Blend生成的TransformGroup如何引用?

很多时候，blend在制作动画时，会自动为对象生成如下代码:

<Rectangle Fill="White" Stroke="Black" HorizontalAlignment="Center" VerticalAlignment="Center" Width="300" Height="30" RenderTransformOrigin="0.5,0.5" x:Name="rect">
    <Rectangle.RenderTransform>
     <TransformGroup>
      <ScaleTransform/>
      <SkewTransform/>
      <RotateTransform/>
      <TranslateTransform/>
     </TransformGroup>
    </Rectangle.RenderTransform>
   </Rectangle>

如果想在cs代码中动态控制，就得先知道如何引用它们，在不借助x:Name的情况下，可以这么做: 

private void Button_Click(object sender, RoutedEventArgs e)
        {            

            RotateTransform r = (rect.RenderTransform as TransformGroup).Children[2] as RotateTransform;

            DoubleAnimation dblAnim = new DoubleAnimation() { Duration = TimeSpan.FromSeconds(1), To = 135.0, EasingFunction = new BackEase() { EasingMode = EasingMode.EaseInOut } };         

            Storyboard.SetTarget(dblAnim, r);
            Storyboard.SetTargetProperty(dblAnim, new PropertyPath(RotateTransform.AngleProperty));

            Storyboard sb = new Storyboard();
            sb.Children.Add(dblAnim);           
            sb.AutoReverse = true;
            sb.Begin();           

        }
    }

上面的代码，将生成一段动画：1秒钟内将矩形旋转135度