//给任务栏的Popup界面缩略图应用圆角
   Border visualBorder = new Border
    {
       BorderBrush = Brushes.Transparent,
       BorderThickness = new Thickness(1),
       CornerRadius = new CornerRadius(10),
       Margin = new Thickness(10),
       Height = 150D,
       Width = 270D,
       Child = emptyRectangle,
       HorizontalAlignment = HorizontalAlignment.Center,
       VerticalAlignment = VerticalAlignment.Center,
       Background = this.FindResource("transparentColor") 

                     as LinearGradientBrush
     };
 //对任务栏的Popup界面缩略图的背景应用圆角
   Border host = new Border
    {
       BorderBrush = Brushes.Transparent,
       BorderThickness = new Thickness(1),
       CornerRadius = new CornerRadius(8),
       Child = visualBorder,
       HorizontalAlignment = HorizontalAlignment.Center,
       VerticalAlignment = VerticalAlignment.Center,
       Background = this.FindResource("thumbnailBackground") 

                          as ImageBrush
    };

 //添加一ToolTip，用来宿主子界面的宿略图
  ToolTip visualToolTip = new ToolTip
  {
      Content = host,
      Background = Brushes.Transparent,
      BorderBrush = Brushes.Transparent,
      Placement = PlacementMode.Top,
      HorizontalContentAlignment = HorizontalAlignment.Center,
      VerticalContentAlignment = VerticalAlignment.Center,
      HasDropShadow = false,
      VerticalOffset=3
  };
 //设计ToolTip的Popup延迟时间为20ms
 ToolTipService.SetInitialShowDelay(thumbnail, 20);
 thumbnail.ToolTip = visualToolTip;

//当打开的子界面关闭时需从任务栏移除此界面在任务栏上的图标
  child.Closed += delegate
   {
     this.statusBar.Children.Remove(hostBorder);
   };
//在任务栏上单击任务图标时，最大化或者最小化子界面
  hostBorder.MouseLeftButtonDown += delegate(object sender, MouseButtonEventArgs e)
    {
      if (e.ClickCount == 1)
         {
           if (child.WindowState == WindowState.Minimized)
             {
                //正常显示子界面
                   child.WindowState = WindowState.Normal;
                 child.Topmost = true;
             }
            else
                //最小化子界面
                  child.WindowState = WindowState.Minimized;
         }
    };