[XPERIA X8 General] TAJ_Rocks:
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Screen size: Actual physical size, measured as the screen's diagonal.

For simplicity, Android groups all actual screen sizes into four generalized sizes: small, normal, large, and extra large.

Screen density

The quantity of pixels within a physical area of the screen; usually referred to as dpi (dots per inch). For example, a "low" density screen has fewer pixels within a given physical area, compared to a "normal" or "high" density screen.

For simplicity, Android groups all actual screen densities into four generalized densities: low, medium, high, and extra high.

Orientation:The orientation of the screen from the user's point of view. This is either landscape or portrait, meaning that the screen's aspect ratio is either wide or tall, respectively. Be aware that not only do different devices operate in different orientations by default, but the orientation can change at runtime when the user rotates the device.

Pixel Density:is a measurement of the resolution of devices in various contexts: typically computer displays, image scanners, and digital camera image sensors.

Density-Independent Pixel (dp):A virtual pixel unit that you should use when defining UI layout, to express layout dimensions or position in a density-independent way.

The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is the baseline density assumed by the system for a "medium" density screen. At runtime, the system transparently handles any scaling of the dp units, as necessary, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple: px = dp * (dpi / 160). For example, on a 240 dpi screen, 1 dp equals 1.5 physical pixels. You should always use dp units when defining your application's UI, to ensure proper display of your UI on screens with different densities.

Android Resolution:Android runs on a variety of devices that offer different screen sizes and densities. For applications, the Android system provides a consistent development environment across devices and handles most of the work to adjust each application's user interface to the screen on which it is displayed. At the same time, the system provides APIs that allow you to control your application's UI for specific screen sizes and densities, in order to optimize your UI design for different screen configurations. For example, you might want a UI for tablets that's different from the UI for handsets.

LDPI:Resources for low-density (ldpi) screens (~120dpi).

MDPI:Resources for medium-density (mdpi) screens (~160dpi).

HDPI:Resources for high-density (hdpi) screens (~240dpi).

XHDPI:Resources for extra high-density (xhdpi) screens (~320dpi).

NODPI:Resources for all densities. These are density-independent resources. The system does not scale resources tagged with this qualifier, regardless of the current screen's density.

TVDPI:Resources for screens somewhere between mdpi and hdpi; approximately 213dpi. This is not considered a "primary" density group. It is mostly intended for televisions and most apps shouldn't need it—providing mdpi and hdpi resources is sufficient for most apps and the system will scale them as appropriate. If you find it necessary to provide tvdpi resources, you should size them at a factor of 1.33*mdpi. For example, a 100px x 100px image for mdpi screens should be 133px x 133px for tvdpi.

Dex: Dalvik Executable. Compiled Android application code file. Android programs are compiled into .dex files, which are in turn zipped into a single .apk file on the device. .dex files can be created by automatically translating compiled applications written in the Java programming language.

Action:An action is a description of something that an Intent sender wants done. An action is a string value assigned to an Intent. Action strings can be defined by Android or by a third-party developer. For example, android.intent.action.VIEW for a Web URL, or com.example.rumbler.SHAKE_PHONE for a custom application to vibrate the phone.

Activity:An activity is a single screen in an application, with supporting Java code, derived from the Activity class. Most commonly, an activity is visibly represented by a full screen window that can receive and handle UI events and perform complex tasks, because of the Window it uses to render its window. Though an Activity is typically full screen, it can also be floating or transparent.

AndroidManifest.xml:Every application must have an AndroidManifest.xml file (with precisely that name) in its root directory of the source tree. The manifest presents essential information about the application to the Android system, information the system must have before it can run any of the application’s code.

Application:From a component perspective, an Android application consists of one or more activities, services, listeners, and intent receivers. From a source file perspective, an Android application consists of code, resources, assets, and a single manifest. During compilation, these files are packaged in a single file called an application package file (.apk).

Broadcast Receiver:An application class that listens for Intents that are broadcast, rather than being sent to a single target application/activity. The system delivers a broadcast Intent to all interested broadcast receivers, which handle the Intent sequentially.

Canvas:A drawing surface that handles compositing of the actual bits against a Bitmap or Surface object. It has methods for standard computer drawing of bitmaps, lines, circles, rectangles, text, and so on, and is bound to a Bitmap or Surface. Canvas is the simplest, easiest way to draw 2D objects on the screen. However, it does not support hardware acceleration, as OpenGL ES does. The base class is Canvas.

Content Provider:A data-abstraction layer that you can use to safely expose your application’s data to other applications. A content provider is built on the ContentProvider class, which handles content query strings of a specific format to return data in a specific format.

