Jamendo学习笔记之八：播放流程

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{

    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 MediaPlayer, supporting
 * Playlist classes
 *
 * @author Lukasz Wisniewski
 */
public class PlayerEngineImpl implements PlayerEngine