某些设备上未调用onAudioFocusChangeListener（）

Question

我将AudioFocus用于音乐播放器。它完美适用于华为P9 Lite（Android N）和华为P20 Lite（Android O）。但在三星Galaxy J3（2016）（Android L）上无法正常工作，似乎我没有请求音频焦点。

这就是我设置监听器的方式

mAudioFocusListener = new AudioManager.OnAudioFocusChangeListener() {
        @Override
        public void onAudioFocusChange(int focusChange) {
            switch (focusChange) {
                case AudioManager.AUDIOFOCUS_GAIN:
                    Log.i("AUDIOFOCUS", "AUDIOFOCUS_GAIN");
                    play();
                    break;
                case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT:
                    Log.i(TAG, "AUDIOFOCUS_GAIN_TRANSIENT");
                    break;
                case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK:
                    Log.i(TAG, "AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK");
                    break;
                case AudioManager.AUDIOFOCUS_LOSS:
                    Log.e(TAG, "AUDIOFOCUS_LOSS");
                    stop();
                    break;
                case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
                    Log.e(TAG, "AUDIOFOCUS_LOSS_TRANSIENT");
                    stop();
                    break;
                case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
                    Log.e(TAG, "AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK");
                    break;
                case AudioManager.AUDIOFOCUS_REQUEST_FAILED:
                    Log.e(TAG, "AUDIOFOCUS_REQUEST_FAILED");
                    break;
                default:

            }
        }
    };

这是请求方法

 private boolean requestAudioFocus() {
    if (!mAudioFocusGranted) {
        AudioManager am = (AudioManager) ctx.getSystemService(Context.AUDIO_SERVICE);
        if(am != null) {
            int result = am.requestAudioFocus(mAudioFocusListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);
            if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
                mAudioFocusGranted = true;
                Log.i("AUDIOFOCUS", "AUDIOFOCUS_GAIN");
            } else {
                //  failed
                Log.e(TAG, "Failed to get audio focus."); //todo
            }
        }else{
            //TODO
        }
    }
    return mAudioFocusGranted;
}

有没有人有任何想法？

编辑：我解决了将音频焦点请求放在主线程上的问题。