Android之MediaPlayer一个bug

本文主要记录使用Android 的MediaPlayer时遇见的一个很奇怪的bug

播放音乐时会出现调用了start,但是没有声音出来
* 测试机器：华为Honor 8, Android 7.0;
* 需求：在音乐列表界面播放音乐，音乐分为本地音乐和网络音乐
* 工具：IjkMediaPlayer在播放网络音乐时差不多有个10秒的延时，就是用户点击到播放出来差不多要10秒（网没有问题，很快），播放本地音乐没有这个问题，暂时无解，所以使用Android 提供的MediaPlayer.
* 思路：按照我的理解嘛，把网络和本地的音乐播放代码用一个，所以使用异步prepare,(注意，这里埋下了问题)，因为是在列表里，音乐有很多，点击音乐A播放，再次点击A是暂停，然后再次点击A是继续播放，很简单的功能，所以加了一个判断，记录了上一次的播放的音乐地址，如果不一样，就需要重新初始化Mediaplayer, 因为要联网获取，懒得开线程，直接使用MediaPlayer的异步操作prepareAsync()，写如下出来的代码

```@Overridepublic void play(@NonNull String url) {    play(url, false);}@Overridepublic void play(@NonNull String url, boolean restart) {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer == null) {                mMediaPlayer = new MediaPlayer();            }            if (restart || !mLastPlayMusicUrl.equals(url)) {                mMediaPlayer.reset();                mMediaPlayer.setLooping(true);                mMediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);                mMediaPlayer.setOnPreparedListener(mMediaPrepareListener);                mMediaPlayer.setVolume(0.5f, 0.5f);                mMediaPlayer.setDataSource(url);                mLastPlayMusicUrl = url;                mMusicIsPlaying = true;                mMediaPlayer.prepareAsync();            } else {                mMediaPlayer.start();            }        } catch (Exception e) {            e.printStackTrace();            D.e("play music error : " + e.getMessage() + " path:" + url + " file exists:" + new File(url).exists());        }    }}private MediaPlayer.OnPreparedListener        mMediaPrepareListener = new MediaPlayer.OnPreparedListener() {    @Override    public void onPrepared(MediaPlayer mp) {        synchronized (mPlayerLocker) {            if (mMediaPlayer != null) {                if (mMusicIsPlaying) {                    mMediaPlayer.start();                }                else {                    mMediaPlayer.pause();                }            }        }    }};```

* 正常使用，上面的代码是没有问题，但是我们的操作可能比较不正常吧，注意上面的代码play(@NonNull String url, boolean restart)，第二个参数如果是true,会重新初始化播放器，对同一首音乐，播放，暂停，播放，暂停，播放(重新初始化), 暂停，播放(重新初始化), 暂停，播放(重新初始化), 暂停，播放(重新初始化)…,差不多重复10次左右吧，会出现一次播放时没有声音，但是暂停后，再播放，就又正常了，代码确实去调用了，prepare()了，也start()了。
* 很郁闷，找不到问题，然后大胆猜测是不是异步播放导致的，代码暂时换成同步的，只测试本地的音乐，测试50次，没有复现，尝试了很多其他办法，发现同步是比较好的一种方式
* 解决方案：本地的用同步的方式，网络的用异步的方式，附上测试播放的代码

```public class SlackMusicPlayer {public final static SlackMusicPlayer instance = new SlackMusicPlayer();private Thread mPrepareThread = null;private SlackMusicPlayer() {    //}private MediaPlayer mMediaPlayer;private String mLastPlayMusicUrl = "";private boolean mMusicIsPlaying = false;private final Object mPlayerLocker = new Object();@Overridepublic void play(@NonNull String url) {    play(url, false);}@Overridepublic void play(@NonNull String url, boolean restart) {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer == null) {                mMediaPlayer = new MediaPlayer();            }            if (restart || !mLastPlayMusicUrl.equals(url)) {                mMediaPlayer.reset();                mMediaPlayer.setLooping(true);                mMediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);                mMediaPlayer.setVolume(0.5f, 0.5f);                mMediaPlayer.setDataSource(url);                mLastPlayMusicUrl = url;                mMusicIsPlaying = true;                if (mPrepareThread != null) {                    mPrepareThread.interrupt();                }                mPrepareThread = null;                if (url.startsWith("/")) {// 本地音乐文件                    mMediaPlayer.setOnPreparedListener(null);                    mPrepareThread = new Thread(new Runnable() {                        @Override                        public void run() {                            try {                                synchronized (mPlayerLocker) {                                    if (mMediaPlayer != null && mMusicIsPlaying) {                                        mMediaPlayer.prepare();                                        mMediaPlayer.start();                                    }                                }                            } catch (Exception e) {                                e.printStackTrace();                            }                        }                    });                    mPrepareThread.start();                } else {                    mMediaPlayer.setOnPreparedListener(mMediaPrepareListener);                    mMediaPlayer.prepareAsync();                }            } else {                mMediaPlayer.start();            }        } catch (Exception e) {            e.printStackTrace();            D.e("play music error : " + e.getMessage() + " path:" + url + " file exists:" + new File(url).exists());        }    }}@Overridepublic void setVolume(float left, float right) {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer != null) {                mMediaPlayer.setVolume(left, right);            }        }        catch (Exception e) {            e.printStackTrace();        }    }}@Overridepublic void pause() {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer != null) {                mMediaPlayer.pause();            }        }        catch (Exception e) {            e.printStackTrace();        }        mMusicIsPlaying = false;    }}@Overridepublic void reset() {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer != null) {                mMediaPlayer.reset();            }        }        catch (Exception e) {            e.printStackTrace();        }        mMusicIsPlaying = false;        mLastPlayMusicUrl = "";    }}@Overridepublic void release() {    synchronized (mPlayerLocker) {        try {            if (mMediaPlayer != null) {                mMediaPlayer.release();            }        }        catch (Exception e) {            e.printStackTrace();        }        mMusicIsPlaying = false;        mMediaPlayer = null;    }}private MediaPlayer.OnPreparedListener        mMediaPrepareListener = new MediaPlayer.OnPreparedListener() {    @Override    public void onPrepared(MediaPlayer mp) {        synchronized (mPlayerLocker) {            if (mMediaPlayer != null) {                if (mMusicIsPlaying) {                    mMediaPlayer.start();                }                else {                    mMediaPlayer.pause();                }            }        }    }};

}

```