WPF:在文本块顶部绘制

我希望能够绘制到TextBlock的顶部,并且已经找到了一种方法来实现这一点,但是一旦它出现,我就不能删除它。这是密码。

   public class DerivedTextBlock : TextBlock {

      public Boolean DrawExtra {
         get { return (Boolean)GetValue(DrawExtraProperty); }
         set { SetValue(DrawExtraProperty, value); }
      }

      // Using a DependencyProperty as the backing store for DrawExtra.  This enables animation, styling, binding, etc...
      public static readonly DependencyProperty DrawExtraProperty =
          DependencyProperty.Register("DrawExtra", typeof(Boolean), typeof(DerivedTextBlock), new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.AffectsArrange));

      public DrawingVisual DrawingVisual { get; set; }

      public DerivedTextBlock() {
         DrawingVisual = this.CreateDrawingVisualRectangle();
      }

      protected override int VisualChildrenCount {
         get {
            //if we want to draw our extra info, add one to
            // our visualChildrenCount, usually with a textblock it is 0
            if (DrawExtra) {
               return base.VisualChildrenCount + 1;
            }
            else {
               return base.VisualChildrenCount;
            }
         }
      }

      protected override Visual GetVisualChild(int index) {
         return DrawingVisual;
      }

      // Create a DrawingVisual that contains a rectangle.
      private DrawingVisual CreateDrawingVisualRectangle() {
         DrawingVisual drawingVisual = new DrawingVisual();

         // Retrieve the DrawingContext in order to create new drawing content.
         DrawingContext drawingContext = drawingVisual.RenderOpen();

         // Create a rectangle and draw it in the DrawingContext.
         Rect rect = new Rect(new Point(10.0, 0), new Size(10.0 / 2.0, 10));
         drawingContext.DrawRectangle(Brushes.LightBlue, (Pen)null, rect);

         // Persist the drawing content.
         drawingContext.Close();

         return drawingVisual;
      }
   }

我这么做的原因是:我们有一个数据网格,有很多单元格,每个单元格都显示文本。我们在单元格上显示一些验证信息,并通过使用一个带有文本块的模板和网格中的一些路径来实现。这样做的开销会向可视化树中添加额外的元素,当我们必须重新绘制(在加载、切换窗口或排序时)时,可视化树中的元素越多,花费的时间就越长。当它只是一个textblock时,它比使用网格控件快大约1/3-1/2。所以我们想在文本框的顶部绘制验证内容。