private void AdjustScroll()
{
if (VisibleItems == null)
return;
if (oldItemCount == VisibleItems.Count)
return;
var needHeight = ItemHeight*VisibleItems.Count + 1;
Height = Math.Min(needHeight, MaximumSize.Height);
AutoScrollMinSize = new Size(0, needHeight);
oldItemCount = VisibleItems.Count;
}