protected override void OnSizeRequested(ref Requisition requisition)
{
// make request to root
if (root != null && root.Visible)
{
requisition = root.SizeRequest();
}
else
{
requisition.Width = requisition.Height = 0;
}
requisition.Width += 2 * (int)BorderWidth;
requisition.Height += 2 * (int)BorderWidth;
}