TextBox绑定到一个类实例属性时失败

Question

环境是vs2010+wpf 4.0

相关代码如下（插入代码后会失去格式，试过几次均如此）：

<Page x:Class="WpfBrowserApplication1.Page1"    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"    mc:Ignorable="d"    d:DesignHeight="300"    d:DesignWidth="300"    Title="Page1">  <Grid>    <TextBox Height="23" HorizontalAlignment="Left" Margin="59,69,0,0" Name="textBox1" VerticalAlignment="Top" Width="176"/>    <Button Content="Button1" Height="23" HorizontalAlignment="Left" Margin="105,0,0,90" Name="button1" VerticalAlignment="Bottom" Width="75" Click="button1_Click" />    <Button Content="Button2" Height="23" HorizontalAlignment="Left" Margin="206,187,0,0" Name="button2" VerticalAlignment="Top" Width="75" Click="button2_Click" />    <Button Content="Button3" Height="23" HorizontalAlignment="Left" Margin="16,187,0,0" Name="button3" VerticalAlignment="Top" Width="75" Click="button3_Click" />  </Grid></Page>

namespace WpfBrowserApplication1{  /// <summary>   /// Interaction logic for Page1.xaml   /// </summary>   public partial class Page1 : Page  {    public sub s { get; set; }    public Page1()    {      InitializeComponent();    }    private void button1_Click(object sender, RoutedEventArgs e)    {      s = new sub();      Binding b = new Binding();      b.Path = new PropertyPath("Name");      b.Source = s;      b.Mode = BindingMode.TwoWay;      textBox1.SetBinding(TextBox.TextProperty, b);      s.Name = "init";    }    private void button2_Click(object sender, RoutedEventArgs e)    {      textBox1.Text = "button2";      MessageBox.Show(s.Name);    }    private void button3_Click(object sender, RoutedEventArgs e)     {       s.Name = "button3";       MessageBox.Show(textBox1.Text);     }  }  public class sub   {     public string Name { get; set; }   }}

在通过单击button1绑定后，不论是修改源数据还是目标对象数据，都不能同步。