title: How can I access the root DataContext in a DataTemplate in WPF?
body: <p>I have a grid of items which is populated using databinding.
  In the grid I have a <code>DataTemplate</code> for certain cells. I need to access the <code>DataContext</code> of the root element (the one which is hosting the grid) so that I can access additional bindings to support my datatemplate.</p>
  
  <p>So you have:</p>
  
  <pre><code>Window
      Window.DataContext = TheDataSourceWithItemsAndSupports
      DataGrid.ItemsSource = {Binding Items}
          DataTemplate
              ListBox.ItemsSource = {Binding Supports}
  </code></pre>
  
  <p>I want the <code>{Binding Supports}</code> on <code>TheDataSourceWithItemsAndSupports</code>, but I don't see how to do that. I tried specifying <code>{Binding}</code> but that always returns <code>null</code>. I also tried using <code>RelativeSource FindAncestor</code>, but that yields <code>null</code> too.</p>
  
  <p>Any clues?</p>