为什么在 ImageSource 上设置 TemplateBinding 会引发 KeyNotFoundException？

Question

我有以下ListBox 子类...

public class ImageAnnotationEditor : ListBox {

    static ImageAnnotationEditor() {

        DefaultStyleKeyProperty.OverrideMetadata(
            typeof(ImageAnnotationEditor),
            new FrameworkPropertyMetadata(typeof(ImageAnnotationEditor)));
    }

    #region ImageSource Property

        public static readonly DependencyProperty ImageSourceProperty = Image.SourceProperty.AddOwner(
            typeof(ImageAnnotationEditor));

        public ImageSource? ImageSource {
            get => (ImageSource)GetValue(ImageSourceProperty);
            set => SetValue(ImageSourceProperty, value);
        }

    #endregion ImageSource Property
}

使用以下模板...

<ControlTemplate TargetType="{x:Type c:ImageAnnotationEditor}">

    <Border
        Background="{TemplateBinding Background}"
        BorderBrush="{TemplateBinding BorderBrush}"
        BorderThickness="{TemplateBinding BorderThickness}">

        <Viewbox Stretch="Uniform"
            HorizontalAlignment="Center"
            VerticalAlignment="Center">

            <c:LayerPanel>
                <Image Source="{TemplateBinding ImageSource}" />   <-- This line causes the problem
                <StackPanel IsItemsHost="True" />
            </c:LayerPanel>

        </Viewbox>

    </Border>

</ControlTemplate>

当我运行应用程序时，它会抛出以下内容...

System.Collections.Generic.KeyNotFoundException: 'The given key was not present in the dictionary.'

如果我从ControlTemplate 中删除Source="{TemplateBinding ImageSource}"，它会运行而不会崩溃，但当然不会显示图像。

Answer 1

不知道为什么会抛出 KeyNotFoundException，但是如果您注册一个新的 DependencyProperty，而不是向 Image.SourceProperty 添加所有者类型，则 TemplateBinding 会起作用。这也将避免对 Image 类的依赖。

public static readonly DependencyProperty ImageSourceProperty =
   DependencyProperty.Register(
       nameof(ImageSource), typeof(ImageSource), typeof(ImageAnnotationEditor));

---

否则，请使用通常的解决方法，即将 TemplateBinding 替换为 RelativeSource TemplatedParent 的常规 Binding：

<Image Source="{Binding ImageSource,
                RelativeSource={RelativeSource TemplatedParent}}"/>