Page.Datacontext Not Inherited from Parent Frame

page.DataContext not inherited from parent Frame?

To answer your question about documentation of this behavior: It's not Microsoft documentation, but I have a couple of WPF books that both mention this.

"Essential Windows Presentation Foundation" says: (pp. 160-161)

There are two interesting models for hosting navigable content: isolated hosting and integrated hosting.

With isolated hosting the content is not trusted and is run in a completely isolated (sandboxed) environment. This is how WPF content is hosted when running in the system Web browser as a XAML Browser Application. For navigation to another application or HTML content, this isolated hosting model is supported with a Frame object.

Integrated hosting, in which we want the content to behave as part of our application, is not supported at all in the system. When Frame navigates to content within the application, we get an odd hybrid of isolated and integrated behavior. Frame isolates its content from its style (and its parent's style), but not from the application's style. Events don't bubble from the content in Frame; however, the objects are accessible from the Content property (meaning that they aren't isolated in a security sense).

For all these reasons, Frame is most useful when we're working with external content, but it can be carefully used for application content.

That's all it has to say -- nothing about property inheritance.

"Windows Presentation Foundation Unleashed says (p. 95):

The Frame control holds arbitrary content, just like all other content controls, but it isolates the content from the rest of the UI. For example, properties that would normally be inherited down the element tree stop when they reach the Frame.

WPF UserControl doesn't inherit parent DataContext

The UserControl is actually inheriting the DataContext from its parent element. There is however no TextFromParent property in that DataContext (because it is the MainWindow instance).

The Binding in the UserControl's XAML is supposed to bind to a property of the UserControl itself, not one of the current DataContext. Hence it must use the UserControl instance as source object:

<TextBlock Text="{Binding TextFromParent,
                  RelativeSource={RelativeSource AncestorType=UserControl}}" />

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Setting the UserControl's DataContext to itself is not an option, because it prevents that a DataContext value is inherited from the parent element of the control.

You may however set the DataContext of the root element in the UserControl's XAML to avoid setting RelativeSource on potentially many Bindings:

<UserControl ...>
    <Grid DataContext="{Binding RelativeSource={RelativeSource AncestorType=UserControl}}">
        <TextBlock Text="{Binding TextFromParent}" />
    </Grid>
</UserControl>

Why does DataContext fail to inherit on objects constructed as attached properties?

Why would it?

Let's remember that FrameworkElement.DataContext is implemented as a DependencyProperty with inheritance flag (see code source here, line 2704) and as such, the "inheritance" of the DataContext you are talking about takes place according to the documented inheritance rules:

Property value inheritance enables child elements in a tree of elements to obtain the value of a particular property from parent elements.

Property value inheritance is particularly about how property values can inherit from one element to another on the basis of the parent-child relationships within a tree of elements

In your case, there is no such parent-child relationship between your TextBlock and its AttachedProperty.FrameworkObject value, not in the WPF sense. The fact that it is an attached or not dependency property doesn't have an impact actually.

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Some comments on your attempts

Creating the object as an element in the Visual Tree successfully binds the value

Yes, because then the object inherits the same DataContext as the TextBlock because they have the same parent in the element tree.

Creating the object within the scope of the TextBlock fails to bind properly

Yes, because the TextBlock is not a parent of the object in the element tree. The TextBlock just happens to hold a reference to that object (I'm hiding the complexity of attached properties here).

Using a data proxy will resolve the binding even when created in a control's scope

Yes, because the object is the child of a ContentControl itself a child of an element with the correct DataContext.

And the most confusing to me. Constructing the FrameworkObject within a ContentControl.Content seems to bind perfectly fine.

Same as above.

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If you really need your object to have a DataContext in your second scenario, you have to set it yourself because it won't be naturally inherited:

<TextBlock x:Name="textBlock" Style="{StaticResource DisplayFromAttached}">
    <local:AttachedProperty.FrameworkObject>
        <local:FrameworkObject DataContext="{Binding ElementName=textBlock, Path=DataContext}" x:Name="CreatedInScope" MyDependencyProperty="{Binding MyProperty, diag:PresentationTraceSources.TraceLevel=High}" />
    </local:AttachedProperty.FrameworkObject>
</TextBlock>

How to use the DataContext of a parent class correctly

The content of the Frame element is not part of visual / logical tree and hence will not persist the data context. You will have to set it explicitly.

    <Frame Source="Page1.xaml" Navigated="Frame_Navigated"/>

    private void Frame_Navigated(object sender, System.Windows.Navigation.NavigationEventArgs e)
    {
        ((FrameworkElement) e.Content).DataContext = this.DataContext;
    }

Hope this helps...

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