空对象引用上的Player $ OnAudioFocusChangedListener）'

Question

我正在构建一个音乐应用程序，它可以正常播放歌曲，但是最近，该应用程序将崩溃并显示错误：

尝试在空对象引用上调用接口方法'void vn.mymusic.android.store.media.player.Player.setOnAudioFocusChangedListener（vn.mymusic.android.store.media.player.Player $ OnAudioFocusChangedListener）'

这种错误很少发生，但我真的很想知道为什么原因以及解决方案。

    reset();
    releaseAudioEffectors();
    try {
        if (mPlayer == null) {
            mPlayer = mDetector.getPlayer(trackPath);
        }
    } catch (Exception e) {
    }

    if (mPlayer == null) {
        LogEx.d(TAG, "Player not found:" + trackPath);
        skipError();
        return;
    }
    mPlayer.setAudioFocusEnable(true);
    mPlayer.setOnAudioFocusChangedListener(this);
    mPlayer.setOnPreparedListener(this);
    mPlayer.setOnCompletionListener(this);
    mPlayer.setOnInfoListener(this);
    mPlayer.setOnErrorListener(this);
    mPlayer.setOnSeekCompleteListener(this);
    mPlayer.setNotificationIntentInfo(ACTION_PLAY, getPackageName(), PlayerFragment.class.getName(), Intent.FLAG_ACTIVITY_SINGLE_TOP);
    mPlayer.setWakeMode(PowerManager.PARTIAL_WAKE_LOCK);
    mPlayer.setOnMediaUpdatePlayCountListener(this);

OnAudioFocusChangeListener的替代方法

public void onAudioFocusChanged(int focusChange) {
    LogEx.d(TAG, "onAudioFocusChanged()" + focusChange);
    switch (focusChange) {
    case AudioManager.AUDIOFOCUS_LOSS:
    case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
    case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
        if (getStatus() == State.STARTED) {
            mPlayer.clearNotificationIntentInfo();

            mAudioFocusLoss = true;
            pause();
        }
        break;

    case AudioManager.AUDIOFOCUS_GAIN:
        if (mAudioFocusLoss) {
            mAudioFocusLoss = false;
            setAutoStart(true);
            start();
        }
        break;

    default:
        LogEx.e(TAG, "not handling audiofocus change :" + focusChange);
        break;
    }
}