为什么绑定没有生效[重复]

Question

我创建了 TextBox 类的派生类 MyTextBox，并添加了一个名为 AString 的依赖属性和一个名为 ContextChangedEvent 的路由事件。在XAML代码中，Text属性绑定到AString属性，但是当我更改Text属性的值时，AString属性的setter没有被触发，这意味着绑定没有生效。这是为什么？

public class MyTextBox : TextBox
{
    public static readonly RoutedEvent ContentChangedEvent;
    public event RoutedEventHandler ContentChanged
    {
        add { AddHandler(ContentChangedEvent, value); }
        remove { RemoveHandler(ContentChangedEvent, value); }
    }

    public string AString
    {
        get { return (string)GetValue(AStringProperty); }
        set
        {
            SetValue(AStringProperty, value);
            OnContentChanged();
        }
    }

    public static readonly DependencyProperty AStringProperty;

    static MyTextBox()
    {
        ContentChangedEvent = EventManager.RegisterRoutedEvent("ContentChanged", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(MyTextBox));
        var a = new FrameworkPropertyMetadata("555");
        a.BindsTwoWayByDefault = true;
        AStringProperty = DependencyProperty.Register("AString", typeof(string), typeof(MyTextBox), a);
    }
    private void OnContentChanged()
    {
        RaiseEvent(new RoutedEventArgs(ContentChangedEvent, this));
    }

 <local:MyTextBox x:Name="mtb1"
                  ContentChanged="MyTextBox_ContentChanged"
                  Text="{Binding AString,
                                 RelativeSource={RelativeSource Mode=Self},
                                 Mode=TwoWay}" />

我尝试将绑定模式更改为双向绑定，但没有成功

Answer 1

CLR 属性只是依赖属性的代理包装器。除了获取和设置属性值之外，该包装器中不应该有任何逻辑。
这是正确的实现：

    public class MyTextBox : TextBox
    {
        public event RoutedEventHandler ContentChanged
        {
            add { AddHandler(ContentChangedEvent, value); }
            remove { RemoveHandler(ContentChangedEvent, value); }
        }
        public static readonly RoutedEvent ContentChangedEvent
            = EventManager.RegisterRoutedEvent(
                nameof(ContentChanged),
                RoutingStrategy.Bubble,
                typeof(RoutedEventHandler),
                typeof(MyTextBox));

        public string AString
        {
            get => (string)GetValue(AStringProperty);
            set => SetValue(AStringProperty, value);// OnContentChanged();
        }

        public static readonly DependencyProperty AStringProperty
            = DependencyProperty.Register(
                nameof(AString),
                typeof(string),
                typeof(MyTextBox),
                new FrameworkPropertyMetadata("555")
                {
                    BindsTwoWayByDefault = true,
                    PropertyChangedCallback = OnContentChanged
                });
        private static void OnContentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
           ((UIElement)d).RaiseEvent(new RoutedEventArgs(ContentChangedEvent, d));
        }
    }