The two aspects of a UI are screen layout and event handling. Chapter 5, “User Interface Layout,” discussed how layouts are made up of
View objects, such as text and buttons. This chapter shows how to handle events from a user, such as physical key presses, touch events, and menu navigation. It also shows how to use a few advanced user interface libraries, namely, gestures and 3D graphics.
Most user interaction with an Android device is captured by the system and sent to a corresponding callback method. For example, if the physical BACK key is pressed, the
onBackPressed() method is called. Such events can be handled by extending the class and overriding the methods, called event handlers. ...