WPF 附加属性的类型被框架破坏

Question

考虑一些派生类型的几乎标准附件属性：

public class DerivedKeyBinding : KeyBinding
{
    public string Name; //shortened, make this propdp
}

public class KeyBindingExtenstions
{
    public static DerivedKeyBinding GetCommand(DependencyObject obj) {
        return (DerivedKeyBinding)obj.GetValue(CommandProperty);
    }

    public static void SetCommand(DependencyObject obj, DerivedKeyBinding value) {
        obj.SetValue(CommandProperty, value);
    }

    public static readonly DependencyProperty CommandProperty =
        DependencyProperty.RegisterAttached("Command", typeof(DerivedKeyBinding), typeof(KeyBindingExtenstions), new UIPropertyMetadata(null, CommandChanged));

    private static void CommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        var commandValue = GetCommand(d);
    }
}

稍后在XAML中设置：

<Grid>
    <Grid.Style>
        <Style>
            <Setter Property="local:KeyBindingExtenstions.Command">
                <Setter.Value>
                    <local:DerivedKeyBinding Name="{Binding Title, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"/>
                </Setter.Value>
            </Setter>
        </Style>
    </Grid.Style>
</Grid>

然而，这将在 var commandValue = GetCommand(d); 行崩溃，因为 local:DerivedKeyBinding 丢失到 KeyBinding 过程中的某个地方。
由于某些奇怪的原因，DerivedKeyBinding 类型的属性被设置为 KeyBinding 类型的值（即使值显式设置为 DerivedKeyBinding 在 XAML).

System.InvalidCastException: 'Unable to cast object of type 'System.Windows.Input.KeyBinding' to type 'AttachedPropertyInStyle.DerivedKeyBinding'.'

为什么会发生这种情况，我该如何解决这个问题？

问题似乎与 Name 绑定有关 - 如果它是静态值，代码将完美执行。

Answer 1

覆盖 KeyBinding.CreateInstanceCore. From Microsoft Docs:

Notes to Inheritors

Every Freezable derived class must implement this method. A typical implementation is to simply call the default constructor and return the result.

public class DerivedKeyBinding : KeyBinding
{
    ...

    protected override Freezable CreateInstanceCore()
    {
        return new DerivedKeyBinding();
    }
}

在 PropertyChangedCallback 中你也可以这样写：

var commandValue = (DerivedKeyBinding)e.NewValue;

WPF 附加属性的类型被框架破坏

WPF Attached Property's Type is being mangled by framework

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WPF 附加 属性 的类型被框架破坏

WPF Attached Property's Type is being mangled by framework

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WPF 附加属性的类型被框架破坏