Android™ Application Development - Bahar Ali Khan

❑ onKeyUp Called when a user releases a pressed key
❑ onTrackballEvent Called when the device’s trackball is moved
Chapter 4: Creating User Interfaces
❑ onTouchEvent Called when the touch screen is pressed or released, or it detects movement
The following code snippet shows a skeleton class that overrides each of the user interaction handlers
in a View:
@Override
public boolean onKeyDown(int keyCode, KeyEvent keyEvent) {
// Return true if the event was handled.
return true;
}
@Override
public boolean onKeyUp(int keyCode, KeyEvent keyEvent) {
// Return true if the event was handled.
return true;
}
@Override
public boolean onTrackballEvent(MotionEvent event ) {
// Get the type of action this event represents
int actionPerformed = event.getAction();
// Return true if the event was handled.
return true;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// Get the type of action this event represents
int actionPerformed = event.getAction();
// Return true if the event was handled.
return true;
}
Further details on using each of these event handlers, including greater detail on the parameters
received by each method, are available in Chapter 11.
Creating a Compass View Example
In the following example, you’ll create a new Compass View by extending the View class. It uses a traditional
compass rose to indicate a heading/orientation. When complete, it should appear as in Figure 4-3.
A compass is an example of a User Interface control that requires a radically different visual display
from the textboxes and buttons available in the SDK toolbox, making it an excellent candidate for
building from scratch.
In Chapter 10, you’ll use this Compass View and the device’s built-in accelerometer to display the
user’s current bearing. Then in Chapter 11, you will learn some advanced techniques for Canvas drawing
that will let you dramatically improve its appearance.
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