private void OpenDropDown(bool oldValue, bool newValue)
{
if(DropDownPopup != null)
{
DropDownPopup.IsOpen = true;
}
_popupHasOpened = true;
#if SILVERLIGHT
OnDropDownOpened(new RoutedPropertyChangedEventArgs<bool>(oldValue, newValue));
#else
OnDropDownOpened(new RoutedPropertyChangedEventArgs<bool>(oldValue, newValue, DropDownOpenedEvent));
#endif
}