protected override void OnVisibleChanged (EventArgs e)
{
base.OnVisibleChanged (e);
if (owner_item != null && owner_item is ToolStripDropDownItem) {
ToolStripDropDownItem dropdown_owner = (ToolStripDropDownItem)owner_item;
if (Visible)
dropdown_owner.OnDropDownOpened (EventArgs.Empty);
else
dropdown_owner.OnDropDownClosed (EventArgs.Empty);
}
}