         let count = 0
         return count
     }
+    
+    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
+        return UICollectionViewCell()
+    }
 }

            action:#selector(actionBack(sender:)),
            for:UIControlEvents.touchUpInside)
        
        addSubview(backButton)
        
        let views:[String:UIView] = [
            "backButton":backButton]
        
        let metrics:[String:CGFloat] = [:]
        

            metrics:metrics,
            views:views))
        addConstraints(NSLayoutConstraint.constraints(
            withVisualFormat:"H:|-0-[border]-0-|",
            options:[],
            metrics:metrics,
            views:views))
        addConstraints(NSLayoutConstraint.constraints(
            withVisualFormat:"V:|-0-[backButton(64)]",
            options:[],
            metrics:metrics,
            views:views))
        addConstraints(NSLayoutConstraint.constraints(
            withVisualFormat:"V:[border(1)]-0-|",
            options:[],
            metrics:metrics,
            views:views))
