Android: Prompt user to save changes when Back button is pressed

You’re not quite on the right track; what you should be doing is overriding onKeyDown() and listening for the back key, then overriding the default behavior:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
        // do something on back.
        return true;
    }

    return super.onKeyDown(keyCode, event);
}

If you’re only supporting Android 2.0 and higher, they’ve added an onBackPressed() you can use instead:

@Override
public void onBackPressed() {
    // do something on back.
    return;
}

This answer is essentially ripped from this blog post. Read it if you need long presses, compatibility support, support for virtual hard keys, or raw solutions like onPreIme() etc.