java - Android 音乐播放器无法从 onCreate 自动启动

Question

您好，我有音乐服务的实现代码，我想创建音乐播放器的演示，但它不会从 onCreate() 自动启动，我想在 Activity 打开时自动启动播放器。下面我放置了 Activity 和服务的代码，请帮助我，任何帮助将不胜感激。

public class MainActivity extends Activity {
    private ArrayList<Song> songList;
    private ListView songView;
    private MusicService musicSrv;
    private Intent playIntent;
    private boolean musicBound = false;
    private MusicController controller;
    private boolean paused = false, playbackPaused = false;
    private ServiceConnection musicConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            MusicService.MusicBinder binder = (MusicService.MusicBinder) service;
            musicSrv = binder.getService();
            musicSrv.setList(songList);
            musicBound = true;
        }
        @Override
        public void onServiceDisconnected(ComponentName name) {
            musicBound = false;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        songView = (ListView) findViewById(R.id.song_list);
        songList = new ArrayList<Song>();
        getSongList();
        Collections.sort(songList, new Comparator<Song>() {
            public int compare(Song a, Song b) {
                return a.getTitle().compareTo(b.getTitle());
            }
        });
        SongAdapter songAdt = new SongAdapter(this, songList);
        songView.setAdapter(songAdt);
songPicked();
    }
    @Override
    protected void onStart() {
        super.onStart();
        if (playIntent == null) {
            playIntent = new Intent(this, MusicService.class);
            bindService(playIntent, musicConnection, Context.BIND_AUTO_CREATE);
            startService(playIntent);
        }
    }
    public void songPicked() {
        musicSrv.setSong(0);
        musicSrv.playSong();
    }

    @Override
    protected void onPause() {
        super.onPause();
        paused = true;
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (paused) {
            paused = false;
        }
    }

    @Override
    protected void onStop() {
        controller.hide();
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        stopService(playIntent);
        musicSrv = null;
        super.onDestroy();
    }
}

下面我还放置了服务代码。

public class MusicService extends Service implements
        MediaPlayer.OnPreparedListener, MediaPlayer.OnErrorListener,
        MediaPlayer.OnCompletionListener {

    private final IBinder musicBind = new MusicBinder();
    private MediaPlayer player;
    private ArrayList<Song> songs;
    private int songPosn;
    private String songTitle = "";
    private Random rand;

    public void onCreate() {
        super.onCreate();
        songPosn = 0;
        rand = new Random();
        player = new MediaPlayer();
        initMusicPlayer();
    }

    public void initMusicPlayer() {
        player.setWakeMode(getApplicationContext(),
                PowerManager.PARTIAL_WAKE_LOCK);
        player.setAudioStreamType(AudioManager.STREAM_MUSIC);
        player.setOnPreparedListener(this);
        player.setOnCompletionListener(this);
        player.setOnErrorListener(this);
    }

    public void setList(ArrayList<Song> theSongs) {
        songs = theSongs;
    }

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

    @Override
    public boolean onUnbind(Intent intent) {
        player.stop();
        player.release();
        return false;
    }

    public void playSong() {
        player.reset();
        Song playSong = songs.get(0);
        songTitle = playSong.getTitle();
        long currSong = playSong.getID();
        Uri trackUri = ContentUris.withAppendedId(
                android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
                currSong);
        try {
            player.setDataSource(getApplicationContext(), trackUri);
        } catch (Exception e) {
            Log.e("MUSIC SERVICE", "Error setting data source", e);
        }
        try {
            player.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void setSong(int songIndex) {
        songPosn = songIndex;
    }

    @Override
    public void onCompletion(MediaPlayer mp) {
        if (player.getCurrentPosition() > 0) {
            mp.reset();
        }
    }

    @Override
    public boolean onError(MediaPlayer mp, int what, int extra) {
        mp.reset();
        return false;
    }

    @Override
    public void onPrepared(MediaPlayer mp) {
        mp.start();
        playSong();
    }

    @Override
    public void onDestroy() {
        stopForeground(true);
    }

    public class MusicBinder extends Binder {
        MusicService getService() {
            return MusicService.this;
        }
    }
}

我只想在应用程序自动启动时启动播放器，无需任何点击。但不幸的是，它显示因媒体播放器的空对象引用而停止。我从未使用过服务和音乐播放器。

由于音乐服务对象返回 null，因此引发空指针异常。

Answer 1

终于按照@vladMatvienko的回答解决了，感谢您的支持。

private ServiceConnection musicConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            MusicService.MusicBinder binder = (MusicService.MusicBinder) service;
            musicSrv = binder.getService();
            musicSrv.setList(songList);
            musicBound = true;
songPicked();
        }
        @Override
        public void onServiceDisconnected(ComponentName name) {
            musicBound = false;
        }
    };