在设计时和运行时绑定到嵌套UserControl的父级

Question

I am working with a custom window class that adds some behaviours to the window:

class CustomWindow : Window {
    public CustomWindow() {
        // ...
    }
}

My current MainWindow.xaml looks as expected:

<local:CustomWindow ...>
    <!-- ... -->
</local:CustomWindow>

Now I wanted to host the content of the window in a custom container which should be the root element of the window itself but I struggled to implement the automatic creation of the container in the first place. Thus I am doing manually what I wanted to automate now with a "hardcoded" control:

<local:CustomWindow ...>
    <local:CustomUserControl>
        <!-- ... -->
    </local:CustomUserControl>
</local:CustomWindow>

In order to display the content that has been added via XAML I have introduced a Content property like this:

[ContentProperty("InnerContent")]
public partial class CustomUserControl : UserControl
{
    public static readonly DependencyProperty InnerContentProperty =
        DependencyProperty.Register("InnerContent", typeof(object), 
                                    typeof(CustomUserControl));

    public object InnerContent
    {
        get => GetValue(InnerContentProperty);
        set => SetValue(InnerContentProperty, value);
    }
}

And a ContentPresenter in the XAML file with Content="{Binding Path=InnerContent, ElementName=customUserControl}" . At this point I am struggling with some further bindings I want to achieve. I have a TextBlock I want to bind to a property of the parent window now. The hierarchy looks as follows:

CustomWindow
|- CustomUserControl
   |- ...
      |- TextBlock

When I set the Text property to {Binding Path=Title, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:CustomWindow}}} this works during runtime of course but not during design-time in the window designer. And of course I cannot use this binding with a design DataContext that I have introduced like this d:DataContext="{d:DesignInstance local:FakeCustomUserControlData, IsDesignTimeCreatable=True}" .

At this point I have two questions:

1. Is it possible to have design-time data in the CustomUserControl.xaml designer, while in the MainWindow.xaml designer and during runtime I get the real data about the parent? (I noticed during testing that the Parent property of the CustomUserControl is null during its constructor so I wasn't able to obtain the data of a parent window if there exists one.)
2. Is there actually a way to "inject" the CustomUserControl into the window without manually having to add it to the window? I tried to replace the Content property in the CustomWindow constructor but it got replaced during some point and was never visible.

Answer 1

Is there actually a way to "inject" the CustomUserControl into the window without manually having to add it to the window?

Define a custom template for the window that includes your UserControl :

<Window x:Class="WpfApp1.Window1"
        ...>
    <Window.Template>
        <ControlTemplate TargetType="Window">
            <AdornerDecorator>
                <local:CustomUserControl Background="White">
                    <ContentPresenter />
                </local:CustomUserControl>
            </AdornerDecorator>
        </ControlTemplate>
    </Window.Template>
    <Grid>
        <TextBlock>the content...</TextBlock>
    </Grid>
</Window>

Is it possible to have design-time data in the CustomUserControl.xaml designer, while in the MainWindow.xaml designer and during runtime I get the real data about the parent?

You should be able to set a design time data context for the UserControl : WPF data context for design time and run time .