WPF ContextMenu woes: How do I set the DataContext of the ContextMenu?

Question

I am having some trouble figuring out how to set the correct DataContext on a ContextMenu.

I have a collection of view models who are the source of an ItemsControl. Each view model has a collection of items which are also the source of another ItemsControl. Each item is used to draw image which has a ContextMenu. The MenuItems in that ContextMenu need to bind to a command on the view model, but the PlacementTarget of the ContextMenu is pointing to the individual item.

My Xaml looks something like this:

<ItemsControl ItemsSource="{Binding Markers"}>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <ItemsControl ItemsSource="{Binding Items}">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <Image>
                            <Image.ContextMenu>
                                <ContextMenu>
                                     <MenuItem Header="Edit" Command="{Binding EditCommand}" />
                                </ContextMenu>
                            </Image.ContextMenu>
                        </Image>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

How can I set the DataContext of the ContextMenu to the item's corresponding parent view model?

Mazur

Answer 1

The ContextMenu is outside of the visual tree. Below is the xaml that should get you the datacontext:

<ItemsControl ItemsSource="{Binding Markers}" Tag="{Binding ElementName=outerControl, Path=DataContext}">
   ...
   <ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
      <MenuItem Header="Edit"
                Command="{Binding EditCommand}" />
   </ContextMenu>
   ...
</ItemsControl>

This post explains how this works.

Weinhardt

The problem with this is I do not want to bind to what the PlacementTarget is. I want to bind to the DataContext of the outer control. – Mazur

Are you sure they don't have the same DataContext (ie outerControl and inner itemsControl)? – Weinhardt

Yes, the DataContext I get using PlacementTarget is a level too deep. I get back the an item, but what I need is the view model that has the collection that contains that item. If I could bind to the DataContext of the outer control, that would be perfect. – Mazur

I guess it would be, I need the DataContext of the Inner ItemsControl, but that is the DataContext of the outer control to the Image. – Mazur

I have gotten around this by storing the outercontrol's datacontext in the Tag property of the innercontrol. This should allow you to use the PlacementTarget.Tag. – Weinhardt

it's not the most elegant thing, but using Tag works :) If you could update your answer, I'll mark this as correct. – Mazur

Yeah, my thoughts exactly, but that's the best I've been able to do. – Weinhardt

Be careful! Don't put Mode=OneTimeon the ContextMenu's DataContext value as I did. This will cause the bindings to fail for some reason. – Reinstate

Answer 2

You can use a markupextension:

using System;
using System.Windows.Controls;
using System.Windows.Markup;
using System.Xaml;

[MarkupExtensionReturnType(typeof(ContentControl))]
public class RootObject : MarkupExtension
{
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var rootObjectProvider = (IRootObjectProvider)serviceProvider.GetService(typeof(IRootObjectProvider));
        return rootObjectProvider?.RootObject;
    }
}

It lets you do:

<ItemsControl ItemsSource="{Binding Markers}">
   ...
   <ContextMenu DataContext="{Binding DataContext, Source={local:RootObject}}">
      <MenuItem Header="Edit"
                Command="{Binding EditCommand}" />
   </ContextMenu>
   ...
</ItemsControl>

Matrimony

Nice idea, but maybe this only works for menus within an ItemsControl? I could not get it working in a ContentPresenter for example. – Hobbs

This worked for me whereas lots didn't. Thanks. 👍 – Eadie

Answer 3

I don't like use Tag. I prefer attached property.

You need add attached property:

public static readonly DependencyProperty DataContextExProperty =
   DependencyProperty.RegisterAttached("DataContextEx",
                                       typeof(Object), 
                                       typeof(DependencyObjectAttached));

public static Object GetDataContextEx(DependencyObject element)
{
    return element.GetValue(DataContextExProperty);
}

public static void SetDataContextEx(DependencyObject element, Object value)
{
    element.SetValue(DataContextExProperty, value);
}

In XAML:

<Button attached:DependencyObjectAttached.DataContextEx="{Binding ElementName=MyDataContextElement, Path=DataContext}">
    <Button.ContextMenu>
        <ContextMenu DataContext="{Binding RelativeSource={RelativeSource Self}, Path=PlacementTarget.(attached:DependencyObjectAttached.DataContextEx)}">
        </ContextMenu>
    </Button.ContextMenu>
</Button>

Jehu

Answer 4

This code allows you to use both the global and local DataContext (of entire userControl and of current TreeViewItem):

<TreeView Grid.Row="0" ItemsSource="{Binding Path=SelectableEnterprises}">
<TreeView.ItemTemplate>
    <HierarchicalDataTemplate ItemsSource="{Binding Children}">
        <Grid Height="20" Tag="{Binding DataContext, ElementName=userControl}">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="25"/>
                <ColumnDefinition/>
            </Grid.ColumnDefinitions>
            <Grid.ContextMenu>
                <ContextMenu DataContext="{Binding PlacementTarget, RelativeSource={RelativeSource Self}}" >
                    <ContextMenu.Visibility>
                        <MultiBinding Converter="{converters:SurveyReportVisibilityConverter}">
                            <Binding Path="DataContext"/> <!--local DataContext-->
                            <Binding Path="Tag.SelectedSurvey"/> <!--global DataContext-->
                        </MultiBinding>
                    </ContextMenu.Visibility>

                    <MenuItem Header="Show HTML-report" Command ="{Binding Tag.OpenHTMLReportCommand}" 
                              CommandParameter="{Binding DataContext}" />
                </ContextMenu>
            </Grid.ContextMenu>

Reticule