Binding to property in owning window's viewmodel within a DataTemplate in Window.Resources

Question

I have a DataTemplate within my Window's Resources section that creates a TextBlock with a ContextMenu. I want to be able to set whether a MenuItem within the ContextMenu is visible from within my Window's view model. I have tried accessing the DataContext of the Window by setting ElementName, and also tried setting RelativeSource, but both approaches resulted in binding errors. I'm not sure what else I can try.

I have created a small example that shows what I'm trying to do:

XAML:

<Window x:Class="DataTemplateTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">


<Window.Resources>
    <ResourceDictionary>
        <DataTemplate x:Key="TestDataTemplate">
            <TextBlock Text="{Binding}">
                <TextBlock.ContextMenu>
                    <ContextMenu>
                        <MenuItem Header="Test" Visibility="{Binding Path=DataContext.MenuItemVisible, ElementName=Root}"/>
                    </ContextMenu>
                </TextBlock.ContextMenu>
            </TextBlock>
        </DataTemplate>
    </ResourceDictionary>
</Window.Resources>

<ScrollViewer x:Name="Root">
    <ItemsControl ItemsSource="{Binding Path=Items}" ItemTemplate="{StaticResource TestDataTemplate}" />
</ScrollViewer>

Code behind:

using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;

namespace DataTemplateTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        protected readonly MainWindowViewModel vm;

        public MainWindow()
        {
            InitializeComponent();
            vm = new MainWindowViewModel();
            DataContext = vm;
        }
    }

    public class MainWindowViewModel : INotifyPropertyChanged
    {
        private Visibility menuItemVisible = Visibility.Hidden;
        public Visibility MenuItemVisible { get { return menuItemVisible; } set { menuItemVisible = value; NotifyPropertyChanged("MenuItemVisible"); } }

        public List<string> Items { get; set; }

        public MainWindowViewModel()
        {
            Items = new List<string>() { "Alpha", "Beta", "Gamma" };
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

The error I get is

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=Root'. BindingExpression:Path=DataContext.MenuItemVisible; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Visibility' (type 'Visibility')

When I set RelativeSource instead of ElementName in the binding:

RelativeSource={RelativeSource Mode=FindAncestor, 
                AncestorType={x:Type ScrollViewer}}

I get the following error:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.ScrollViewer', AncestorLevel='1''. BindingExpression:Path=DataContext.MenuItemVisible; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Visibility' (type 'Visibility')

Answer 1

I have found the answer here:

So all I had to do to access the window's DataContext was set:

Source={x:Reference Name=Root}

An explanation of why ElementName does not work in this case is found here. Specifically:

Probably the simplest example of where we don't have inheritance context links is across > random property elements:

<Button>
  <Button.ContextMenu>
    <ContextMenu/>
  </Button.ContextMenu>
</Button>

ContextMenu is neither a visual nor logical child of Button, nor is it one of the inheritance context cases listed above (ContextMenu is not a Freezable).