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;
    }
}