WPF设计界面添加后台代码

<Window x:Class="WpfApplication2.MainWindow"
        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"
        xmlns:local="clr-namespace:WpfApplication2"
        xmlns:sys="clr-namespace:System;assembly=mscorlib"
        mc:Ignorable="d"
        Title="MainWindow" Height="800" Width="500">

    <Grid VerticalAlignment="Center" HorizontalAlignment="Center">
         <Button x:Name="button" Content="Button" HorizontalAlignment="Left" Margin="-150,-165,0,0" VerticalAlignment="Top" Width="85" Click="button_Click"/>
        <TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="-150,-75,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
    </Grid>
  
    <x:Code>
        <!--此处可以写后台代码-->
        <![CDATA[
         private void button_Click(object sender, RoutedEventArgs e)
        {
            test();
            string test_message = "dddddd";
            textBox.Text = test_message;
        }
   ]]>
    </x:Code>
</Window>

        public void test()
        {
            string mes = "test message";
            MessageBox.Show(mes);
        }