Sliverlight 拖动控件事件

bool trackingMouseMove = false;
        Point mousePosition;

        void OnMouseDown(object sender, MouseButtonEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
            mousePosition = e.GetPosition(null);
            trackingMouseMove = true;
            if (null != element)
            {
                element.CaptureMouse();
                element.Cursor = Cursors.Hand;
            }
        }

        void OnMouseMove(object sender, MouseEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
            if (trackingMouseMove)
            {
                double deltaV = e.GetPosition(null).Y - mousePosition.Y;
                double deltaH = e.GetPosition(null).X - mousePosition.X;
                double newTop = deltaV + (double)element.GetValue(Canvas.TopProperty);
                double newLeft = deltaH + (double)element.GetValue(Canvas.LeftProperty);

                element.SetValue(Canvas.TopProperty, newTop);
                element.SetValue(Canvas.LeftProperty, newLeft);

                mousePosition = e.GetPosition(null);
            }
        }

        void OnMouseUp(object sender, MouseButtonEventArgs e)
        {
            FrameworkElement element = sender as FrameworkElement;
            trackingMouseMove = false;
            element.ReleaseMouseCapture();

            mousePosition.X = mousePosition.Y = 0;
            element.Cursor = null;
        }