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Handling Keyboard Actions

This lesson teaches you to

  1. Handle Single Key Events
  2. Handle Modifier Keys

When the user gives focus to an editable text view such as an EditText element and the user has a hardware keyboard attached, all input is handled by the system. If, however, you'd like to intercept or directly handle the keyboard input yourself, you can do so by implementing callback methods from the KeyEvent.Callback interface, such as onKeyDown() and onKeyMultiple().

Both the Activity and View class implement the KeyEvent.Callback interface, so you should generally override the callback methods in your extension of these classes as appropriate.

Note: When handling keyboard events with the KeyEvent class and related APIs, you should expect that such keyboard events come only from a hardware keyboard. You should never rely on receiving key events for any key on a soft input method (an on-screen keyboard).

Handle Single Key Events

To handle an individual key press, implement onKeyDown() or onKeyUp() as appropriate. Usually, you should use onKeyUp() if you want to be sure that you receive only one event. If the user presses and holds the button, then onKeyDown() is called multiple times.

For example, this implementation responds to some keyboard keys to control a game:

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    switch (keyCode) {
        case KeyEvent.KEYCODE_D:
            moveShip(MOVE_LEFT);
            return true;
        case KeyEvent.KEYCODE_F:
            moveShip(MOVE_RIGHT);
            return true;
        case KeyEvent.KEYCODE_J:
            fireMachineGun();
            return true;
        case KeyEvent.KEYCODE_K:
            fireMissile();
            return true;
        default:
            return super.onKeyUp(keyCode, event);
    }
}

Handle Modifier Keys

To respond to modifier key events such as when a key is combined with Shift or Control, you can query the KeyEvent that's passed to the callback method. Several methods provide information about modifier keys such as getModifiers() and getMetaState(). However, the simplest solution is to check whether the exact modifier key you care about is being pressed with methods such as isShiftPressed() and isCtrlPressed().

For example, here's the onKeyDown() implementation again, with some extra handling for when the Shift key is held down with one of the keys:

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    switch (keyCode) {
        ...
        case KeyEvent.KEYCODE_J:
            if (event.isShiftPressed()) {
                fireLaser();
            } else {
                fireMachineGun();
            }
            return true;
        case KeyEvent.KEYCODE_K:
            if (event.isShiftPressed()) {
                fireSeekingMissle();
            } else {
                fireMissile();
            }
            return true;
        default:
            return super.onKeyUp(keyCode, event);
    }
}
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