ANDROID_MARS学习笔记_S01原始版_023_MP3PLAYER005_用广播BroacastReciever实现后台播放不更新歌词

一、代码流程
1.自定义一个AppConstant.LRC_MESSAGE_ACTION字符串表示广播"更新歌词"

2.在PlayerActivity的onResume()注册BroadcastReceiver，在onPause解除BroadcastReceiver

3.自定义LrcMessageBroadcastReceiver继承BroadcastReceiver,在onCreate()通过intent获取歌词，更新UI

4.所有更新歌词的操作移到PlayerService中
二、代码
1.xml

2.java
(1)PlayerActivity.java

 package tony.mp3player;

 import tony.model.Mp3Info;
 import tony.mp3player.service.PlayerService;
 import android.app.Activity;
 import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.ImageButton;
 import android.widget.TextView;

 //更新歌词的工作不再在activity中完成，Activity只被动地接收service的广播以更新歌词，
 //原来的相关歌词操作挪到service中完成
 public class PlayerActivity extends Activity {

     private ImageButton beginBtn = null;
     private ImageButton pauseBtn = null;
     private ImageButton stopBtn = null;

     private TextView lrcTextView = null;
     private Mp3Info info = null;

     private IntentFilter intentFilter = null;
     private BroadcastReceiver receiver = null;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.player);
         Intent intent = getIntent();
         info = (Mp3Info) intent.getSerializableExtra("mp3Info");
         beginBtn = (ImageButton) findViewById(R.id.begin);
         pauseBtn = (ImageButton) findViewById(R.id.pause);
         stopBtn = (ImageButton) findViewById(R.id.stop);
         lrcTextView = (TextView) findViewById(R.id.lrcText);

         beginBtn.setOnClickListener(new BeginListener());
         pauseBtn.setOnClickListener(new PauseListener());
         stopBtn.setOnClickListener(new StopListener());
     }

     @Override
     protected void onPause() {
         super.onPause();
         unregisterReceiver(receiver);
     }

     @Override
     protected void onResume() {
         super.onResume();
         receiver = new LrcMessageBroadcastReceiver();
         registerReceiver(receiver, getIntentFilter());
     }

     private IntentFilter getIntentFilter() {
         if(intentFilter == null) {
             intentFilter = new IntentFilter();
             intentFilter.addAction(AppConstant.LRC_MESSAGE_ACTION);
         }
         return intentFilter;
     }

     /**
      * 广播接收器，主要接收service放送的广播，并且更新UI，也就是放置歌词 的textview
      * @author T
      *
      */
     class LrcMessageBroadcastReceiver extends BroadcastReceiver {
         public void onReceive(Context context, Intent intent) {
             String lrcMessage = intent.getStringExtra("lrcMessage");
             lrcTextView.setText(lrcMessage);
         }
     }

     class BeginListener implements OnClickListener {
         @Override
         public void onClick(View v) {
             Intent intent = new Intent();
             intent.putExtra("mp3Info", info);
             intent.putExtra("MSG", AppConstant.PlayerMsg.PLAY_MSG);
             intent.setClass(PlayerActivity2.this, PlayerService.class);
             startService(intent);
         }
     }

     class PauseListener implements OnClickListener {
         @Override
         public void onClick(View v) {
             //通知Service暂停播放MP3
             Intent intent = new Intent();
             intent.putExtra("MSG", AppConstant.PlayerMsg.PAUSE_MSG);
             intent.setClass(PlayerActivity2.this, PlayerService.class);
             startService(intent);
         }
     }

     class StopListener implements OnClickListener {
         @Override
         public void onClick(View v) {
             //通知Service停止播放MP3文件
             Intent intent = new Intent();
             intent.putExtra("MSG", AppConstant.PlayerMsg.STOP_MSG);
             intent.setClass(PlayerActivity2.this, PlayerService.class);
             startService(intent);
         }
     }
 }

(2)PlayerService.java

 package tony.mp3player.service;

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.InputStream;
 import java.util.List;
 import java.util.Queue;

 import tony.model.Mp3Info;
 import tony.mp3player.AppConstant;
 import tony.mp3player.LrcProcessor;
 import android.app.Service;
 import android.content.Intent;
 import android.media.MediaPlayer;
 import android.net.Uri;
 import android.os.Environment;
 import android.os.Handler;
 import android.os.IBinder;

 public class PlayerService extends Service {

     private boolean isPlaying = false;
     private boolean isPause = false;
     private boolean isReleased = false;
     private MediaPlayer mediaPlayer = null;

     private Mp3Info info = null;
     private List<Queue> queues = null;
     private Handler handler = new Handler();
     private UpdateTimeCallback updateTimeCallback = null;
     private long begin = 0;
     private long nextTimeMill = 0;
     private long currentTimeMill = 0;
     private String msg = null;
     private long pauseTimeMills = 0;

