How can I access the root DataContext in a DataTemplate in WPF?

Question

I have a grid of items which is populated using databinding. In the grid I have a DataTemplate for certain cells. I need to access the DataContext of the root element (the one which is hosting the grid) so that I can access additional bindings to support my datatemplate.

So you have:

Window
    Window.DataContext = TheDataSourceWithItemsAndSupports
    DataGrid.ItemsSource = {Binding Items}
        DataTemplate
            ListBox.ItemsSource = {Binding Supports}

I want the {Binding Supports} on TheDataSourceWithItemsAndSupports, but I don't see how to do that. I tried specifying {Binding} but that always returns null. I also tried using RelativeSource FindAncestor, but that yields null too.

Any clues?

Answer 1

Maybe try

Window Name="TheWindow"
...
ListBox.ItemsSource = {Binding DataContext.Supports, ElementName=TheWindow}

Answer 2

Another little trick to bind to your root context

<ListBox ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}, AncestorLevel=1}, Path=DataContext.Supports}"/>