void FetchBitmapFromURL(string bitmapUrl, Notification.Builder builder)
 {
     AlbumArtCache.Instance.Fetch (bitmapUrl, new AlbumArtCache.FetchListener () {
         OnFetched = (artUrl, bitmap, icon) => {
             if (metadata != null && metadata.Description != null &&
                 artUrl == metadata.Description.IconUri.ToString ()) {
                 LogHelper.Debug (Tag, "fetchBitmapFromURLAsync: set bitmap to ", artUrl);
                 builder.SetLargeIcon (bitmap);
                 notificationManager.Notify (NotificationId, builder.Build ());
             }
         }
     });
 }