void ConstrainToItemsView()
        {
            var itemsViewWidth  = ItemsView.Width;
            var itemsViewHeight = ItemsView.Height;

            if (itemsViewHeight < 0 || itemsViewWidth < 0)
            {
                ItemsViewLayout.UpdateConstraints(CollectionView.Bounds.Size);
                return;
            }

            ItemsViewLayout.UpdateConstraints(new CGSize(itemsViewWidth, itemsViewHeight));
        }