当应用程序进入后台时停止 MediaPlayer 服务答案

【问题标题】：Stop MediaPlayer service when app goes in Background当应用程序进入后台时停止 MediaPlayer 服务
【发布时间】：2018-06-13 13:03:10
【问题描述】：

我有一个媒体播放器服务，可以在我的应用程序的后台播放音乐，例如：

public class Music extends Service {
MediaPlayer player;

@Override
public IBinder onBind(Intent intent) {
    return null;
}

public void onCreate() {
    player = MediaPlayer.create(this, R.raw.music);
    player.setLooping(true);
}

public int onStartCommand(Intent intent, int flags, int startId) {
    player.start();
    return Service.START_NOT_STICKY;
}


public void onDestroy() {
    player.stop();
    player.release();
    stopSelf();
    super.onDestroy();
}

问题是当用户更改应用程序或进入手机主屏幕（应用程序进入后台）时，音乐仍在播放。

我试图在 onStop 和 onDestroy 方法中停止它，但是当我更改我不想要的活动时，这会停止音乐（我希望在用户浏览活动时继续播放音乐） .

更新

我尝试过广播：

我加了

LocalBroadcastManager.getInstance(this).registerReceiver(StateReceiver, new IntentFilter("status"));

在音乐服务的onCreate和接收事件的方法中：

private BroadcastReceiver StateReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String status = intent.getStringExtra("status");
        if (parseInt(String.valueOf(status)) == 0) {
            player.stop();
        }else{player.start();}

    }
};

在应用程序类中我这样做了：

public class app_class extends Application implements Application.ActivityLifecycleCallbacks {
private static int resumed;
private static int paused;

private static String currentActivity;

@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
    currentActivity = activity.getClass().getSimpleName();
}
public static String getCurrentActivity() {
    return currentActivity;
}
@Override
public void onActivityStarted(Activity activity) {
}
 @Override
public void onActivityResumed(Activity activity) {
    send_status(1);
}

@Override
public void onActivityPaused(Activity activity) {
    send_status(0);
}  
 private void send_status(int status_counter) {
    Intent intent = new Intent("status");
    intent.putExtra("status", String.valueOf(status_counter));
    LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}
@Override
public void onActivityStopped(Activity activity) {      

}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

}
@Override
public void onActivityDestroyed(Activity activity) {

}

但音乐不会继续播放

【问题讨论】：

标签： java android service android-mediaplayer

【解决方案1】：

您需要在停止播放器后再次对其进行准备。如果您想在您的应用程序进入后台时停止播放，并在您的应用程序进入前台时从头开始播放媒体。只需将您的 BroadcastReceiver 代码修改为：

private BroadcastReceiver StateReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String status = intent.getStringExtra("status");
            if (parseInt(String.valueOf(status)) == 0) {
                player.stop();
            } else {
                player = MediaPlayer.create(this, R.raw.music);
                player.setLooping(true);
                player.start();
            }

        }
    };

但是，如果您想暂停播放并从您离开的地方继续播放，请进行以下更改：在您的 Application 类中，在 onActivityDestroyed() 中：

@Override
public void onActivityDestroyed(Activity activity) {
    send_status(2);
}

在广播接收器中：

private BroadcastReceiver StateReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String status = intent.getStringExtra("status");
            if (parseInt(String.valueOf(status)) == 0) {
                player.pause();  //When app is in background and not killed, we just want to pause the player and not want to lose the current state.
            } else if (parseInt(String.valueOf(status)) == 1) {
                if (player != null)
                    player.start();  // If the player was created and wasn't stopped, it won't be null, and the playback will be resumed from where we left of.
                else {
                    // If the player was stopped, we need to prepare it once again.
                    player = MediaPlayer.create(this, R.raw.music);
                    player.setLooping(true);
                    player.start();
                }
            } else if(player != null){
                player.stop();
                player.release();
            }

        }
    };

另外，看看MediaPlayer states。

【讨论】：

它只适用于一个不太重要的问题，但如果您知道任何修复方法，我们将不胜感激。当我浏览活动时，音乐会立即暂停和恢复，导致音乐瞬间失真。无论如何，我将标记为已纠正，因为我已经尝试找到一个星期的解决方案......所以非常感谢你

【解决方案2】：

您可以在您的应用程序类中添加它来检查您的应用程序是否在前台。

public class MyLifecycleHandler implements Application.ActivityLifecycleCallbacks {
    private static int resumed;
    private static int paused;
    private static int started;
    private static int stopped;

    private static String currentActivity;

    public static String getCurrentActivity() {
        return currentActivity;
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        currentActivity = activity.getClass().getSimpleName();
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

    @Override
    public void onActivityResumed(Activity activity) {
        ++resumed;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        ++paused;
        android.util.Log.w("test", "application is in foreground: " + (resumed > paused));

        // send broadcast from here to the service
        sendBroadcast()
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
    }

    @Override
    public void onActivityStarted(Activity activity) {
        ++started;
    }

