/*
  * Extends this method to update check box states.
  */
 protected void doUpdateItem(Item item, Object element) {
   super.doUpdateItem(item, element);
   if (!item.isDisposed() && checkStateProvider != null) {
     setChecked(element, checkStateProvider.isChecked(element));
     setGrayed(element, checkStateProvider.isGrayed(element));
   }
 }