     // MARK: - Transitions
     /*-------------------------------------------------------------------------------*/
     
+    public var layoutConstraintConfiguration : ((_ container: NSViewController, _ controller: CollectionViewPreviewController)->Void)?
+    
     /**
      The duration of present/dismiss transitions
      */

        return cell!
    }
    
    // MARK: - Interactive Gesture
    /*-------------------------------------------------------------------------------*/
    

        
        controller.addChildViewController(self)
        controller.view.addSubview(self.view)
        if let config = self.layoutConstraintConfiguration {
            config(controller, self)
        }
        else {
            self.view.addConstraintsToMatchParent()
        }
        
        self.collectionView.reloadData()
        
