public class MusicService extends Service {
    private String path = "mnt/sdcard/123.mp3";
    private MediaPlayer player;

    @Override
    public IBinder onBind(Intent intent) {
        //当执行完了onCreate后，就会执行onBind把操作歌曲的方法返回
        return new MyBinder();
    }

    @Override
    public void onCreate() {
        super.onCreate();
        //这里只执行一次，用于准备播放器
        player = new MediaPlayer();
        try {
            player.setDataSource(path);
            //准备资源
            player.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Log.e("服务", "准备播放音乐");
    }

    //该方法包含关于歌曲的操作
    public class MyBinder extends Binder {

        //判断是否处于播放状态
        public boolean isPlaying(){
            return player.isPlaying();
        }

        //播放或暂停歌曲
        public void play() {
            if (player.isPlaying()) {
                player.pause();
            } else {
                player.start();
            }
            Log.e("服务", "播放音乐");
        }

        //返回歌曲的长度，单位为毫秒
        public int getDuration(){
            return player.getDuration();
        }

        //返回歌曲目前的进度，单位为毫秒
        public int getCurrenPostion(){
            return player.getCurrentPosition();
        }

        //设置歌曲播放的进度，单位为毫秒
        public void seekTo(int mesc){
            player.seekTo(mesc);
        }
    }
}

    <Button
        android:id="@+id/play"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="play"
        android:text="播放" />

    <SeekBar
        android:id="@+id/sb"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

public class MainActivity extends AppCompatActivity {

    private MyConnection conn;
    private MusicService.MyBinder musicControl;

    private Button playBtn;
    private SeekBar seekBar;
    private static final int UPDATE_PROGRESS = 0;

    //使用handler定时更新进度条
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case UPDATE_PROGRESS:
                    updateProgress();
                    break;
            }
        }
    };

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

        playBtn = (Button) findViewById(R.id.play);
        seekBar = (SeekBar) findViewById(R.id.sb);

        Intent intent3 = new Intent(this, MusicService.class);
        conn = new MyConnection();
        //使用混合的方法开启服务，
        startService(intent3);
        bindService(intent3, conn, BIND_AUTO_CREATE);

        seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                //进度条改变
                if (fromUser){
                    musicControl.seekTo(progress);
                }
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {
                //开始触摸进度条
            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                //停止触摸进度条
            }
        });
    }

    private class MyConnection implements ServiceConnection {

        //服务启动完成后会进入到这个方法
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            //获得service中的MyBinder
            musicControl = (MusicService.MyBinder) service;
            //更新按钮的文字
            updatePlayText();
            //设置进度条的最大值
            seekBar.setMax(musicControl.getDuration());
            //设置进度条的进度
            seekBar.setProgress(musicControl.getCurrenPostion());
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        //进入到界面后开始更新进度条
        if (musicControl != null){
            handler.sendEmptyMessage(UPDATE_PROGRESS);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //退出应用后与service解除绑定
        unbindService(conn);
    }

    @Override
    protected void onStop() {
        super.onStop();
        //停止更新进度条的进度
        handler.removeCallbacksAndMessages(null);
    }

    //更新进度条
    private void updateProgress() {
        int currenPostion = musicControl.getCurrenPostion();
        seekBar.setProgress(currenPostion);
        //使用Handler每500毫秒更新一次进度条
        handler.sendEmptyMessageDelayed(UPDATE_PROGRESS, 500);
    }


    //更新按钮的文字
    public void updatePlayText() {
        if (musicControl.isPlaying()) {
            playBtn.setText("暂停");
            handler.sendEmptyMessage(UPDATE_PROGRESS);
        } else {
            playBtn.setText("播放");
        }
    }

    //调用MyBinder中的play()方法
    public void play(View view) {
        musicControl.play();
        updatePlayText();
    }
}