Data:The data partition on the device contains the user-related data, such as installed applications and settings for those apps, as well as your SQLite database containing Android settings and messages. Normally, the directory /data/app is off-limits through the ‘adb shell’ command, as well as other terminal applications that can run on the device, since this directory contains the apk files for apps. On a rooted phone, using the ‘su’ command will allow full access to this partition. This partition can be flashed using Fastboot or Nandroid.

DDMS: Dalvik Debug Monitor Service, a GUI debugging application included with the SDK. It provides screen capture, log dump, and process examination capabilities. If you are developing in Eclipse using the ADT Plugin, DDMS is integrated into your development environment.

Dialog:A floating window that that acts as a lightweight form. A dialog can have button controls only and is intended to perform a simple action (such as button choice) and perhaps return a value. A dialog is not intended to persist in the history stack, contain complex layout, or perform complex actions. Android provides a default simple dialog for you with optional buttons, though you can define your own dialog layout. The base class for dialogs is Dialog.

Drawable:A compiled visual resource that can be used as a background, title, or other part of the screen. A drawable is typically loaded into another UI element, for example as a background image. A drawable is not able to receive events, but does assign various other properties such as “state” and scheduling, to enable subclasses such as animation objects or image libraries. Many drawable objects are loaded from drawable resource files — xml or bitmap files that describe the image. Drawable resources are compiled into subclasses of android.graphics.drawable.

Flash Memory:Flash memory, also known as NAND memory, is nonvolatile – keeping information even when the device is off. Flash memory in the device is equivalent to the hard drive in a computer. This is where the device’s operating system (sometimes called firmware) and applications are stored. Flash memory is slower than RAM, but is (almost always) faster than SD cards.

Logcat:While in adb (see ADB), type in “adb logcat > logcat.txt”. This will help you when resolving issues and bugs. There are also tools in the market you can use for this, one of which is called aLogcat. It can show different categories (severity of errors ect.) too, which is something adb logcat cannot do.

Playstore(Old:Market):The market on Android is a place where you can purchase or download applications for your phone. When you download through the market, the installation process is transparent (as in you don’t have to deal with the APK files yourself), and there is the facility to rate apps and post comments which are visible to other users. Frequently, the developers of apps actually take onboard the feedback in the comments (mainly the smaller apps with slightly less feedback to sift through).

When an app is installed from the market, it is copied to ‘/data/app/apkname.apk’, as the act of ‘installing’. An app can store its data in the folder ‘/data/data/apkname’. It is possible to clear the data stored by an application by using the Manage Applications feature in Settings | Applications | Manage Applications.

Intent:A message object that you can use to launch or communicate with other applications/activities asynchronously. An Intent object is an instance of Intent. It includes several criteria fields that you can supply, to determine what application/activity receives the Intent and what the receiver does when handling the Intent. Available criteria include the desired action, a category, a data string, the MIME type of the data, a handling class, and others. An application sends an Intent to the Android system, rather than sending it directly to another application/activity. The application can send the Intent to a single target application or it can send it as a broadcast, which can in turn be handled by multiple applications sequentially. The Android system is responsible for resolving the best-available receiver for each Intent, based on the criteria supplied in the Intent and the Intent Filters defined by other applications.

Intent Filter:A message object that you can use to launch or communicate with other applications/activities asynchronously. An Intent object is an instance of Intent. It includes several criteria fields that you can supply, to determine what application/activity receives the Intent and what the receiver does when handling the Intent. Available criteria include the desired action, a category, a data string, the MIME type of the data, a handling class, and others. An application sends an Intent to the Android system, rather than sending it directly to another application/activity. The application can send the Intent to a single target application or it can send it as a broadcast, which can in turn be handled by multiple applications sequentially. The Android system is responsible for resolving the best-available receiver for each Intent, based on the criteria supplied in the Intent and the Intent Filters defined by other applications.

Layout Resource:An XML file that describes the layout of an Activity screen.

Manifest File:An XML file that each application must define, to describe the application’s package name, version, components (activities, intent filters, services), imported libraries, and describes the various activities, and so on.

9-Patch:A resizeable bitmap resource that can be used for backgrounds or other images on the device.

Odex: Odex stands for “Optimized Dalvik Executable” file. The Android system, as identified above, utilizes compressed data stored in the .apk file at runtime. To speed up this process, the most critical elements of application will be placed uncompressed in an .odex file, thus enabling the Android OS to quickly interpret that important information before it continues to parse the rest of the application. Stock ROMs will come from the manufacturer as “odexed”, meaning that the application(s) will have a .apk file and an .odex file, i.e. Calendar.apk and Calendar.odex.

