媒体会话兼容未在 Pre-Lollipop 上显示锁屏控件

我在用着MediaSessionCompat来自 AppCompat 支持库修订版 22。在 Lollipop 上，我收到通知，而且锁屏的背景是专辑封面。一切都很顺利。

在棒棒糖之前的设备上，锁屏上的音乐控件根本不显示。这很奇怪，我尝试了一切，但它没有出现，甚至背景也没有改变。

我希望有人能解决这个问题。

Note: RemoteControlClient曾参与 Lollipop 和 KitKat 的工作

/**
 * Initializes the remote control client
 */
private void setupMediaSession() {
    /* Activate Audio Manager */
    mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
    mAudioManager.requestAudioFocus(mAudioFocusListener, AudioManager.STREAM_MUSIC,
            AudioManager.AUDIOFOCUS_GAIN);

    ComponentName mRemoteControlResponder = new ComponentName(getPackageName(),
            MediaButtonReceiver.class.getName());
    final Intent mediaButtonIntent = new Intent(Intent.ACTION_MEDIA_BUTTON);
    mediaButtonIntent.setComponent(mRemoteControlResponder);
    mMediaSessionCompat = new MediaSessionCompat(getApplication(), "JairSession", mRemoteControlResponder, null);
    mMediaSessionCompat.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS | MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS);
    PlaybackStateCompat playbackStateCompat = new PlaybackStateCompat.Builder()
            .setActions(
                    PlaybackStateCompat.ACTION_SEEK_TO |
                    PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS |
                    PlaybackStateCompat.ACTION_SKIP_TO_NEXT |
                    PlaybackStateCompat.ACTION_PLAY |
                    PlaybackStateCompat.ACTION_PAUSE |
                    PlaybackStateCompat.ACTION_STOP
            )
            .setState(
                    isPlaying() ? PlaybackStateCompat.STATE_PLAYING : PlaybackStateCompat.STATE_PAUSED,
                    getCurrentPosition(),
                    1.0f)
            .build();
    mMediaSessionCompat.setPlaybackState(playbackStateCompat);
    mMediaSessionCompat.setCallback(mMediaSessionCallback);
    mMediaSessionCompat.setSessionActivity(retrievePlaybackActions(5));
    mMediaSessionCompat.setActive(true);
    updateMediaSessionMetaData();
    mTransportController = mMediaSessionCompat.getController().getTransportControls();

这是updateMediaSessionMetaData() :

/**
 * Updates the lockscreen controls, if enabled.
 */
private void updateMediaSessionMetaData() {
            MediaMetadataCompat.Builder builder = new MediaMetadataCompat.Builder();
            builder.putString(MediaMetadataCompat.METADATA_KEY_ARTIST, getArtistName());
            builder.putString(MediaMetadataCompat.METADATA_KEY_ALBUM, getAlbumName());
            builder.putString(MediaMetadataCompat.METADATA_KEY_TITLE, getTrackName());
            builder.putLong(MediaMetadataCompat.METADATA_KEY_DURATION, getDuration());
            builder.putBitmap(MediaMetadataCompat.METADATA_KEY_ALBUM_ART, MusicUtils.getArtwork(this, getAlbumID(), true));
            mMediaSessionCompat.setMetadata(builder.build());

}

媒体会话回调方法

private final MediaSessionCompat.Callback mMediaSessionCallback = new MediaSessionCompat.Callback() {

    @Override
    public boolean onMediaButtonEvent(Intent mediaButtonEvent) {
        final String intentAction = mediaButtonEvent.getAction();
        if (AudioManager.ACTION_AUDIO_BECOMING_NOISY.equals(intentAction)) {
            if (PrefUtils.isHeadsetPause(getBaseContext())) {
                Log.d(LOG_TAG, "Headset disconnected");
                pause();
            }
        } else if (Intent.ACTION_MEDIA_BUTTON.equals(intentAction)) {
            final KeyEvent event = mediaButtonEvent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
            if (event == null) return super.onMediaButtonEvent(mediaButtonEvent);
            final int keycode = event.getKeyCode();
            final int action = event.getAction();
            final long eventTime = event.getEventTime();
            if (event.getRepeatCount() == 0 && action == KeyEvent.ACTION_DOWN) {
                switch (keycode) {
                    case KeyEvent.KEYCODE_HEADSETHOOK:
                        if (eventTime - mLastClickTime < DOUBLE_CLICK) {
                            playNext(mSongNumber);
                            mLastClickTime = 0;
                        } else {
                            if (isPlaying())
                                pause();
                            else resume();
                            mLastClickTime = eventTime;
                        }
                        break;
                    case KeyEvent.KEYCODE_MEDIA_STOP:
                        mTransportController.stop();
                        break;
                    case KeyEvent.KEYCODE_MEDIA_PLAY_PAUSE:
                        if (isMediaPlayerActive()) {
                            if (isPlaying()) mTransportController.pause();
                            else mTransportController.play();
                        }
                        break;
                    case KeyEvent.KEYCODE_MEDIA_NEXT:
                        mTransportController.skipToNext();
                        break;
                    case KeyEvent.KEYCODE_MEDIA_PREVIOUS:
                        mTransportController.skipToPrevious();
                        break;
                    case KeyEvent.KEYCODE_MEDIA_PAUSE:
                        mTransportController.pause();
                        break;
                    case KeyEvent.KEYCODE_MEDIA_PLAY:
                        mTransportController.play();
                        break;
                }
            }
        }
        return super.onMediaButtonEvent(mediaButtonEvent);
    }

    @Override
    public void onPlay() {
        super.onPlay();
        resume();
    }

    @Override
    public void onPause() {
        super.onPause();
        pause();
    }

    @Override
    public void onSkipToNext() {
        super.onSkipToNext();
        playNext(mSongNumber);
    }

    @Override
    public void onSkipToPrevious() {
        super.onSkipToPrevious();
        playPrevious(mSongNumber);
    }

    @Override
    public void onSeekTo(long pos) {
        super.onSeekTo(pos);
        seekTo(pos);
    }

    @Override
    public void onStop() {
        super.onStop();
        pause();
        commitMusicData();
        updatePlayingUI(STOP_ACTION);
        stopSelf();
    }
};

媒体按钮接收器清单条目

<!-- Media button receiver -->
    <receiver android:name=".receiver.MediaButtonReceiver" >
        <intent-filter>
            <action android:name="android.intent.action.MEDIA_BUTTON" />
            <action android:name="android.media.AUDIO_BECOMING_NOISY" />
        </intent-filter>
    </receiver>

几周以来我一直在尝试解决这个问题，但没有成功，并且迫切需要帮助。

编辑：MediaSessionCompat 的教程或示例也可以

虽然没有严格要求MediaSession, RemoteControlClient在 API14-19 设备上使用，确实需要音频焦点 http://developer.android.com/training/managing-audio/audio-focus.html并且 100% 强烈推荐用于所有媒体播放。

添加行，例如：

AudioManager audioManager = (AudioManager)
    getSystemService(Context.AUDIO_SERVICE);
int result = audioManager.requestAudioFocus(this,
    AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);
if (result != AudioManager.AUDIOFOCUS_GAIN) {
    return; //Failed to gain audio focus
}

在播放任何媒体之前，应获得音频焦点并显示控件。