private void RefreshThumbnail(TaskbarButtonThumbnail thumbnail)
 {
     if (parent != null && thumbnail.ChildWindow != null)
     {
         TaskbarList.SetTabProperties(thumbnail.ChildWindow, thumbnail.flag);
     }
 }
        private void RegisterThumbnail(TaskbarButtonThumbnail thumbnail)
        {
            var idx = IndexOf(thumbnail);
            var nxt = idx < Count - 1 ? this[idx + 1] : null;

            if (parent != null && thumbnail.ChildWindow != null)
            {
                TaskbarList.RegisterTab(parent, thumbnail.ChildWindow);
                TaskbarList.SetTabOrder(thumbnail.ChildWindow, nxt?.ChildWindow);
                TaskbarList.SetTabProperties(thumbnail.ChildWindow, thumbnail.flag);
            }
        }