silverlight ScrollViewer 스크롤 막대에 응답 마우스 휠 추가

<UserControl x:Class="SilverlightApplication54.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">


    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="50"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        <Button Name="TestButton" Width="200" Height="24" Content="Add" Grid.Row="0"></Button>
        <ScrollViewer Name="TestScrollViewer" Grid.Row="1">
            <StackPanel Name="TestStackPanel" Orientation="Vertical">
            </StackPanel>
        </ScrollViewer>
    </Grid>
</UserControl>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;


namespace SilverlightApplication54
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            TestButton.Click += new RoutedEventHandler(TestButton_Click);
            this.MouseWheel += new MouseWheelEventHandler(MainPage_MouseWheel);
        }
        /// <summary>
        ///       ，ScrollViewer             。
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void MainPage_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            ScrollViewer viewer = TestScrollViewer;
            if (viewer == null)
                return;
            double num = Math.Abs((int)(e.Delta / 2));
            double offset = 0.0;
            if (e.Delta > 0)
            {
                offset = Math.Max((double)0.0, (double)(viewer.VerticalOffset - num));
            }
            else
            {
                offset = Math.Min(viewer.ScrollableHeight, viewer.VerticalOffset + num);
            }
            if (offset != viewer.VerticalOffset)
            {
                viewer.ScrollToVerticalOffset(offset);
                e.Handled = true;
            }
        }
        void TestButton_Click(object sender, RoutedEventArgs e)
        {
            //  TextBox
            TextBox textBox = new TextBox();
            textBox.Width = 200;
            textBox.Height = 100;
            TestStackPanel.Children.Add(textBox);
        }
    }
}