public void Show(ListViewItem item, bool before)
 {
   Hide();
   fItem = item;
   fAdorner = new InsertionMarkAdorner(fItem, before);
 }
 public void Hide()
 {
   if(fAdorner != null)
   {
     fAdorner.Close(fItem);
     fAdorner = null;
     fItem = null;
   }
 }
 public InsertionMark()
 {
   fAdorner = null;
   fItem = null;
 }