android - 无法设置 MediaControllerCompat.TransportControls

Question

我正在尝试在通知按钮中设置 onclick 侦听器，但是当我按下按钮时，我收到如下错误：

java.lang.RuntimeException: Unable to start service unnion.neelay.test1.MediaService@6fec2a5 with Intent { act=beatbox.neelay.dummybeat.ACTION_PLAY flg=0x10000000 cmp=unnion.neelay.test1/.MediaService bnds=[455,632][519,696] }: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.media.session.MediaControllerCompat$TransportControls.play()' on a null object reference
                                                                     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3034)
                                                                     at android.app.ActivityThread.access$2200(ActivityThread.java:153)
                                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
                                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                     at android.os.Looper.loop(Looper.java:148)
                                                                     at android.app.ActivityThread.main(ActivityThread.java:5441)
                                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
                                                                  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.media.session.MediaControllerCompat$TransportControls.play()' on a null object reference
                                                                     at unnion.neelay.test1.MediaService.handleIncomingActions(MediaService.java:890)
                                                                     at unnion.neelay.test1.MediaService.onStartCommand(MediaService.java:202)
                                                                     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3017)
                                                                     at android.app.ActivityThread.access$2200(ActivityThread.java:153) 
                                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449) 
                                                                     at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                     at android.os.Looper.loop(Looper.java:148) 
                                                                     at android.app.ActivityThread.main(ActivityThread.java:5441) 
                                                                     at java.lang.reflect.Method.invoke(Native Method) 
                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) 
                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 

但早些时候它工作正常，这是错误中显示的方法。

private void handleIncomingActions(Intent playbackAction) {
    if (playbackAction == null || playbackAction.getAction() == null) return;

    String actionString = playbackAction.getAction();
    if (actionString.equalsIgnoreCase(ACTION_PLAY)) {
        transportControls.play();
    } else if (actionString.equalsIgnoreCase(ACTION_PAUSE)) {
        transportControls.pause();
    } else if (actionString.equalsIgnoreCase(ACTION_NEXT)) {
      //  transportControls.skipToNext();
        transportControls.skipToNext();
    } else if (actionString.equalsIgnoreCase(ACTION_PREVIOUS)) {
      //  transportControls.skipToPrevious();
        transportControls.skipToPrevious();
    } else if (actionString.equalsIgnoreCase(ACTION_STOP)) {
       // transportControls.stop();
        transportControls.stop();
    }
}

 public PendingIntent playbackAction(int actionNumber) {
    Intent playbackAction = new Intent(this, MediaService.class);
    switch (actionNumber) {
        case 0:
            // Play
            playbackAction.setAction(ACTION_PLAY);
            return PendingIntent.getService(this, actionNumber, playbackAction, 0);
        case 1:
            // Pause
            playbackAction.setAction(ACTION_PAUSE);
            return PendingIntent.getService(this, actionNumber, playbackAction, 0);
        case 2:
            // Next track
            playbackAction.setAction(ACTION_NEXT);
            return PendingIntent.getService(this, actionNumber, playbackAction, 0);
        case 3:
            // Previous track
            playbackAction.setAction(ACTION_PREVIOUS);
            return PendingIntent.getService(this, actionNumber, playbackAction, 0);
        case 4:
            playbackAction.setAction(Constants.ACTION.STOPFOREGROUND_ACTION);
            return PendingIntent.getService(this, actionNumber, playbackAction, 0);
        default:
            break;
    }
    return null;
}

任何我做错的建议都会有所帮助。我把这个方法称为view.setOnClickPendingIntent(R.id.btnPause, playbackAction(1)); 。我试图让它在锁屏中工作，这就是为什么我将通知更改为前台，因为之前我覆盖了onbackbutton，希望有人能提前帮助我。