Question

I’ve got a somewhat special problem: I have a markup extension that needs to check an attached property. The attached property is defined as inheritable.

This works properly in XAML for all elements that are defined under a Window/UserControl, but not for resources. For example, given this XAML:

<Window MyAttachedProp="...">
    <Window.Resources>
        <FlowDocument x:Key="Doc">
            <Paragraph><Run Text="{MyMarkupExtension}" /></Paragraph>
        </FlowDocument>
    </Window.Resources>

    <FlowDocumentScrollViewer Document="{StaticResource Doc}" />
    ...
</Window>

The markup extension fails because when the ProvideValue()-function is called, the attached property is not derived from the Window to the FlowDocument and to the Run.

Is there same workaround to make this work?

Thanks,
Steven

Answer 1

From Inheriting Property Values Across Tree Boundaries:

Property inheritance works by traversing a tree of elements. This tree
is often parallel to the logical tree

Apparently a resource dictionary does not constitute an element tree and hence the value won’t be inherited. However, i guess it should work when you set the property on the FlowDocument, since that is the root of an element tree:

<Window.Resources>
    <FlowDocument x:Key="Doc" MyAttachedProp="...">
        <Paragraph><Run Text="{MyMarkupExtension}" /></Paragraph>
    </FlowDocument>
</Window.Resources>