         addSubview(collectionView)
         addSubview(viewBar)
         
-        NSLayoutConstraint.topToTop(
+        layoutBarTop = NSLayoutConstraint.topToTop(
             view:viewBar,
             toView:self)
         NSLayoutConstraint.height(

class VCreate:View, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
{
    private(set) weak var collectionView:VCollection!
    private let kBarHeight:CGFloat = 64
    private let kCollectionBottom:CGFloat = 40
    

    }
    
    //MARK: collectionView delegate
    
    func scrollViewDidScroll(_ scrollView:UIScrollView)
    {
        let offsetY:CGFloat = scrollView.contentOffset.y
        let usableOffset:CGFloat
        
        if offsetY < 0
        {
            usableOffset = 0
        }
        else
        {
            usableOffset = -offsetY
        }
        
        layoutBarTop.constant = usableOffset
    }
    
    func collectionView(_ collectionView:UICollectionView, layout collectionViewLayout:UICollectionViewLayout, sizeForItemAt indexPath:IndexPath) -> CGSize
    {
