limited). In response to the tapping operation on the OK button, the electronic device projects the application interface  410  of Video corresponding to the projection add control  411  onto the external display device for displaying. 
     In a possible implementation, after any projection add control is triggered, the electronic device displays a projection cancel control corresponding to the projection add control, where the projection cancel control is used by the user to cancel projection of an application interface corresponding to the projection cancel control. The electronic device receives a fourth input used by the user to trigger the projection cancel control. In response to the fourth input, the electronic device stops sending, to the external display device, image data of the application interface corresponding to the projection cancel control. In this way, the electronic device can stop projection of an application interface onto the external display device at any time according to a user requirement, to improve user experience. 
     For example, as shown in  FIG. 4H-1 ,  FIG. 4H-2 ,  FIG. 4I-1 , and  FIG. 4I-2 , after the projection add control  441  is triggered, the electronic device may display the projection cancel control  443  corresponding to the projection add control  441 . As shown in  FIG. 4J-1  and  FIG. 4J-2 , after the projection cancel control  443  is triggered, the electronic device may stop projecting the application interface  440  of Gallery corresponding to the projection cancel control  443  onto the external display device for displaying. For details, refer to the embodiments shown in  FIG. 4H-1  and  FIG. 4H-2  to  FIG. 4J-1  and  FIG. 4J-2 . Details are not described herein again. 
     In a possible implementation, that the electronic device receives a first selection operation may specifically include: The electronic device receives a fifth input. In response to the fifth input, the electronic device displays a shortcut menu on the display, where the shortcut menu includes M options, and the M options one-to-one correspond to the M application interfaces. The electronic device receives a sixth input used to select N of the M options. The electronic device determines, based on the sixth input, the N application interfaces selected by a user, and sends, to the external display device, the first data used to display the N application interfaces. In this way, the electronic device can select, based on the input operation of the user, the one or more application interfaces from the plurality of application interfaces displayed on the display of the electronic device, and project the one or more application interfaces onto the external display device  200 , to ensure that an application interface involving user privacy is projected only after the user agrees and confirms. This ensures user privacy. 
     For example, the fifth input may be the input operation  472  on the projection device option  471  in  FIG. 4D-1  and  FIG. 4D-2 . The shortcut menu may be shown in the application selection window  610  in  FIG. 6A-1  and  FIG. 6A-2 . The application selection window  610  includes a plurality of application options. The five application options in the application selection window  610  one-to-one correspond to the five application interfaces displayed on the touchscreen  300 . The sixth input may be an input operation on the application option  611  of Video and/or the application option  612  of Settings and/or the application option  613  of Music and/or the application option  614  of Gallery and/or the application option  615  of Messages in  FIG. 6B-1  and  FIG. 6B-2 . In response to the sixth input, the electronic device may determine the N application interfaces selected by the user, and send, to the external display device, the first data used to display the N application interfaces. The foregoing examples are merely used to explain this application, and shall not constitute a limitation. 
     In a possible implementation, the shortcut menu may include the M options and an OK button. After the electronic device receives a sixth input used to select N of the M options, the electronic device may further receive a seventh input used by the user to trigger the OK button. The electronic device may determine, based on the sixth input, the N application interfaces selected by the user. In response to the seventh input, the electronic device may send, to the external display device, the first data used to display the N application interfaces. In this way, after the user selects the N options, the electronic device projects the N application interfaces corresponding to the N options onto the external display device for displaying only after the user confirms. This prevents the user from mistakenly selecting an application interface for projection, and ensures user privacy. 
     For example, as shown in  FIG. 6B-1 ,  FIG. 6B-2 ,  FIG. 6C-1 , and  FIG. 6C-2 , after receiving the sixth input (the input operation  631 , the input operation  632 , the input operation  633 , and the input operation  634 ) of selecting the N application options (the application option  611  of Video, the application option  612  of Settings, the application option  613  of Music, and the application option  614  of Gallery) by the user, the electronic device may further receive the seventh input (for example, tapping) by the user on the OK button  616 . In response to the seventh input on the OK button  616 , the electronic device may determine the N application interfaces selected by the user, and send, to the external display device, the first data used to display the N application interfaces. The foregoing examples are merely used to explain this application, and shall not constitute a limitation. 
     S 1403 : The electronic device sends the first data to the external device in response to the first selection operation. 