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

     @Override
     public int onStartCommand(Intent intent, int flags, int startId) {
         info = (Mp3Info) intent.getSerializableExtra("mp3Info");
         int MSG = intent.getIntExtra("MSG", 0);
         if(info != null) {
             if(MSG == AppConstant.PlayerMsg.PLAY_MSG) {
                 play(info);
             }
         } else {
             if(MSG == AppConstant.PlayerMsg.PAUSE_MSG) {
                 pause();
             }
             else if(MSG == AppConstant.PlayerMsg.STOP_MSG) {
                 stop();
             }
         }
         return super.onStartCommand(intent, flags, startId);
     }

     /**
      * 根据歌词文件的名字，来读取歌词文件当中的信息
      * @param lrcName
      */
     private void prepareLrc(String lrcName) {
         try {
             InputStream inputStream;
             inputStream = new FileInputStream(Environment.getExternalStorageDirectory().getAbsolutePath() +
                     File.separator + "mp3" + File.separator + info.getLrcName());
             LrcProcessor lrcProcessor = new LrcProcessor();
             queues = lrcProcessor.process(inputStream);
             updateTimeCallback = new UpdateTimeCallback(queues);
             begin = 0;
             currentTimeMill = 0;
             nextTimeMill = 0;
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

     class UpdateTimeCallback implements Runnable{
         Queue<Long> times = null;
         Queue<String> msgs = null;

         public UpdateTimeCallback(List<Queue> queues) {
             this.times = queues.get(0);
             this.msgs = queues.get(1);
         }

         @Override
         public void run() {
             //计算偏移量，也就是说从开始播放MP3到现在为止，共消耗了多少时间，以毫秒为单位
             long offset = System.currentTimeMillis() - begin;
             if(currentTimeMill == 0) {//刚开始播放时，调用prepareLrc()，在其中设置currentTimeMill=0
                 nextTimeMill = times.poll();
                 msg = msgs.poll();
             }
             //歌词的显示是如下：例如
             //[00:01.00]Look
             //[00:03.00]Up
             //[00:06.00]Down
             //则在第1~3秒间是显示“look”,在第3~6秒间是显示"Up",在第6秒到下一个时间点显示"Down"
             if(offset >= nextTimeMill) {
                 //发送广播，把此刻应该显示的歌词传出去
                 Intent intent = new Intent();
                 intent.setAction(AppConstant.LRC_MESSAGE_ACTION);
                 intent.putExtra("lrcMessage", msg);
                 sendBroadcast(intent);
                 msg = msgs.poll();
                 nextTimeMill = times.poll();
             }
             currentTimeMill = currentTimeMill + 100;
             //在run方法里调用postDelayed，则会形成循环，每0.01秒执行一次线程
             handler.postDelayed(updateTimeCallback, 100);
         }
     }

     private void play(Mp3Info info) {
         if(!isPlaying) {
             String path = getMp3Path(info);
             mediaPlayer = MediaPlayer.create(this, Uri.parse("file://" + path));
             mediaPlayer.setLooping(false);
             mediaPlayer.start();
             isPlaying = true;
             isReleased = false;

             prepareLrc(info.getLrcName());
             handler.postDelayed(updateTimeCallback, 5);
             begin = System.currentTimeMillis();
         }
     }

     private void pause() {
         if(mediaPlayer != null) {
             if(!isReleased){
                 if(!isPause) {
                     mediaPlayer.pause();
                     //不再更新歌词
                     handler.removeCallbacks(updateTimeCallback);
                     //用来下面代码计算暂停了多久
                     pauseTimeMills = System.currentTimeMillis();
                 } else {
                     mediaPlayer.start();
                     handler.postDelayed(updateTimeCallback, 5);
                     //因为下面的时间偏移是这样计算的offset = System.currentTimeMillis() - begin;
                     //所以要把暂停的时间加到begin里去,
                     begin = System.currentTimeMillis() - pauseTimeMills + begin;
                 }
                 isPause = !isPause;
                 isPlaying = !isPlaying;
             }
         }
     }

     private void stop() {
         if(mediaPlayer != null) {
             if(isPlaying) {
                 if(!isReleased) {
                     //从Handler当中移除updateTimeCallback
                     handler.removeCallbacks(updateTimeCallback);
                     mediaPlayer.stop();
                     mediaPlayer.release();
                     isReleased = true;
                     isPlaying = false;
                 }
             }
         }
     }

     private String getMp3Path(Mp3Info mp3Info) {
         String SDCardRoot = Environment.getExternalStorageDirectory()
                 .getAbsolutePath();
         String path = SDCardRoot + File.separator + "mp3" + File.separator
                 + mp3Info.getMp3Name();
         return path;
     }
 }