通过Activity 调用 Service 进行音乐播放，
使用 ServiceConnection 类进行Service 绑定，自定义MyMusicBinder 类继承Binder
在Service绑定成功后 将Service Binder保存在Activity中，
从而使Service与Activity进行通讯。

public class MyMusicBinder extends Binder {

    public boolean setMusic(int musicId) {
        Log.i("MyMusicBinder", "setMusic");
        //如果之前有先暂停
        stopMusic();

        try {
            player = MediaPlayer.create(getApplicationContext(), Config.musicIds[musicId]);
            nowId = musicId;
            player.start();
            Log.i("MyMusicBinder", "Music Start");
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }

    public String getNowMusicName() {
        if (nowId >= 0) {
            return Config.musicNames[nowId];
        } else {
            return "当前没有播放歌曲";
        }
    }

    public void stopMusic() {
        if (nowId >= 0) {
            if (player != null) {
                player.stop();
                Log.i("setMusic()", "停止当前播放音乐");
            }
            player = null;
        }
    }
}

@Nullable
@Override
public IBinder onBind(Intent intent) {
    Log.i("MyMusicService", "onBind");
    nowId = intent.getIntExtra("MusicId", -1);
    if (nowId != -1) {
        mBinder.setMusic(nowId);

    }
    return mBinder;
}

conn = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            Log.i("Main", "onServiceConnected");
            binder = (MusicService.MyMusicBinder) iBinder;
            getInfo();
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {
            Log.i("Main", "onServiceDisconnected");
            binder = null;
        }
    };
    music_lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
            Log.i("Main", "onItemClick " + l);
            startMusic((int)l);
        }
    });