Silverlight contextMenu 拖拽

Silverlight4 toolkit 提供了ContextMenu和MenuItem控件来实现右键菜单,下面是效果图

<Canvas x:Name="LayoutRoot">
<Border Height="30" Name="bType" Width="90" Canvas.Left="96" BorderThickness="1" BorderBrush="Gray" Background="Transparent" MouseLeftButtonDown="Border_MouseLeftButtonDown" MouseMove="Border_MouseMove" MouseLeftButtonUp="mouseLeftUp">
            <sdk:Label Name="lbSencond" HorizontalAlignment="Center" Content="类型" />
            <my:ContextMenuService.ContextMenu>
                <my:ContextMenu Name="TypeMenu" Background="Transparent">
                    <my:MenuItem Header="植物" Click="TypeMenu_Click">
                        <my:MenuItem.Icon>
                            <Image Width="16" Height="16" Source="images/zhiwu.jpg" />
                        </my:MenuItem.Icon>
                    </my:MenuItem>
                    <my:Separator />
                    <my:MenuItem Header="动物" Click="TypeMenu_Click">
                        <my:MenuItem.Icon>
                            <Image Width="16" Height="16" Source="images/dongwu.jpg" />
                        </my:MenuItem.Icon>
                    </my:MenuItem>
                </my:ContextMenu>
            </my:ContextMenuService.ContextMenu>
        </Border>
</Canvas>

下面是cs代码

 private bool isDrag;
        private Point startPoint;
        private Point endPoint;

        public MainPage()
        {
            InitializeComponent();
          
        }     

        private void TypeMenu_Click(object sender, RoutedEventArgs e)
        {
            MenuItem item = (MenuItem)sender;
            switch (item.Header.ToString())
            {
                case"动物":
                    MessageBox.Show(item.Header.ToString());
                    break;
                case"植物":
                    MessageBox.Show("类型是植物");
                    break;
                default:
                    break;
            }
            TypeMenu.IsOpen = false;
        }

        private void mouseLeftUp(object sender, MouseButtonEventArgs e)
        {
            isDrag = false; 
        }

       


        private void Border_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            Point p = e.GetPosition(LayoutRoot);
            SetDrag(p, bType);
        }

        private void Border_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDrag)
            {
                endPoint = e.GetPosition(LayoutRoot);
               
                Position(endPoint, bType);
            }
        }

        private void Position(Point end, UIElement uiName)
        {
            //计算X、Y轴起始点与终止点之间的相对偏移量
            double x = end.X - startPoint.X;
            double y = end.Y - startPoint.Y;

            Point positon = new Point((double)Canvas.GetLeft(uiName), (double)Canvas.GetTop(uiName));
            positon.X += x;
            positon.Y += y;

            Canvas.SetLeft(uiName, positon.X);
            Canvas.SetTop(uiName, positon.Y);
            startPoint = end;
        }

        private void SetDrag(Point start, UIElement uiName)
        {
            isDrag = true;
            startPoint = start;
            uiName.CaptureMouse();
        }