NumbersActivity.java

/**
 * This listener gets triggered whenever the audio focus changes
 * (i.e., we gain or lose audio focus because of another app or device).
 */
private AudioManager.OnAudioFocusChangeListener mOnAudioFocusChangeListener = new AudioManager.OnAudioFocusChangeListener() {
    @Override
    public void onAudioFocusChange(int focusChange) {
        if (focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT ||
                focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK) {
            // The AUDIOFOCUS_LOSS_TRANSIENT case means that we've lost audio focus for a