Android基于Service的音乐播放器

2019-12-12 05:47:11

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本文开发一个基于Service的音乐播放器，音乐由后台运行的Service负责播放，当后台的播放状态发生变化时，程序将会通过发送广播通知前台Activity更新界面；当点击Activity的界面按钮时，系统将通过发送广播通知后台Service来改变播放状态。

前台Activity界面有两个按钮，分别用于控制播放/暂停、停止，另外还有两个文本框，用于显示正在播放的歌曲名、歌手名。前台Activity的代码如下：

public class MainActivity extends AppCompatActivity implements View.OnClickListener{  private ImageButton mStart;  private ImageButton mStop;  private TextView mMusicName;  private TextView mSongerName;  private ActivityReceiver mActivityReceiver;  public static final String CTL_ACTION = "com.trampcr.action.CTL_ACTION";  public static final String UPDATE_ACTION = "com.trampcr.action.UPDATE_ACTION";  //定义音乐播放状态，0x11代表没有播放，0x12代表正在播放，0x13代表暂停  int status = 0x11;  String[] musicNames = new String[]{"完美生活", "那一年", "故乡"};  String[] songerNames = new String[]{"许巍", "许巍", "许巍"};  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    mStart = (ImageButton) findViewById(R.id.start);    mStop = (ImageButton) findViewById(R.id.stop);    mMusicName = (TextView) findViewById(R.id.music_name);    mSongerName = (TextView) findViewById(R.id.songer_name);    mStart.setOnClickListener(this);    mStop.setOnClickListener(this);    mActivityReceiver = new ActivityReceiver();    //创建IntentFilter    IntentFilter filter = new IntentFilter();    //指定BroadcastReceiver监听的Action    filter.addAction(UPDATE_ACTION);    //注册BroadcastReceiver    registerReceiver(mActivityReceiver, filter);    Intent intent = new Intent(MainActivity.this, MusicService.class);    //启动后台Service    startService(intent);  }  public class ActivityReceiver extends BroadcastReceiver {    @Override    public void onReceive(Context context, Intent intent) {      //获取Intent中的update消息，update代表播放状态      int update = intent.getIntExtra("update", -1);      //获取Intent中的current消息，current代表当前正在播放的歌曲      int current = intent.getIntExtra("current", -1);      if (current >= 0){        mMusicName.setText(musicNames[current]);        mSongerName.setText(songerNames[current]);      }      switch (update){        case 0x11:          mStart.setBackgroundResource(R.drawable.play);          status = 0x11;          break;        //控制系统进入播放状态        case 0x12:          //在播放状态下设置使用暂停图标          mStart.setBackgroundResource(R.drawable.pause);          status = 0x12;          break;        case 0x13:          //在暂停状态下设置使用播放图标          mStart.setBackgroundResource(R.drawable.play);          status = 0x13;          break;      }    }  }  @Override  public void onClick(View v) {    Intent intent = new Intent(CTL_ACTION);    switch (v.getId()){      case R.id.start:        intent.putExtra("control", 1);        break;      case R.id.stop:        intent.putExtra("control", 2);        break;    }    //发送广播，将被Service中的BroadcastReceiver接收到    sendBroadcast(intent);  }}

ActivityReceiver()用于响应后台Service所发出的广播，该程序将会根据广播Intent里的消息来改变播放状态，并更新程序界面中按钮的图标。

onClick中根据点击的按钮发送广播，发送广播时会把所按下的按钮标识发送出来。

接下来是后台Service，会在播放状态发生改变时对外发送广播。代码如下：

public class MusicService extends Service {  MyReceiver serviceReceiver;  AssetManager mAssetManager;  String[] musics = new String[]{"prefectLife.mp3", "thatYear.mp3", "country.mp3"};  MediaPlayer mMediaPlayer;  int status = 0x11;  int current = 0; // 记录当前正在播放的音乐  @Nullable  @Override  public IBinder onBind(Intent intent) {    return null;  }  @Override  public void onCreate() {    super.onCreate();    mAssetManager = getAssets();    serviceReceiver = new MyReceiver();    //创建IntentFilter    IntentFilter filter = new IntentFilter();    filter.addAction(MainActivity.CTL_ACTION);    registerReceiver(serviceReceiver, filter);    //创建MediaPlayer    mMediaPlayer = new MediaPlayer();    //为MediaPlayer播放完成事件绑定监听器    mMediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {      @Override      public void onCompletion(MediaPlayer mp) {        current++;        if (current >= 3) {          current = 0;        }        //发送广播通知Activity更改文本框        Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);        sendIntent.putExtra("current", current);        //发送广播，将被Activity中的BroadcastReceiver接收到        sendBroadcast(sendIntent);        //准备并播放音乐        prepareAndPlay(musics[current]);      }    });  }  public class MyReceiver extends BroadcastReceiver {    @Override    public void onReceive(Context context, Intent intent) {      int control = intent.getIntExtra("control", -1);      switch (control){        case 1: // 播放或暂停          //原来处于没有播放状态          if (status ==0x11){            //准备播放音乐            prepareAndPlay(musics[current]);            status = 0x12;          }          //原来处于播放状态          else if (status == 0x12){            //暂停            mMediaPlayer.pause();            status = 0x13; // 改变为暂停状态          }          //原来处于暂停状态          else if (status == 0x13){            //播放            mMediaPlayer.start();            status = 0x12; // 改变状态          }          break;        //停止声音        case 2:          //如果原来正在播放或暂停          if (status == 0x12 || status == 0x13){            //停止播放            mMediaPlayer.stop();            status = 0x11;          }      }      //广播通知Activity更改图标、文本框      Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);      sendIntent.putExtra("update", status);      sendIntent.putExtra("current", current);      //发送广播，将被Activity中的BroadcastReceiver接收到      sendBroadcast(sendIntent);    }  }  private void prepareAndPlay(String music) {    try {      //打开指定的音乐文件      AssetFileDescriptor assetFileDescriptor = mAssetManager.openFd(music);      mMediaPlayer.reset();      //使用MediaPlayer加载指定的声音文件      mMediaPlayer.setDataSource(assetFileDescriptor.getFileDescriptor(), assetFileDescriptor.getStartOffset(), assetFileDescriptor.getLength());      mMediaPlayer.prepare(); // 准备声音      mMediaPlayer.start(); // 播放    } catch (IOException e) {      e.printStackTrace();    }  }}

MyReceiver用于接收前台Activity所发出的广播，并根据广播的消息内容改变Service的播放状态，当播放状态改变时，该Service对外发送一条广播，广播消息将会被前台Activity接收，前台Activity将会根据广播消息更新界面。

为了让该音乐播放器能按顺序依次播放歌曲，程序为MediaPlayer增加了OnCompletionListener监听器，当MediaPlayer播放完成后将自动播放下一首歌曲。

运行程序，效果图如下：