ElementName Binding from MenuItem in ContextMenu

Question

Has anybody else noticed that Bindings with ElementName do not resolve correctly for MenuItem objects that are contained within ContextMenu objects? Check out this sample:

<Window x:Class="EmptyWPF.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300"
    x:Name="window">
    <Grid x:Name="grid" Background="Wheat">
     <Grid.ContextMenu>
      <ContextMenu x:Name="menu">
       <MenuItem x:Name="menuItem" Header="Window" Tag="{Binding ElementName=window}" Click="MenuItem_Click"/>
       <MenuItem Header="Grid" Tag="{Binding ElementName=grid}" Click="MenuItem_Click"/>
       <MenuItem Header="Menu" Tag="{Binding ElementName=menu}" Click="MenuItem_Click"/>
       <MenuItem Header="Menu Item" Tag="{Binding ElementName=menuItem}" Click="MenuItem_Click"/>
      </ContextMenu>
     </Grid.ContextMenu>
     <Button Content="Menu" 
       HorizontalAlignment="Center" VerticalAlignment="Center" 
       Click="MenuItem_Click" Tag="{Binding ElementName=menu}"/>
     <Menu HorizontalAlignment="Center" VerticalAlignment="Bottom">
      <MenuItem x:Name="anotherMenuItem" Header="Window" Tag="{Binding ElementName=window}" Click="MenuItem_Click"/>
      <MenuItem Header="Grid" Tag="{Binding ElementName=grid}" Click="MenuItem_Click"/>
      <MenuItem Header="Menu" Tag="{Binding ElementName=menu}" Click="MenuItem_Click"/>
      <MenuItem Header="Menu Item" Tag="{Binding ElementName=anotherMenuItem}" Click="MenuItem_Click"/>
     </Menu>
    </Grid>
</Window>

All of the bindings work great except for the bindings contained within the ContextMenu. They print an error to the Output window during runtime.

Any one know of any work arounds? What's going on here?

Answer 1

After experimenting a bit, I discovered one work around:

Make top level Window/UserControl implement INameScope and set NameScope of ContextMenu to the top level control.

public class Window1 : Window, INameScope
{
    public Window1()
    {
        InitializeComponent();
        NameScope.SetNameScope(contextMenu, this);
    }

    // Event handlers and etc...

    // Implement INameScope similar to this:
    #region INameScope Members

    Dictionary<string, object> items = new Dictionary<string, object>();

    object INameScope.FindName(string name)
    {
        return items[name];
    }

    void INameScope.RegisterName(string name, object scopedElement)
    {
        items.Add(name, scopedElement);
    }

    void INameScope.UnregisterName(string name)
    {
        items.Remove(name);
    }

    #endregion
}

This allows the context menu to find named items inside of the Window. Any other options?

Answer 2

Context menus are tricky to bind against. They exist outside the visual tree of your control, hence they can't find your element name.

Try setting the datacontext of your context menu to its placement target. You have to use RelativeSource.

<ContextMenu DataContext="{Binding PlacementTarget, RelativeSource={RelativeSource Self}}"> ...

Answer 3

I found a much simpler solution.

In the code behind for the UserControl:

NameScope.SetNameScope(contextMenu, NameScope.GetNameScope(this));