public virtual void SwapByIndex(int index1, int index2)
 {
     _items.SwapByIndex(index1, index2);
     _keys.SwapByIndex(index1, index2);
     if (CollectionChanged != null)
     {
         CollectionChanged(this, new EventArgs());
     }
 }
 public virtual void SwapByIndex(int index1, int index2)
 {
     _coll.SwapByIndex(index1, index2);
 }