Various portable terminals such as smartphones, smart watches, smart glasses or tablet personal computers (PCs) have a message transmitting and receiving function in addition to a voice call function as a basic communication function.  The message transmitting and receiving function refers to a function of transmitting information constructed as text written on a portable terminal to another portable terminal, or receiving information constructed as text written on another portable terminal.  The function of transmitting and receiving a text message to and from a portable terminal may be referred to as a message service.  Examples of the message service are short message service (SMS), multimedia messaging service (MMS), and e-mail service. 
With the recent rapid widespread use of portable terminals, populations using message service are also rapidly increasing.  Message service is easy to use and allows quick transmission of content and repeated message transmission attempts even if a voice call is not possible.  Accordingly, message service is currently solidifying its place as a communication method next to voice calls. 
However, with the trend of making more compact portable terminals, space for a keyboard to write a text message in the portable terminals is being gradually reduced.  Thus, instead of using a physical keyboard, a method of receiving character inputs via keys of a virtual keyboard displayed on a touch screen has been developed by providing a virtual keyboard to a user based on a touch screen. 
However, since the physical size of the hands and fingers of a user who uses a portable terminal cannot be reduced, the virtual keyboard displayed on the touch screen needs to have keys of a predetermined size or larger.  Thus, the virtual keyboard may also be a restrictive element in regard to manufacturing compact portable terminals.  In particular, it is difficult to provide a virtual keyboard on a touch screen in order to receive character inputs from a user, in a wearable device which has a relatively narrow space allocated for reception of a touch input from the user. 
Thus, a need exists for a method of allowing a user to write a text message quickly and accurately without using a keyboard on a wearable device and a wearable device for implementing the method. 
The above information is presented as background information only to assist with an understanding of the present disclosure.  No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.