    @Override
    public void onActivityStopped(Activity activity) {
        ++stopped;
        android.util.Log.w("test", "application is visible: " + (started > stopped));
    }

    public static boolean isApplicationVisible() {
        return started > stopped;
    }

    public static boolean isApplicationInForeground() {
        return resumed > paused;
    }
}

像这样将它添加到您的应用程序中：

public class MyApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();

        registerActivityLifecycleCallbacks(new MyLifecycleHandler());
    }
}

在服务中接收到广播后，您可以停止媒体播放器。

编辑

您需要将您的应用程序类更改为：

public class app_class extends Application implements Application.ActivityLifecycleCallbacks {
    private static int resumed;
    private static int paused;

    private static String currentActivity;

    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(this);
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        currentActivity = activity.getClass().getSimpleName();
    }
    public static String getCurrentActivity() {
        return currentActivity;
    }
    @Override
    public void onActivityStarted(Activity activity) {
    }
    @Override
    public void onActivityResumed(Activity activity) {
        send_status(1);
    }

    @Override
    public void onActivityPaused(Activity activity) {
        send_status(0);
    }
    private void send_status(int status_counter) {
        Intent intent = new Intent("status");
        intent.putExtra("status", String.valueOf(status_counter));
        LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
    }
    @Override
    public void onActivityStopped(Activity activity) {

    }
    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

    }
    @Override
    public void onActivityDestroyed(Activity activity) {

    }
}

【讨论】：

您能否再解释一下“在接收服务中的广播时，您可以停止媒体播放器。”
您可以从 MyLifecycleHandler 发送广播并在您的服务类中接收其广播。你可以在这里看到这个实现：stackoverflow.com/a/8875292/7384780
我想不通。它不会工作（音乐不会停止），但应用程序不会崩溃。
您需要在应用程序的 oncreate 中通过registerActivityLifecycleCallbacks(this) 注册ActivityLifecycleCallbacks。您是否能够在服务中接收广播？

【解决方案3】：

你实现了 onDestroy() 吗？如果没有，我相信这可能是解决方案 - 你停止你的 Player 或任何你用来在 onDestroy() 中运行服务的东西。

可以通过调用它的 stopSelf() 方法来停止服务，或者通过调用 Context.stopService()。

【讨论】：

【解决方案4】：

除了使用RoyalGriffin回答的广播接收器外，通过实现LifecycleObserver接口可以解决音乐中断少的问题。您可以知道应用程序处于前台还是后台，这样就无需处理每个活动的状态。

用他的方法在你的应用中实现Application.ActivityLifecycleCallbacks @OnLifecycleEvent(Lifecycle.Event.ON_STOP) 和 @OnLifecycleEvent(Lifecycle.Event.ON_START)

然后将这一行添加到 onCreate()

ProcessLifecycleOwner.get().getLifecycle().addObserver(this);

你的 app_class 应该是这样的：

    public class app_class extends Application implements LifecycleObserver, 
    Application.ActivityLifecycleCallbacks{
    private static int resumed;
    private static int paused;

    private static String currentActivity;

    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(this);
        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
    }

   @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    private void onAppBackgrounded() {
        Log.d(TAG, "App in background");
        send_status(0, this);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    private void onAppForegrounded() {
        Log.d(TAG, "App in foreground");
        send_status(1, this);
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle 
    savedInstanceState) {
        currentActivity = activity.getClass().getSimpleName();
    }
    public static String getCurrentActivity() {
        return currentActivity;
    }
    @Override
    public void onActivityStarted(Activity activity) {
    }
    @Override
    public void onActivityResumed(Activity activity) {
        //send_status(1);
    }

    @Override
    public void onActivityPaused(Activity activity) {
        //send_status(0);
    }
    private void send_status(int status_counter) {
        Intent intent = new Intent("status");
        intent.putExtra("status", String.valueOf(status_counter));
        LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
    }
    @Override
    public void onActivityStopped(Activity activity) {

    }
    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle 
    outState) {

    }
    @Override
    public void onActivityDestroyed(Activity activity) {

    }
}

【讨论】：

【解决方案5】：

LifecycleObserver 可以减少样板：

class App : Application(), LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onAppInBackground() {
        sendStatus(0)
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onAppInForeground() {
        sendStatus(1)
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onAppDestroyed() {
        sendStatus(2)
    }

    private fun sendStatus(statusCounter: Int) {
        val intent = Intent("status")
        intent.putExtra("status", statusCounter)
        LocalBroadcastManager.getInstance(this).sendBroadcast(intent)
    }

    override fun onCreate() {
        super.onCreate()
        ProcessLifecycleOwner.get().lifecycle.addObserver(this)
    }
}

添加到 build.gradle (app)

implementation "androidx.lifecycle:lifecycle-runtime:2.1.0"
implementation "androidx.lifecycle:lifecycle-extensions:2.1.0"
annotationProcessor "androidx.lifecycle:lifecycle-compiler:2.1.0"

【讨论】：