ServiceThe background service controls the pause and stop of music playback, and automatically plays the next song after playing.

    //Add the permission to obtain the status of the sd card and the permission to read the sd card < uses - 
    permission android:name= "android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> 
    < uses - 
    permission android:name= "android.permission.READ_EXTERNAL_STORAGE" / >
 // MainActivity uses three buttons, play, pause, stop, and sends services to background services to control
 public class MainActivity extends Activity implements OnClickListener {
         private Button puase ;
         private Button stop ;
         private Button start ;
 @Override

        
                protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            start = (Button) findViewById(R.id.start);
            puase = (Button) findViewById(R.id.puase);
            stop = (Button) findViewById(R.id.stop);

            start.setOnClickListener(this);
            puase.setOnClickListener(this);
            stop.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, Service1.class);
            switch (v.getId()) {
                case R.id.start:
                    intent.putExtra("key", 1);
                    break;
                case R.id.puase:
                    intent.putExtra("key", 2);
                    break;
                case R.id.stop:
                    intent.putExtra("key", 3);
                    break;
                default:
                    break;
            }
            startService(intent);
        }
    }
    //自定义类,继承Service服务
    public class Service1 extends Service {
        private MediaPlayer mediaplayer;
        private ArrayList<Music> list;
        private String path = "";
        private int index = 0;

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

        @Override
        public void onCreate() {
            super.onCreate();
            mediaplayer = new MediaPlayer();
            list = new ArrayList<Music>();
            //读取SD卡
            if (Environment.getExternalStorageState().equals(
                    Environment.MEDIA_MOUNTED)) {
                File file = Environment.getExternalStorageDirectory();
                path = file.getAbsolutePath();
            }
            list.add(new Music("男人歌", path + "/nanrenge.mp3"));
            list.add(new Music("夜色", path + "/yese.mp3"));
            list.add(new Music("漂洋过海来看你", path + "/piaoyang.mp3"));
            list.add(new Music("兄弟无数", path + "/xiongdiwushu.mp3"));
            //播放完成后自定播放下一曲
            mediaplayer.setOnCompletionListener(new OnCompletionListener() {

                @Override
                public void onCompletion(MediaPlayer mp) {
                    index++;
                    play();
                }
            });
        }
	//用这个方法控制MainActivity发来的服务,控制音乐
        @Override
        public int onStartCommand(Intent intent, int flags, int startId) {
            int m = intent.getIntExtra("key", 0);
            switch (m) {
                case 1:
                    play();
                    break;
                case 2:// 暂停
                    if (mediaplayer != null && mediaplayer.isPlaying())
                        mediaplayer.pause();
                    break;
                case 3:// 停止
                    if (mediaplayer != null) {
                        mediaplayer.stop();
                        stopService(intent);
                    }
                    break;

                default:
                    break;
            }
            return super.onStartCommand(intent, flags, startId);
        }
	//播放音乐
        private void play() {
            mediaplayer.reset();
            try {
                mediaplayer.setDataSource(list.get(index).getPath());
                mediaplayer.prepare();
            } catch (Exception e) {
                e.printStackTrace();
            }
            mediaplayer.start();
        }

        @Override
        public void onDestroy() {
            super.onDestroy();
            if (mediaplayer != null) {
                mediaplayer.release();
                mediaplayer = null;
            }
        }

    }