silverlight RenderTransform 后台动画设置

            myBall.RenderTransform = new TranslateTransform();
            Storyboard sb = new Storyboard();
            DoubleAnimation da = new DoubleAnimation();
            da.From = 0;
            da.To = 1000;
            da.RepeatBehavior = RepeatBehavior.Forever;
            da.Duration = new Duration(new TimeSpan(0, 0, 2));
            Storyboard.SetTarget(da, myBall);
            Storyboard.SetTargetProperty(da, new PropertyPath("(FrameworkElement.RenderTransform).(TranslateTransform.X)"));
            sb.Children.Add(da);
            //myBall.Resources.Add("sb1", sb);
            sb.Begin();