WPF - styling a lookless control: How to access dependecy properties of control from second level of ControlTemplates?

Question

I am extending the ItemsControl (class EnhancedItemsControl : ItemsControl), because I want to add several dependecy properties to it - like AlternativeContent which will be displayed when there are no items in collection (think of 'enter a search terms and hit search' label in a itemscontrol for results of search).

I have subclassed ItemsControl and added an AlternativeContent dep. property of type FrameworkElement to it. Now I want to provide default style in Themes/Generic.xaml (I have added ThemeInfoAttribute to AsseblyInfo, and provided metadata in static costructor as said in this excellent tutorial).

The style contains a ControlTemplate, and I need to use second ControlTemplate inside of ItemsControl template, where I add a ContentPresenter that should show the AlternativeContent.

Now, my problem is how do I tell the ContentPresenter that it should take its content from the top-level EnhancedItemsControl? If I were inside style's ControlTemplate, I would use:

 Content="{Binding AlternativeContent, RelativeSource={RelativeSource TemplatedParent}}" 

but as I am in ItemsControl's ControlTemplate inside style's ControlTemplate, this obviously doesn't work, I'd need to refer not to parent template, but to grandparent template, however, TemplateBinding doesn't have the AncestorLevel parameter.

I also tried:

 Content="{Binding AlternativeContent, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type WPFControls:EnhancedItemsControl}}}"

but that results in empty ContentPresenter as well. I cannot name the TemplatedParent (because it is outside the ControlTemplate), so I cannot refer to it by name. I cannot use TemplatedParent RelativeBinding, because that doesn't reach over two levels of controltemplates. And RelativeSource FindAncestor strangely doesn't work.

Any idea how to solve this? Thank you!

Generic.xaml (excerpt):

 <Style TargetType="{x:Type WPFControls:EnhancedItemsControl}">
  <Setter Property="Template">
   <Setter.Value>
    <ControlTemplate TargetType="{x:Type WPFControls:EnhancedItemsControl}">
     <ItemsControl
      x:Name="RootItemsControl"
      ItemsSource="{Binding}"
      ItemTemplate="{TemplateBinding ItemTemplate}"
      Background="{TemplateBinding Background}"
      HorizontalContentAlignment="Stretch"
      >
      <ItemsControl.Template>
       <ControlTemplate>
        <ScrollViewer
         x:Name="ContentScrollViewer"
         CanContentScroll="False"
         >
         <StackPanel
          x:Name="InnerPanel"
          >

          <ItemsPresenter 
           Width="{Binding ActualWidth, ElementName=InnerPanel}"
           MaxWidth="{Binding ActualWidth, ElementName=InnerPanel}"
           HorizontalAlignment="Stretch"
           />

          <ContentPresenter 
          Content="{Binding AlternativeContent, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type WPFControls:EnhancedItemsControl}}}" 
          >
           <ContentPresenter.Style>
            <Style>
             <Setter Property="ContentPresenter.Visibility" Value="Collapsed" />
             <Style.Triggers>
              <DataTrigger 
              Binding="{Binding Items.Count, ElementName=RootItemsControl}"
              Value="0">
               <Setter Property="ContentPresenter.Visibility" Value="Visible" />
              </DataTrigger>
             </Style.Triggers>
            </Style>
           </ContentPresenter.Style>
          </ContentPresenter>
         </StackPanel>
        </ScrollViewer>
       </ControlTemplate>
      </ItemsControl.Template>
     </ItemsControl>

    </ControlTemplate>
   </Setter.Value>
  </Setter>
 </Style>

Control code:

 public class EnhancedItemsControl : ItemsControl
 {

  static EnhancedItemsControl()
  {
   DefaultStyleKeyProperty.OverrideMetadata(
    typeof(EnhancedItemsControl),
    new FrameworkPropertyMetadata(typeof(EnhancedItemsControl)));
  }


  public FrameworkElement AlternativeContent
  {
   get { return (FrameworkElement)GetValue(AlternativeContentProperty); }
   set { SetValue(AlternativeContentProperty, value); }
  }

  // Using a DependencyProperty as the backing store for AlternativeContent.  This enables animation, styling, binding, etc...
  public static readonly DependencyProperty AlternativeContentProperty =
   DependencyProperty.Register("AlternativeContent", typeof(FrameworkElement), typeof(EnhancedItemsControl), new UIPropertyMetadata(null));

 }

Usage (a List<string> is provided as DataContext):

 <WPFControls:EnhancedItemsControl Height="120" x:Name="EnhancedCollection"
  >
  <WPFControls:EnhancedItemsControl.AlternativeContent>
   <WPFControls:CenteredLabel>
    Alternative content
   </WPFControls:CenteredLabel>
  </WPFControls:EnhancedItemsControl.AlternativeContent>
  <WPFControls:EnhancedItemsControl.ItemTemplate>
   <DataTemplate>
    <TextBlock Text="{Binding}" />
   </DataTemplate>
  </WPFControls:EnhancedItemsControl.ItemTemplate>
 </WPFControls:EnhancedItemsControl>

Answer 1

Oops, my bad,

Content="{Binding AlternativeContent, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type WPFControls:EnhancedItemsControl}}}" 

actually works (but my markup was more complicated than the one in example, and the content was not shown because of other bug...)