Android P 音乐播放中，插拔OTG U盘音乐会停止

音乐播放器的主要服务如下
packages/apps/SnapdragonMusic/src/com/android/music/MediaPlaybackService.java

其注册对外部存储的监控如下：

    /**
     * Registers an intent to listen for ACTION_MEDIA_EJECT notifications.
     * The intent will call closeExternalStorageFiles() if the external media
     * is going to be ejected, so applications can clean up any files they have open.
     */
    public void registerExternalStorageListener() {
        if (mUnmountReceiver == null) {
            mUnmountReceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();
                    if (action.equals(Intent.ACTION_MEDIA_EJECT)) {
                        if (mCurrentTrackInfo != null ) {
                            String curTrackPath = mCurrentTrackInfo.mData;
                            // if the currently playing track is on the SD card
                            if (curTrackPath != null && curTrackPath.contains(intent.getData().getPath())) {
                                saveQueue(true);
                                mQueueIsSaveable = false;
                                closeExternalStorageFiles(intent.getData().getPath());
                            }
                        }
                    } else if (action.equals(Intent.ACTION_MEDIA_MOUNTED)) {
                        // when play music in background, delete file in filemanager will not effect music to play
                        if (intent.getStringExtra("FileChange") != null) {
                            notifyChange(QUEUE_CHANGED);
                            notifyChange(META_CHANGED);
                            return;
                        }
                        mMediaMountedCount++;
                        mCardId = MusicUtils.getCardId(MediaPlaybackService.this);

                        // pause playback
                        pause();
                        reloadQueue();
                        mQueueIsSaveable = true;

                        notifyChange(PLAYSTATE_CHANGED);
                        notifyChange(QUEUE_CHANGED);
                        notifyChange(META_CHANGED);
                    } else if (action.equals(ACTION_DELETE_MUSIC)) {
                        long id = intent.getLongExtra("mid", -1);
                        long artindex = intent.getLongExtra("artindex", -1);
                        if (id != -1 && artindex != -1) {
                             MusicUtils.deleteTrack(MediaPlaybackService.this, id, artindex);
                        }
                    }
                }
            };
            IntentFilter iFilter = new IntentFilter();
            iFilter.addAction(Intent.ACTION_MEDIA_EJECT);
            iFilter.addAction(Intent.ACTION_MEDIA_MOUNTED);
            iFilter.addAction(ACTION_DELETE_MUSIC);
            iFilter.addDataScheme("file");
            registerReceiver(mUnmountReceiver, iFilter);
        }
    }

其中，挂载OTG U盘的监听事件是：Intent.ACTION_MEDIA_MOUNTED
从其实现的过程中可以找到：

// pause playback
                        pause();
                        reloadQueue();
                        mQueueIsSaveable = true;

                        notifyChange(PLAYSTATE_CHANGED);
                        notifyChange(QUEUE_CHANGED);
                        notifyChange(META_CHANGED);

pause即为将音乐停止的函数。其他的会对消息队列有更新处理.