             "collectionView":collectionView]
         
         let metrics:[String:CGFloat] = [
-            "borderHeight":kBorderHeight]
+            "borderHeight":kBorderHeight,
+            "collectionHeight":kMaxHeight]
         
         addConstraints(NSLayoutConstraint.constraints(
             withVisualFormat:"H:|-0-[border]-0-|",

            metrics:metrics,
            views:views))
        addConstraints(NSLayoutConstraint.constraints(
            withVisualFormat:"V:|-0-[collectionView]-0-|",
            options:[],
            metrics:metrics,
            views:views))

    private let kMaxHeight:CGFloat = 200
    private let kCellWidth:CGFloat = 50
    private let kFooterHeight:CGFloat = 70
    private let kAnimationDuration:TimeInterval = 6
    
    init(controller:CChat)
    {
