protected virtual void OnDismissPopup(RibbonDismissPopupEventArgs e)
{
UIElement popupChild = _popup.TryGetChild();
RibbonHelper.HandleDismissPopup(e,
delegate(bool value) { IsDropDownOpen = value; },
delegate(DependencyObject d) { return d == _partToggleButton; },
popupChild,
this);
}