Jamendo学习笔记之：播放流程

转自：http://mikewang.blog.51cto.com/3826268/890180

这一次主要是研究Jamendo的播放流程，相对比较繁复一些。播放显然要启动Service来实现，在这之前，Jamendo是怎么处理的。本文将简单展开。

(一) 基本流程图

(二) 实现

1. 启动

在Jamendo中，开发者习惯用被启动Activity的静态方法来完成这个功能。Gallery的Item点击事件之后，代码如下：

Album album = (Album) adapterView.getItemAtPosition(position);             PlayerActivity.launch(HomeActivity.this, album); 

2. 数据加载封装

这一部分的处理思路在笔记之七中已经详细的说明。只在此列出代码，如下：

public class PlayerAlbumLoadingDialog extends LoadingDialog<Album, Track[]>{          private Album mAlbum;      public PlayerAlbumLoadingDialog(Activity activity, int loadingMsg, int failMsg) {         super(activity, loadingMsg, failMsg);     }      @Override     public Track[] doInBackground(Album... params) {         mAlbum = params[0];                  JamendoGet2Api service = new JamendoGet2ApiImpl();         Track[] tracks = null;                  try {             tracks = service.getAlbumTracks(mAlbum, JamendoApplication.getInstance().getStreamEncoding());             Log.d("play_workflow", "doInBackground tracks is:" + tracks.toString());         } catch (JSONException e) {             e.printStackTrace();             return null;         } catch (WSError e) {             publishProgress(e);             cancel(true);         }         return tracks;              }       @Override     public void doStuffWithResult(Track[] tracks) {                  Intent intent = new Intent(mActivity, PlayerActivity.class);         Playlist playlist = new Playlist();         mAlbum.setTracks(tracks);         playlist.addTracks(mAlbum);                  intent.putExtra("playlist", playlist);         Log.d("play_workflow", "doStuffWithResult playlist is:" + playlist.toString());         mActivity.startActivity(intent);     }  } 

封装的示意图如下：

3. 播放列表加载及准备

数据封装完毕后，开始进行各种播放器的准备。我猜因为是开源软件的原因，部分代码写的不是很完善。比如if的某个条件，打了log之后，始终并未执行。我在代码中已经做了注释。handleIntent()方法里边处理已经封装好的PlayList类。代码如下：

private void handleIntent(){         Log.i(JamendoApplication.TAG, "PlayerActivity.handleIntent");          // This will be result of this intent handling         Playlist playlist = null;          Log.d("play_workflow", "data is:" + getIntent().getData());//本身并未给data赋值，所以执行的都是data==null的情形         // We need to handle Uri         if(getIntent().getData() != null){//不执行此条判断                          // Check if this intent was already once parsed              // we don't need to do that again             if(!getIntent().getBooleanExtra("handled", false)){                 Log.d("play_workflow", "handled is true" );                 mUriLoadingDialog = (LoadingDialog) new UriLoadingDialog(this, R.string.loading, R.string.loading_fail).execute();             }                          } else {             Log.d("play_workflow", "handled is false" );             playlist = (Playlist) getIntent().getSerializableExtra("playlist");             Log.d("play_workflow", "handle_intent playlist is:" + playlist);             loadPlaylist(playlist);         }     } 

其中loadPlaylist()方法的代码如下：

private void loadPlaylist(Playlist playlist){         Log.i(JamendoApplication.TAG, "PlayerActivity.loadPlaylist");         if(playlist == null)             return;                  mPlaylist = playlist;         if(mPlaylist != getPlayerEngine().getPlaylist()){//播放列表不相等，就要重新加载             //getPlayerEngine().stop();             getPlayerEngine().openPlaylist(mPlaylist);             getPlayerEngine().play();         }     } 

其实，jamendo的处理是使用了两步来实现的，示意图如下：

按照先后顺序，以openPlayList()为例，代码如下：

Step1：在handleIntent中执行

       代码如上所示

Step2：在IntentPlayEngine中

@Override         public void openPlaylist(Playlist playlist) {             mPlaylist = playlist;             if(mServicePlayerEngine != null){                 mServicePlayerEngine.openPlaylist(playlist);             }         } 