     In a possible implementation, the first data includes a to-be-projected image including the N application interfaces. Before the electronic device sends the first data to the external display device, the electronic device may further obtain a synthesized image of the M application interfaces and first display information (namely, the application window information in the embodiment shown in  FIG. 13 ) of the N application interfaces, where the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces. The electronic device crops the to-be-projected image from the synthesized image of the M application interfaces based on the first display information of the N application interfaces. For details, refer to the embodiment shown in  FIG. 13 . Details are not described herein again. 
     In a possible implementation, before the electronic device sends the first data to the external display device, the electronic device obtains a synthesized image of the M application interfaces and first display information (namely, the application window information in the embodiment shown in  FIG. 11 ) of the N application interfaces. The first data includes the synthesized image of the M application interfaces and the first display information of the N application interfaces, the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces, and the first display information is used by the external display device to crop, from the synthesized image of the M application interfaces, an image including the N application interfaces and display the image. For details, refer to the embodiment shown in  FIG. 11 . Details are not described herein again. 
     In a possible implementation, the first data includes respective image data streams of the N application interfaces, and is used by the external display device to display the N application interfaces in N display windows in a one-to-one correspondence. Before the electronic device sends the first data to the external display device, the electronic device may further obtain the respective image data streams of the N application interfaces. For details, refer to the embodiment shown in  FIG. 12 . Details are not described herein again. 
     S 1404 : The external display device displays the N application interfaces after receiving the first data. 
     For example, for displaying the N application interfaces by the external display device, refer to the foregoing embodiments shown in  FIG. 4F-1  and  FIG. 4F-2  to  FIG. 4I-1  and  FIG. 4I-2 , or refer to the foregoing embodiments shown in  FIG. 5B-1  and  FIG. 5B-2  to  FIG. 5F-1  and  FIG. 5F-2 . Details are not described herein again. 
     According to the screen projection method provided in this embodiment of this application, when a plurality of application interfaces are displayed on the display (namely, the touchscreen  300 ) of the electronic device, the electronic device may receive a selection operation of the user, and project one or more application interfaces selected by the user onto the external display device for displaying. In this way, the electronic device can project, based on the selection operation of the user onto the external display device for displaying, the one or more application interfaces selected by the user on the display of the electronic device. This ensures that an application interface involving user privacy is projected only after the user agrees and confirms, to ensure user privacy and improve user experience. 
     In a possible implementation, the first data includes a to-be-projected image including the N application interfaces. Before the electronic device sends the first data to the external display device, the electronic device may further obtain a synthesized image of the M application interfaces and first display information of the N application interfaces, where the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces. The electronic device crops the to-be-projected image from the synthesized image of the M application interfaces based on the first display information of the N application interfaces. 
     In a possible implementation, the first data includes the synthesized image of the M application interfaces and the first display information of the N application interfaces, the first display information includes sizes, positions, and display levels of respective display windows of the N application interfaces, and the first display information is used by the external display device to crop, from the synthesized image of the M application interfaces, an image including the N application interfaces and display the image. 
     Before the electronic device sends the first data to the external display device, the method further includes: 
     The electronic device obtains the synthesized image of the M application interfaces and the first display information of the N application interfaces. 
     In a possible implementation, the first data includes respective image data streams of the N application interfaces, and is used by the external display device to display the N application interfaces in N display windows in a one-to-one correspondence. Before the electronic device sends the first data to the external display device, the electronic device may further obtain the respective image data streams of the N application interfaces. 
     In a possible implementation, that the electronic device receives a first selection operation may specifically include: The electronic device receives a fifth input. In response to the fifth input, the electronic device displays a shortcut menu on the display, where the shortcut menu includes M options, and the M options one-to-one correspond to the M application interfaces. The electronic device receives a sixth input used to select N of the M options. In response to the fifth input, the electronic device determines the N application interfaces selected by the user, and sends, to the external display device, the first data used to display the N application interfaces. 
     In a possible implementation, the shortcut menu may include the M options and an OK button. After the electronic device receives the sixth input used to select N of the M options, the electronic device may further receive a seventh input on the OK button. In response to the seventh input, the electronic device may determine the N application interfaces selected by the user, and send, to the external display device, the first data used to display the N application interfaces. 
     In conclusion, the foregoing embodiments are merely intended for describing the technical solutions of this application, but not for limiting this application. Although this application is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features thereof, without departing from the scope of the technical solutions of the embodiments of this application.