Wpf INotifyPropertyChanged实现双向绑定的小测试。似乎是绑定失败。请教一下代码是哪里没有写对呢？

Question

学习后尝试练习一下发现 Test的事件PropertyChanged始终为空。请问一下我写的代码哪里需要修改呢，现在的问题是什么原因。我感觉是自己binding 的path没写对，或者是datacontext没对。因为这两个我不知道该怎样写，该写在哪里？

<Window x:Class="WpfApplication3.MainWindow"
        Name="winM"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TextBlock x:Name="txt2" Background="Yellow" Text="{Binding Path = this.A , Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" TextWrapping="Wrap" Margin="33,127,32,92" />
        <Button Content="Button" HorizontalAlignment="Left" Margin="140,263,0,0" VerticalAlignment="Top" Width="115" Height="47" Click="Button_Click"/>
        <Button Content="Button" HorizontalAlignment="Left" Margin="334,263,0,0" VerticalAlignment="Top" Width="115" Height="43" Click="Button_Click_1"/>
    </Grid>
</Window>

//cs代码

namespace WpfApplication3
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {

            InitializeComponent();

            test = new Test();
            this.txt2.DataContext = test;

        }
        public Test test;
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            test.A = "1111111111";
        }
        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            test.A = "22222222222";
        } 

    }
    public class Test : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private string a;
        public string A
        {
            get { return a; }
            set
            {
                a = value;
                if (this.PropertyChanged != null)
                {
                    this.PropertyChanged.Invoke(this, new PropertyChangedEventArgs("A"));
                }
            }
        }
    }
}

Answer 1

https://blog.csdn.net/crf_moonlight/article/details/80879637