protected override bool OnButtonReleaseEvent(Gdk.EventButton ev)
{
pressed = false;
if (selected_item == null)
return base.OnButtonReleaseEvent (ev);
Gdk.Point pt = new Gdk.Point ((int)ev.X, (int)ev.Y);
if (selected_item.Bounds.Contains (pt))
selected_item.OnActivated ();
return base.OnButtonReleaseEvent (ev);
}