Android开发中如何实现一个音乐播放器功能

/** 
* 用于从数据库中查询歌曲的信息，保存在List当中 
* 
* @return 
*/ 
public List getMp3Infos() { 
  Cursor cursor = getContentResolver().query( 
    MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, null, null, null, 
    MediaStore.Audio.Media.DEFAULT_SORT_ORDER); 
  List mp3Infos = new ArrayList(); 
  for (int i = 0; i < cursor.getCount(); i++) { 
    Mp3Info mp3Info = new Mp3Info(); 
    cursor.moveToNext(); 
    long id = cursor.getLong(cursor 
      .getColumnIndex(MediaStore.Audio.Media._ID));  //音乐id 
    String title = cursor.getString((cursor  
      .getColumnIndex(MediaStore.Audio.Media.TITLE)));//音乐标题 
    String artist = cursor.getString(cursor 
      .getColumnIndex(MediaStore.Audio.Media.ARTIST));//艺术家 
    long duration = cursor.getLong(cursor 
      .getColumnIndex(MediaStore.Audio.Media.DURATION));//时长 
    long size = cursor.getLong(cursor 
      .getColumnIndex(MediaStore.Audio.Media.SIZE)); //文件大小 
    String url = cursor.getString(cursor 
      .getColumnIndex(MediaStore.Audio.Media.DATA));       //文件路径 
  int isMusic = cursor.getInt(cursor 
    .getColumnIndex(MediaStore.Audio.Media.IS_MUSIC));//是否为音乐 
  if (isMusic != 0) {   //只把音乐添加到集合当中 
    mp3Info.setId(id); 
    mp3Info.setTitle(title); 
    mp3Info.setArtist(artist); 
    mp3Info.setDuration(duration); 
    mp3Info.setSize(size); 
    mp3Info.setUrl(url); 
    mp3Infos.add(mp3Info); 
    } 
  } 
return mp3Infos; 
} 

/** 
   * 填充列表 
   * @param mp3Infos 
   */ 
  public void setListAdpter(List mp3Infos) { 
    List> mp3list = new ArrayList>(); 
    for (Iterator iterator = mp3Infos.iterator(); iterator.hasNext();) { 
      Mp3Info mp3Info = (Mp3Info) iterator.next(); 
      HashMap map = new HashMap(); 
      map.put("title", mp3Info.getTitle()); 
      map.put("Artist", mp3Info.getArtist()); 
      map.put("duration", String.valueOf(mp3Info.getDuration())); 
      map.put("size", String.valueOf(mp3Info.getSize())); 
      map.put("url", mp3Info.getUrl()); 
      mp3list.add(map); 
    } 
    mAdapter = new SimpleAdapter(this, mp3list, 
        R.layout.music_list_item_layout, new String[] { "title", "Artist", "duration" }, 
        new int[] { R.id.music_title, R.id.music_Artist, R.id.music_duration }); 
    mMusiclist.setAdapter(mAdapter);   
  } 

mMusiclist = (ListView) findViewById(R.id.music_list); 
    mMusiclist.setOnItemClickListener(new MusicListItemClickListener()); 
    mp3Infos = getMp3Infos(); 
    setListAdpter(getMp3Infos()); 

private class MusicListItemClickListener implements OnItemClickListener { 
  @Override 
  public void onItemClick(AdapterView<?> parent, View view, int position, 
      long id) { 
    if(mp3Infos != null) { 
      Mp3Info mp3Info = mp3Infos.get(position); 
      Log.d("mp3Info-->", mp3Info.toString()); 
      Intent intent = new Intent(); 
      intent.putExtra("url", mp3Info.getUrl());     
      intent.putExtra("MSG", AppConstant.PlayerMsg.PLAY_MSG); 
      intent.setClass(MainActivity.this, PlayerService.class); 
      startService(intent);    //启动服务 
    } 
  } 
} 

package com.wwj.sb.service; 
 
 
import android.annotation.SuppressLint; 
import android.app.Service; 
import android.content.Intent; 
import android.media.MediaPlayer; 
import android.media.MediaPlayer.OnPreparedListener; 
import android.os.IBinder; 
 
import com.wwj.sb.domain.AppConstant; 
 
@SuppressLint("NewApi") 
public class PlayerService extends Service { 
  private MediaPlayer mediaPlayer = new MediaPlayer();    //媒体播放器对象 
  private String path;            //音乐文件路径 
  private boolean isPause;          //暂停状态 
   
  @Override 
  public IBinder onBind(Intent arg0) { 
    return null; 
  } 
   
  @Override 
  public int onStartCommand(Intent intent, int flags, int startId) { 
    if(mediaPlayer.isPlaying()) { 
      stop(); 
    } 
    path = intent.getStringExtra("url");     
    int msg = intent.getIntExtra("MSG", 0); 
    if(msg == AppConstant.PlayerMsg.PLAY_MSG) { 
      play(0); 
    } else if(msg == AppConstant.PlayerMsg.PAUSE_MSG) { 
      pause(); 
    } else if(msg == AppConstant.PlayerMsg.STOP_MSG) { 
      stop(); 
    } 
    return super.onStartCommand(intent, flags, startId); 
  } 
   
 
  /** 
   * 播放音乐 
   * @param position 
   */ 
  private void play(int position) { 
    try { 
      mediaPlayer.reset();//把各项参数恢复到初始状态 
      mediaPlayer.setDataSource(path); 
      mediaPlayer.prepare(); //进行缓冲 
      mediaPlayer.setOnPreparedListener(new PreparedListener(position));//注册一个监听器 
    } 
    catch (Exception e) { 
      e.printStackTrace(); 
    } 
  } 
   
  /** 
   * 暂停音乐 
   */ 
  private void pause() { 
    if (mediaPlayer != null && mediaPlayer.isPlaying()) { 
      mediaPlayer.pause(); 
      isPause = true; 
    } 
  } 
   
  /** 
   * 停止音乐 
   */ 
  private void stop(){ 
    if(mediaPlayer != null) { 
      mediaPlayer.stop(); 
      try { 
        mediaPlayer.prepare(); // 在调用stop后如果需要再次通过start进行播放,需要之前调用prepare函数 
      } catch (Exception e) { 
        e.printStackTrace(); 
      } 
    } 
  } 
   
   
  @Override 
  public void onDestroy() { 
    if(mediaPlayer != null){ 
      mediaPlayer.stop(); 
      mediaPlayer.release(); 
    } 
  } 
  /** 
   * 
   * 实现一个OnPrepareLister接口,当音乐准备好的时候开始播放 
   * 
   */ 
  private final class PreparedListener implements OnPreparedListener { 
    private int positon; 
     
    public PreparedListener(int positon) { 
      this.positon = positon; 
    } 
     
    @Override 
    public void onPrepared(MediaPlayer mp) { 
      mediaPlayer.start();  //开始播放 
      if(positon > 0) {  //如果音乐不是从头播放 
        mediaPlayer.seekTo(positon); 
      } 
    } 
  } 
   
}