public class MusicService extends Service {

 public final IBinder binder = new MyBinder();
 public class MyBinder extends Binder{
 MusicService getService() {
 return MusicService.this;
 }
 }

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

private String[] musicDir = new String[]{
 Environment.getExternalStorageDirectory().getAbsolutePath() + "/Music/仙剑奇侠传六-主题曲-《誓言成晖》.mp3",
 Environment.getExternalStorageDirectory().getAbsolutePath() + "/Music/仙剑奇侠传六-主题曲-《剑客不能说》.mp3",
 Environment.getExternalStorageDirectory().getAbsolutePath() + "/Music/仙剑奇侠传六-主题曲-《镜中人》.mp3",
 Environment.getExternalStorageDirectory().getAbsolutePath() + "/Music/仙剑奇侠传六-主题曲-《浪花》.mp3"};
private int musicIndex = 1;

public static MediaPlayer mp = new MediaPlayer();
public MusicService() {
 try {
 musicIndex = 1;
 mp.setDataSource(musicDir[musicIndex]);
 mp.prepare();
 } catch (Exception e) {
 Log.d("hint","can't get to the song");
 e.printStackTrace();
 }
}

public void playOrPause() {
 if(mp.isPlaying()){
 mp.pause();
 } else {
 mp.start();
 }
}
public void stop() {
 if(mp != null) {
 mp.stop();
 try {
 mp.prepare();
 mp.seekTo(0);
 } catch (Exception e) {
 e.printStackTrace();
 }
 }
}
public void nextMusic() {
 if(mp != null && musicIndex < 3) {
 mp.stop();
 try {
 mp.reset();
 mp.setDataSource(musicDir[musicIndex+1]);
 musicIndex++;
 mp.prepare();
 mp.seekTo(0);
 mp.start();
 } catch (Exception e) {
 Log.d("hint", "can't jump next music");
 e.printStackTrace();
 }
 }
}
public void preMusic() {
 if(mp != null && musicIndex > 0) {
 mp.stop();
 try {
 mp.reset();
 mp.setDataSource(musicDir[musicIndex-1]);
 musicIndex--;
 mp.prepare();
 mp.seekTo(0);
 mp.start();
 } catch (Exception e) {
 Log.d("hint", "can't jump pre music");
 e.printStackTrace();
 }
 }
}

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

<service android:name="com.wsine.west.exp5_AfterClass.MusicService" android:exported="true"></service>

private ServiceConnection sc = new ServiceConnection() {
 @Override
 public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
 musicService = ((MusicService.MyBinder)iBinder).getService();
 }

 @Override
 public void onServiceDisconnected(ComponentName componentName) {
 musicService = null;
 }
};
private void bindServiceConnection() {
 Intent intent = new Intent(MainActivity.this, MusicService.class);
 startService(intent);
 bindService(intent, sc, this.BIND_AUTO_CREATE);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);

 Log.d("hint", "ready to new MusicService");
 musicService = new MusicService();
 Log.d("hint", "finish to new MusicService");
 bindServiceConnection();

 seekBar = (SeekBar)this.findViewById(R.id.MusicSeekBar);
 seekBar.setProgress(musicService.mp.getCurrentPosition());
 seekBar.setMax(musicService.mp.getDuration());

 musicStatus = (TextView)this.findViewById(R.id.MusicStatus);
 musicTime = (TextView)this.findViewById(R.id.MusicTime);

 btnPlayOrPause = (Button)this.findViewById(R.id.BtnPlayorPause);

 Log.d("hint", Environment.getExternalStorageDirectory().getAbsolutePath()+"/You.mp3");
}

public android.os.Handler handler = new android.os.Handler();
public Runnable runnable = new Runnable() {
 @Override
 public void run() {
 if(musicService.mp.isPlaying()) {
 musicStatus.setText(getResources().getString(R.string.playing));
 btnPlayOrPause.setText(getResources().getString(R.string.pause).toUpperCase());
 } else {
 musicStatus.setText(getResources().getString(R.string.pause));
 btnPlayOrPause.setText(getResources().getString(R.string.play).toUpperCase());
 }
 musicTime.setText(time.format(musicService.mp.getCurrentPosition()) + "/"
 + time.format(musicService.mp.getDuration()));
 seekBar.setProgress(musicService.mp.getCurrentPosition());
 seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
 @Override
 public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
 if (fromUser) {
  musicService.mp.seekTo(seekBar.getProgress());
 }
 }

 @Override
 public void onStartTrackingTouch(SeekBar seekBar) {

 }

 @Override
 public void onStopTrackingTouch(SeekBar seekBar) {

 }
 });
 handler.postDelayed(runnable, 100);
 }
};

@Override
protected void onResume() {
 if(musicService.mp.isPlaying()) {
 musicStatus.setText(getResources().getString(R.string.playing));
 } else {
 musicStatus.setText(getResources().getString(R.string.pause));
 }

 seekBar.setProgress(musicService.mp.getCurrentPosition());
 seekBar.setMax(musicService.mp.getDuration());
 handler.post(runnable);
 super.onResume();
 Log.d("hint", "handler post runnable");
}

public void onClick(View view) {
 switch (view.getId()) {
 case R.id.BtnPlayorPause:
 musicService.playOrPause();
 break;
 case R.id.BtnStop:
 musicService.stop();
 seekBar.setProgress(0);
 break;
 case R.id.BtnQuit:
 handler.removeCallbacks(runnable);
 unbindService(sc);
 try {
 System.exit(0);
 } catch (Exception e) {
 e.printStackTrace();
 }
 break;
 case R.id.btnPre:
 musicService.preMusic();
 break;
 case R.id.btnNext:
 musicService.nextMusic();
 break;
 default:
 break;
 }
}

@Override
public void onDestroy() {
 unbindService(sc);
 super.onDestroy();
}

<Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:id="@+id/BtnPlayorPause"
 android:text="@string/btnPlayorPause"
 android:onClick="onClick"/>