Step3：在PlayEngineImpl中

@Override     public void openPlaylist(Playlist playlist) {         if(!playlist.isEmpty())             mPlaylist = playlist;         else             mPlaylist = null;     } 

4. 启动服务播放

从3中， play方法最终调用到的也是PlayEngine中的。

这样，整个流程就ok了。但是整个流程下来，给人的感觉是，冗繁。

(三) 播放的控制

对于播放控制的处理是（以play键为例）：

1， 监听按键

代码如下：

/**      * on click play/pause and open playlist if necessary      */     private OnClickListener mPlayOnClickListener = new OnClickListener(){          @Override         public void onClick(View v) {             if(getPlayerEngine().isPlaying()){                 getPlayerEngine().pause();             } else {                 getPlayerEngine().play();             }         }      }; 

2， 调用接口，启动intent

代码如下：

@Override         public void play() {             if (mServicePlayerEngine != null) {                 Log.d("play_workflow", "mServicePlayerEngine is not null:" );                 playlistCheck();                 mServicePlayerEngine.play();             } else {                 Log.d("play_workflow", "mServicePlayerEngine is null");                 startAction(PlayerService.ACTION_PLAY);             }         } 

3， 执行Service指定操作

代码如下：

if(action.equals(ACTION_PLAY)){              mPlayerEngine.play();             return;         } 

最终执行的代码如下：

@Override     public void play() {                  if( mPlayerEngineListener.onTrackStart() == false ){             return; // apparently sth prevents us from playing tracks         }          // check if there is anything to play         if(mPlaylist != null){              // check if media player is initialized             if(mCurrentMediaPlayer == null){                 mCurrentMediaPlayer = build(mPlaylist.getSelectedTrack());             }              // check if current media player is set to our song             if(mCurrentMediaPlayer != null && mCurrentMediaPlayer.playlistEntry != mPlaylist.getSelectedTrack()){                 cleanUp(); // this will do the cleanup job                               mCurrentMediaPlayer = build(mPlaylist.getSelectedTrack());             }                          // check if there is any player instance, if not, abort further execution              if(mCurrentMediaPlayer == null)                 return;              // check if current media player is not still buffering             if(!mCurrentMediaPlayer.preparing){                  // prevent double-press                 if(!mCurrentMediaPlayer.isPlaying()){                     // i guess this mean we can play the song                     Log.i(JamendoApplication.TAG, "Player [playing] "+mCurrentMediaPlayer.playlistEntry.getTrack().getName());                                          // starting timer                     mHandler.removeCallbacks(mUpdateTimeTask);                     mHandler.postDelayed(mUpdateTimeTask, 1000);                                          mCurrentMediaPlayer.start();                 }             } else {                 // tell the mediaplayer to play the song as soon as it ends preparing                 mCurrentMediaPlayer.playAfterPrepare = true;             }         }     } 

(四) 思考

在播放准备及播放的流程上，有些冗余，代码不够清晰。我之前做过一个音乐播放器，采用的是bind service，回调让控制比较方便。Jamendo对于IntentPlayerEngine和PlayEngineImpl做出了相应的解释。未绑定的原因是适应代码的原始版本，减少重构量。

l IntentPlayerEngine

/**      * Since 0.9.8.7 we embrace "bindless" PlayerService thus this adapter. No      * big need of code refactoring, we just wrap sending intents around defined      * interface        *       * 意思是：因为jamendo使用的是无绑定的PlayService，所以有着这个适配器。不需要对代码      * 进行太多的重构。我们只需要通过这个指定的接口发送Intent就ok了。      * @author Lukasz Wisniewski      */     private class IntentPlayerEngine implements PlayerEngine  

l PlayEngineImpl

/**  * Player core engine allowing playback, in other words, a  * wrapper around Android's <code>MediaPlayer</code>, supporting  * <code>Playlist</code> classes  *   * @author Lukasz Wisniewski  */ public class PlayerEngineImpl implements PlayerEngine