BroadcastReceiver的实例----基于Service的音乐播放器之二

Posted 奋斗青年一族

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该程序的后台Service会在播放状态发生改变时对外发送广播(广播将会激发前台Activity的BroadcastReceiver);它也会采用BroadcastReceiver监听来自前台Activity所发出的广播。后台Service的代码如下:

import java.io.IOException;

import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.AssetFileDescriptor;
import android.content.res.AssetManager;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.IBinder;

public class MusicService extends Service{
  MyReceiver serviceReceiver;
  AssetManager am;
  String[] musics = new String[]{
      "wish.mp3","promise.mp3","beautiful.mp3"
  };
  MediaPlayer mPlayer;
  //当前的状态,0x11代表没有播放,0x12代表正在播放,0x13代表暂停
  int status = 0x11;
  //记录当前正在播放的音乐
  int current = 0;

  @Override
  public IBinder onBind(Intent intent) {
    return null;
  }
  @Override
  public void onCreate() {
    am = getAssets();
    //创建BroadcastReceiver
    serviceReceiver = new MyReceiver();
    //创建IntentFilter
    IntentFilter filter = new IntentFilter();
    filter.addAction(MusicBox.CTL_ACTION);
    registerReceiver(serviceReceiver, filter);
    //创建MediaPlayer
    mPlayer = new MediaPlayer();
    //为MediaPlayer播放完成事件绑定监听器
    mPlayer.setOnCompletionListener(new 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(MusicBox.UPDATE_ACTION);
        sendIntent.putExtra("current", current);
        //发送广播,将被Activity组件中的BroadcastReceiver接收到
        sendBroadcast(sendIntent);
        //准备并播放音乐
        prepareAndPlay(musics[current]);
      }
    });
    super.onCreate();
  }

  public class MyReceiver extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
      int control = intent.getIntExtra("control", -1);

      switch(control){
        //播放或暂停
        case 1:
          //原来处于没有播放状态
          if(status == 0x11){
            //准备并播放音乐
            prepareAndPlay(musics[current]);
            status = 0x12;
          }
          //原来处于播放状态
          else if(status == 0x12){
            //暂停
            mPlayer.pause();
            //改变为暂停状态
            status = 0x13;
          }
          //原来处于暂停状态
          else if(status == 0x13){
            //播放
            mPlayer.start();
            //改变状态
            status = 0x12;
          }
          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
          mPlayer.stop();
          status = 0x11;

        }
      }
      //发送广播通知Activity更改图标、文本框
      Intent sendIntent = new Intent(MusicBox.UPDATE_ACTION);
      sendIntent.putExtra("update", status);
      sendIntent.putExtra("current", current);
      //发送广播,将被Activity组件中的BroadcastReceiver接收到
      sendBroadcast(sendIntent);

    }
  }  
  private void prepareAndPlay(String music){
    try {
      //打开指定音乐文件
      AssetFileDescriptor afd = am.openFd(music);
      mPlayer.reset();
      //使用MediaPlayer加载指定的声音文件
      mPlayer.setDataSource(afd.getFileDescriptor(),
      afd.getStartOffset(),afd.getLength());
      //准备声音
      mPlayer.prepare();
      //播放
      mPlayer.start();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

}

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