public void Reduce()
 {
     if (ParentGroup != null && dockObjects.Count == 1)
     {
         DockObject obj = dockObjects [0];
         int        n   = ParentGroup.GetObjectIndex(this);
         ParentGroup.dockObjects [n] = obj;
         obj.ParentGroup             = ParentGroup;
         obj.CopySizeFrom(this);
         dockObjects.Clear();
         ResetVisibleGroups();
         ParentGroup.ResetVisibleGroups();
     }
 }