         }
         
         return cell
+    }
+}
+
+// MARK: UIScrollViewDelegate.
+
+extension _AssetCollectionViewController {
+    override func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        _backgroundFilterView.frame = CGRect(x: 0.0, y: min(0.0, collectionView!.contentOffset.y), width: tabNavigationController?.tabNavigationBar.bounds.width ?? 0.0, height: tabNavigationController?.tabNavigationBar.bounds.height ?? 0.0)
     }
 }
 

        
        // Fetch assets from asset collection.
        let option = PHFetchOptions()
        option.sortDescriptors = [NSSortDescriptor(key: "modificationDate", ascending: false)]
        _photoAssets = PHAsset.fetchAssets(in: _photoAssetCollection, options: option)
    }
    

}

fileprivate class _AssetCollectionViewController: UICollectionViewController {
    fileprivate var _backgroundFilterView: UIView = UIView()
    var _photoAssetCollection: PHAssetCollection!
    var _photoAssets: PHFetchResult<PHAsset>!
    
