bdls bdls - 5 months ago 53
Android Question

Override back button to act like home button

On pressing the back button, I'd like my application to go into the stopped state, rather than the destroyed state.

In the Android docs it states:


...not all activities have the behavior that they are destroyed when BACK is pressed. When the user starts playing music in the Music application and then presses BACK, the application overrides the normal back behavior, preventing the player activity from being destroyed, and continues playing music, even though its activity is no longer visible


How do I replicate this functionality in my own application?

I think there must be three possibilities...


  1. Capture the back button press (as below) and then call whatever method(s) the home button calls.

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK)) {
    Log.d(this.getClass().getName(), "back button pressed");
    }
    return super.onKeyDown(keyCode, event);
    }

  2. Capture the back button press and then spoof a home button press.

  3. Capture the back button press, then start an Activity of the home screen, effectively putting my application's Activity into the stopped state.



Edit:
I know about services and am using one in the application to which this problem is related. This question is specifically about putting the Activity into the stopped state rather than the destroyed state on pressing the back button.

Answer

Most of the time you need to create a Service to perform something in the background, and your visible Activity simply controls this Service. (I'm sure the Music player works in the same way, so the example in the docs seems a bit misleading.) If that's the case, then your Activity can finish as usual and the Service will still be running.

A simpler approach is to capture the Back button press and call moveTaskToBack(true) as follows:

// 2.0 and above
@Override
public void onBackPressed() {
    moveTaskToBack(true);
}

// Before 2.0
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {
        moveTaskToBack(true);
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

I think the preferred option should be for an Activity to finish normally and be able to recreate itself e.g. reading the current state from a Service if needed. But moveTaskToBack can be used as a quick alternative on occasion.

NOTE: as pointed out by Dave below Android 2.0 introduced a new onBackPressed method, and these recommendations on how to handle the Back button.