MediaControllerCompat's getMetadata returns null

Question

I'm trying to make a audio app in Android using this video as a guide, and I'm having trouble with creating the notification using the audio's metadata.

Here is the code I use to extract the audio files from the device:

public void loadData() {
    ContentResolver contentResolver = context.getContentResolver();

    String selection = Media.IS_MUSIC + "!= 0";
    String[] projection = {
        Media._ID,
        Media.ARTIST,
        Media.TITLE,
        Media.DISPLAY_NAME,
        Media.DURATION,
        Media.ALBUM
    };

    Cursor cursor = contentResolver.query(
        Media.EXTERNAL_CONTENT_URI, projection, selection, null, null
    );

    if(cursor == null || !cursor.moveToFirst()) return;
    else {
        int size = cursor.getCount();
        metadata = new ArrayList<>(size);
        mediaItems = new ArrayList<>(size);
    }

    int
        idIndex          = cursor.getColumnIndex(Media._ID),
        artistIndex      = cursor.getColumnIndex(Media.ARTIST),
        titleIndex       = cursor.getColumnIndex(Media.TITLE),
        displayNameIndex = cursor.getColumnIndex(Media.DISPLAY_NAME),
        durationIndex    = cursor.getColumnIndex(Media.DURATION),
        albumIndex       = cursor.getColumnIndex(Media.ALBUM);

    do {
        String mediaId = cursor.getString(idIndex);
        MediaMetadataCompat data = new MediaMetadataCompat.Builder()
            .putString(MediaMetadataCompat.METADATA_KEY_MEDIA_ID, cursor.getString(idIndex))
            .putString(MediaMetadataCompat.METADATA_KEY_ALBUM, cursor.getString(albumIndex))
            .putString(MediaMetadataCompat.METADATA_KEY_ARTIST, cursor.getString(artistIndex))
            .putString(MediaMetadataCompat.METADATA_KEY_TITLE, cursor.getString(titleIndex))
            .putString(MediaMetadataCompat.METADATA_KEY_DISPLAY_TITLE, cursor.getString(displayNameIndex))
            .putLong(MediaMetadataCompat.METADATA_KEY_DURATION, cursor.getLong(durationIndex))
            .build();

        metadata.add(data);
        mediaItems.add(new MediaBrowserCompat.MediaItem(
            data.getDescription(),
            MediaItem.FLAG_PLAYABLE
        ));
    } while(cursor.moveToNext());

    cursor.close();
}

public List<MediaItem> getMediaItems() {
    return mediaItems;
}

And here's my MediaBrowserService's onLoadChildren code:

@Override
public void onLoadChildren(@NonNull String parentId,
                           @NonNull Result<List<MediaBrowserCompat.MediaItem>> result
) {
    if(parentId.equals(MEDIA_ROOT_ID)) {
        result.sendResult(source.getMediaItems());
    }
}

And lastly, the code throwing the error (I call createNotifcation() after creating the MediaSession and setActive(true)):

private void createNotification() {
    NotificationCompat.Action playAction = new NotificationCompat.Action(
        android.R.drawable.ic_media_play,
        getString(R.string.play),
        MediaButtonReceiver.buildMediaButtonPendingIntent(
            ExoMusicService.this,
            PlaybackStateCompat.ACTION_PLAY
        )
    );
    NotificationCompat.Action pauseAction = new NotificationCompat.Action(
        android.R.drawable.ic_media_pause,
        getString(R.string.pause),
        MediaButtonReceiver.buildMediaButtonPendingIntent(
            ExoMusicService.this,
            PlaybackStateCompat.ACTION_PAUSE
        )
    );
    MediaControllerCompat controller = mediaSession.getController();
    Log.i(LOG_TAG, "createNotification: " + (controller == null)); // false
    MediaMetadataCompat metadata = controller.getMetadata();
    Log.i(LOG_TAG, "createNotification: " + (metadata == null)); // true
    MediaDescriptionCompat description = metadata.getDescription();

    notification = new NotificationCompat.Builder(ExoMusicService.this, PLAYBACK_CHANNEL_ID)
        .setContentTitle(description.getTitle())
        .setContentText(description.getSubtitle())
        .setContentIntent(controller.getSessionActivity())
        .setStyle(
            new MediaStyle()
                .setShowActionsInCompactView(0)
                .setMediaSession(mediaSession.getSessionToken())
                .setShowCancelButton(true)
        )
        .setDeleteIntent(MediaButtonReceiver.buildMediaButtonPendingIntent(
            ExoMusicService.this,
            PlaybackStateCompat.ACTION_STOP
        ))
        .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
        .addAction(playerManager.isPlaying()? pauseAction : playAction)
        .setSmallIcon(R.drawable.icon)
        .build();
}

If I understood correctly, I believe that's all the code relating to this issue. Any idea as to what I could be overlooking?

Answer 1

Before show notification you should call mediaSession.setMetadata(/* your metadata */).

Metadata should contains information about current music item, which is playing (or preparing, paused, ect.).

Please refer to the documentation for details.