Resources:Nonprogrammatic application components that are external to the compiled application code, but which can be loaded from application code using a well-known reference format. Android supports a variety of resource types, but a typical application’s resources would consist of UI strings, UI layout components, graphics or other media files, and so on. An application uses resources to efficiently support localization and varied device profiles and states. For example, an application would include a separate set of resources for each supported local or device type, and it could include layout resources that are specific to the current screen orientation (landscape or portrait). The resources of an application are always stored in the res/* subfolders of the project.

Service:An object of class Service that runs in the background (without any UI presence) to perform various persistent actions, such as playing music or monitoring network activity.

SPL:The Secondary Program Loader is a piece of bootcode that initiates the startup of the phone, displaying the initial splash screen for the device, and loading the initial files from ROM.

It checks to see if a button combination is pressed on bootup (such as that to enter Recovery Mode or the bootloader), and loads the relevant system software. If no special instruction is given by holding keys, the bootloader loads the normal system software by initializing the boot process from the boot partition.

Flashing your SPL is risky, as the process failing will probably result in a broken, or bricked phone, since the SPL is executed very early on in the boot process, and any error here will prevent access to the recovery or bootloader features.

If you do flash the SPL though, it unlocks the Carrier-ID CID from the device, essentially allowing any RUU to be installed to the device, and allows flashing alternative or custom bootscreens.

Surface:An object of type Surface representing a block of memory that gets composited to the screen. A Surface holds a Canvas object for drawing, and provides various helper methods to draw layers and resize the surface. You should not use this class directly; use SurfaceView instead.

SurfaceView:A View object that wraps a Surface for drawing, and exposes methods to specify its size and format dynamically. A SurfaceView provides a way to draw independently of the UI thread for resource-intensive operations (such as games or camera previews), but it uses extra memory as a result. SurfaceView supports both Canvas and OpenGL ES graphics. The base class is SurfaceView.

System:The /system directory on your device is where the main operational software for the Android OS is stored. It has a number of sub-directories of which /system/apps (where application apk’s are stored) is probably the only one users would have need to access. The /system folder is read-only by default and needs remounted via ‘adb’ to allow write access.

Theme:A set of properties (text size, background color, and so on) bundled together to define various default display settings. Android provides a few standard themes, listed in R.style (starting with “Theme_”).

Update.zip:An update.zip (does not have to actually be called update.zip if you have a patched Recovery image) is a file containing some files which will be copied to the phone’s internal memory. Normally, a new system update or ROM is stored in the file, but update.zip files are commonly used to install modifications such as themes or applications that are installed on the System partition to prevent uninstallation.

To flash one of these files, which commonly would contain a custom ROM for your phone, you would boot your phone to a patched recovery image (whether using Fastboot, or the home+power method if you have a patched Recovery image flashed on your phone)

Update.zip files are cryptographically signed, and more information on how to sign your own files can be found online.

URI's:Android uses URI strings as the basis for requesting data in a content provider (such as to retrieve a list of contacts) and for requesting actions in an Intent (such as opening a Web page in a browser). The URI scheme and format is specialized according to the type of use, and an application can handle specific URI schemes and strings in any way it wants. Some URI schemes are reserved by system components. For example, requests for data from a content provider must use the content://. In an Intent, a URI using an http:// scheme will be handled by the browser.

View:An object that draws to a rectangular area on the screen and handles click, keystroke, and other interaction events. A View is a base class for most layout components of an Activity or Dialog screen (text boxes, windows, and so on). It receives calls from its parent object (see viewgroup, below)to draw itself, and informs its parent object about where and how big it would like to be (which may or may not be respected by the parent).

ViewGroup:A container object that groups a set of child Views. The viewgroup is responsible for deciding where child views are positioned and how large they can be, as well as for calling each to draw itself when appropriate. Some viewgroups are invisible and are for layout only, while others have an intrinsic UI (for instance, a scrolling list box). Viewgroups are all in the widget package, but extend ViewGroup.

Widget: One of a set of fully implemented View subclasses that render form elements and other UI components, such as a text box or popup menu. Because a widget is fully implemented, it handles measuring and drawing itself and responding to screen events. Widgets are all in the android.widget package.

Window:In an Android application, an object derived from the abstract class Window that specifies the elements of a generic window, such as the look and feel (title bar text, location and content of menus, and so on). Dialog and Activity use an implementation of this class to render a window. You do not need to implement this class or use windows in your application.

Credits

Diablo67 for great information