Question

我正在尝试在后台播放音轨，以便在用户按下主页按钮时继续运行。

我的方法是使用Service，因为它似乎是实现此类行为的最佳方式。

我的代码分为活动和服务文件：

AudioPlaybackActivity.java

//....
Intent serviceIntent;
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.audio_playback_activity);
try
{
    serviceIntent = new Intent(this, AudioPlaybackService.class);
}catch (Exception e)
{
    e.printStackTrace();
}
}

  @Override
    public void onClick (View view)
    {
       switch (view.getId())
       {
           // ........
           case R.id.play:
           {
                try
                {
                 startService(serviceIntent); // Start the service when click on the play button
                }catch(Exception e)
               {
                   e.printStackTrace();
               }
               break;
           }
       }
    }

AudioPlaybackService.java ：

public class AudioPlaybackService extends Service implements MediaPlayer.OnCompletionListener,
        MediaPlayer.OnPreparedListener,
        MediaPlayer.OnErrorListener
{
    private MediaPlayer mediaPlayer;

    @Override
    public void onCreate()
    {

        mediaPlayer = new MediaPlayer();
        mediaPlayer.setOnPreparedListener(this);
        mediaPlayer.setOnCompletionListener(this);
        mediaPlayer.setOnErrorListener(this);
        mediaPlayer.reset();
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId)
    {
        if (!mediaPlayer.isPlaying())
        {
            mediaPlayer.reset();
            mediaPlayer = MediaPlayer.create(this.getApplicationContext(), R.raw.poi1);
            mediaPlayer.prepareAsync();
        }
        return START_STICKY;
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mediaPlayer != null)
        {
            if (mediaPlayer.isPlaying())
            {
                mediaPlayer.stop();
            }
            mediaPlayer.release();
        }
    }
    @Override
    public void onCompletion(MediaPlayer mp)
    {
        stopAudio();
        stopSelf(); // Stop the Service itself
    }
    @Override
    public void onPrepared(MediaPlayer arg0)
    {
        playAudio();
    }
    @Override
    public boolean onError(MediaPlayer mp, int what, int extra)
    {
        return false;
    }

    @Override
    public IBinder onBind(Intent arg0)
    {
        return null;
    }


    public void playAudio()
    {
        if (!mediaPlayer.isPlaying())
        {
            mediaPlayer.start();
        }
    }
    public void stopAudio()
    {
        if(mediaPlayer.isPlaying())
        {
           mediaPlayer.stop();
        }
    }

AndroidManifest.xml 文件：

//......... 
<service android:name="com.medigarage.audioguide.AudioPlaybackService"
        android:enabled="true">
</service>

每当我点击播放按钮启动音频播放时，应用程序崩溃。这是回溯：

09-23 20:41:11.960 32753-32753/com.xxxxx.xxxxx E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.xxxxx.xxxxxx, PID: 32753
  java.lang.RuntimeException: Unable to start service com.xxxxx.xxxxxx.AudioPlaybackService@42851838 with Intent { cmp=com.xxxx.xxxxxx/.AudioPlaybackService }: java.lang.IllegalStateException
  at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2872)
  at android.app.ActivityThread.access$2100(ActivityThread.java:155)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1341)
  at android.os.Handler.dispatchMessage(Handler.java:102)
  at android.os.Looper.loop(Looper.java:136)
  at android.app.ActivityThread.main(ActivityThread.java:5433)
  at java.lang.reflect.Method.invokeNative(Native Method)
  at java.lang.reflect.Method.invoke(Method.java:515)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
  at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalStateException
  at android.media.MediaPlayer.prepareAsync(Native Method)
  at com.xxxxx.xxxxxx.AudioPlaybackService.onStartCommand(AudioPlaybackService.java:35)
  at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2855)
  at android.app.ActivityThread.access$2100(ActivityThread.java:155) 
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1341) 
  at android.os.Handler.dispatchMessage(Handler.java:102) 
  at android.os.Looper.loop(Looper.java:136) 
  at android.app.ActivityThread.main(ActivityThread.java:5433) 
  at java.lang.reflect.Method.invokeNative(Native Method) 
  at java.lang.reflect.Method.invoke(Method.java:515) 
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268) 
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084) 
  at dalvik.system.NativeStart.main(Native Method)

为什么服务没有启动的任何想法？

Answer 1

您的问题是

mediaPlayer = MediaPlayer.create(this.getApplicationContext(), R.raw.poi1);
mediaPlayer.prepareAsync();

根据Android Docs for MediaPlayer.create()

为给定资源ID创建MediaPlayer的便捷方法。上成功，prepare（）已经被调用，绝不可以再次打电话。

致电mediaPlayer.prepareAsync()

后，您不应该致电MediaPlayer.create()

虽然如果您确实要异步准备MediaPlayer，可以直接设置数据源，而不是使用方便create()方法，如下所示：

mediaPlayer.setDataSource(getResources().openRawResourceFd(R.raw.poi1));

Answer 2

是。您的服务实际上正在启动，但媒体播放器已经准备就绪。

当您在本地播放文件时，请不要使用mediaPlayer.prepareAsync();，创建媒体播放器就像您自动准备播放器一样。只需删除mediaPlayer.prepareAsync();行即可。

编辑：

你可以这样做，但没有prepareAsync（）行，或者像这样：

1）将原始音频源的位置放入URI中，如下所示：

Uri UriOfFile = Uri.parse("android.resource://com.my.package/raw/audioFileName");

2）然后这段代码播放文件：

MediaPlayer mediaPlayer = new MediaPlayer();
mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mediaPlayer.setDataSource(getApplicationContext(), UriOfFile);
mediaPlayer.prepare(); // or prepareAsync()
mediaPlayer.start();

尝试使用服务在后台播放声音时的java.lang.IllegalStateException

2 个答案: