关于DataContext的

请问我书上的（2）怎么用？我自己写了一段代码 但没显示 该怎么改？或者你们写一段代码给我看看 谢谢了 高分献上
书上的内容：

我的代码是这样的
XAML代码是这样的 我在项目里新建了一个窗口Window1
<Window x:Class="WpfApplication5.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Grid>
<TextBox Text="{Binding Id}"/>
</Grid>
</Window>
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MainWindow的Xaml代码是这样的：
<Window x:Class="WpfApplication5.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:WpfApplication5"
Title="MainWindow" Height="350" Width="525">
<StackPanel>
<StackPanel.DataContext>
<sys:Student Id="6"/>
</StackPanel.DataContext>
<Button Click="Button_Click_1"/>
</StackPanel>
</Window>
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C#后台代码是这样的：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication5
{
/// <summary>
/// MainWindow.xaml 的交互逻辑
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}

private void Button_Click_1(object sender, RoutedEventArgs e)
{
Window1 a = new Window1();
a.ShowDialog();
}
}
public class Student
{
public int Id { get; set; }
}
}