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