private void RemoveDisabledItem(DisabledItem targetItem)
 {
     if (targetItem != null)
     {
         _disabledItems.Remove(targetItem);
     }
 }
 private void AddDisabledItem(object item, DisabledItem targetItem)
 {
     if (targetItem == null)
     {
         bool isChecked = this.CheckedItems.Contains(item);
         var  addItem   = new DisabledItem {
             Item = item, Checked = isChecked
         };
         _disabledItems.Add(addItem);
     }
 }
 private void RefreshItems(object item, bool enabled, DisabledItem targetItem)
 {
     if (enabled)
     {
         RemoveDisabledItem(targetItem);
     }
     else
     {
         AddDisabledItem(item, targetItem);
     }
     this.Refresh();
 }