     }
 }
 
+// MARK: - _AssetsViewController.
+
 fileprivate class _AssetsViewController: UICollectionViewController {
     fileprivate var _backgroundFilterView: UIView = UIView()
+    fileprivate var _isViewDidAppear: Bool = false
+    fileprivate weak var _captureVideoPreviewCell: _AssetsCaptureVideoPreviewCollectionCell?
     var _photoAssetCollection: PHAssetCollection!
+    
     var _photoAssets: PHFetchResult<PHAsset>!
     var imagePickerController: TabNavigationImagePickerController { return tabNavigationController as! TabNavigationImagePickerController }
+    
     
     convenience init(collectionViewLayout layout: UICollectionViewLayout, photoAlbum assetCollection: PHAssetCollection) {
         self.init(collectionViewLayout: layout)

        setTabNavigationTitle(["title": _photoAssetCollection.localizedTitle ?? "", "range": 0..<2])
        // Register asset collection cell.
        collectionView!.register(_AssetsCollectionCell.self, forCellWithReuseIdentifier: String(describing: _AssetsCollectionCell.self))
        
        collectionView!.contentInset = UIEdgeInsets(top: tabNavigationController!.tabNavigationBar.bounds.height, left: 0.0, bottom: 0.0, right: 0.0)
        collectionView!.scrollIndicatorInsets = collectionView!.contentInset

    }
}

// MARK: CollectionViewController Delegate And DataSource Supporting.

extension _AssetsViewController {
    override func numberOfSections(in collectionView: UICollectionView) -> Int {
