Xaml Namescope and Template Question Concerning WPF ContextMenu

Question

Everything in the code below works except for the binding on the ContextMenu. This is evidently due to the fact that the ContextMenu is located inside of a Style, which puts it in a different namescope from the rest of the xaml. I am looking for a solution where I won't have to instantiate a ContextMenu in the code-behind, since the application where I have to apply the solution contains a very large ContextMenu with a lot of bindings. There must be a way to accomplish this in xaml, otherwise it would seem like a serious oversight. Also note that I've already tried traversing the element tree using VisualTreeHelper and LogicalTreeHelper, but I wasn't able to find the ContextMenu from the root element of the Window (these classes evidently skipped over the interesting elements). Anyway, all of the code is below. This can be pasted into a new WPF application in Visual Studio, and nothing is missing.

Here's the code for App.xaml.cs (the xaml was left unchanged):

using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            WindowV windowV = new WindowV();
            WindowVM windowVM = new WindowVM();

            windowV.DataContext = windowVM;

            windowV.Show();
        }
    }
}

Here's the xaml for what was originally Window1:

<Window x:Class="WpfApplication1.WindowV"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:src="clr-namespace:WpfApplication1"
        Name="MainWindow"
        Title="WindowV" Height="300" Width="300">
    <Window.Resources>
        <Style TargetType="{x:Type ItemsControl}">
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsLocked}" Value="true">
                    <Setter Property="ItemsSource" Value="{Binding LockedList}" />
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <TextBlock Text="{Binding}" />
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding IsLocked}" Value="false">
                    <Setter Property="ItemsSource" Value="{Binding RegularList}" />
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <TextBlock Text="{Binding}">
                                    <TextBlock.ContextMenu>
                                        <ContextMenu>
                                            <MenuItem Header="{Binding MenuItem1, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />
                                            <MenuItem Header="{Binding MenuItem2, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />
                                            <MenuItem Header="{Binding MenuItem3, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />
                                        </ContextMenu>
                                    </TextBlock.ContextMenu>
                                </TextBlock>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="4*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <ItemsControl Grid.Row="0" />
        <Button Name="ToggleButton"
                Grid.Row="1"
                Content="Toggle Lock"
                Click="OnToggleLock" />
    </Grid>
</Window>

Here's the codebehind for what was originally Window1:

using System.Windows;
using System.Windows.Markup;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class WindowV : Window
    {
        public WindowV()
        {
            InitializeComponent();
        }

        private void OnToggleLock(object sender, RoutedEventArgs e)
        {
            if (((WindowVM)(DataContext)).IsLocked == true)
                ((WindowVM)(DataContext)).IsLocked = false;
            else
                ((WindowVM)(DataContext)).IsLocked = true;
        }
    }
}

A new class was added to the project called WindowVM. Here's its code:

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

namespace WpfApplication1
{
    public class WindowVM : INotifyPropertyChanged
    {
        public string MenuItem1
        {
            get
            {
                string str = "Menu item 1";
                return str;
            }
        }
        public string MenuItem2
        {
            get
            {
                string str = "Menu item 2";
                return str;
            }
        }
        public string MenuItem3
        {
            get
            {
                string str = "Menu item 3";
                return str;
            }
        }

        public List<string> LockedList
        {
            get
            {
                List<string> list = new List<string>();
                list.Add("This items control is currently locked.");
                return list;
            }
        }
        public List<string> RegularList
        {
            get
            {
                List<string> list = new List<string>();
                list.Add("Item number 1.");
                list.Add("Item number 2.");
                list.Add("Item number 3.");
                return list;
            }
        }

        private bool _isLocked;
        public bool IsLocked
        {
            get { return _isLocked; }
            set
            {
                if (_isLocked != value)
                {
                    _isLocked = value;
                    OnPropertyChanged("IsLocked");
                }
            }
        }

        public WindowVM()
        {
            IsLocked = false;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string PropertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
        }
    }
}

Any insight would be very appreciated. Thanks much!

Andrew

Answer 1

Okay - I am having a little trouble following what you are trying to accomplish - but try the following:

<ContextMenu>
     <MenuItem Header="{Binding DataContext.MenuItem1, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />
     ...

And to make your code easier, you can then try:

<ContextMenu DataContext="{Binding DataContext, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}">
     <MenuItem Header="{Binding MenuItem1}"/>
     ...

Problem was that you were binding to the UI element Window which does not have a property called MenuItem1 etc. The DataContext property has the data you are interested in.

Answer 2

Alright, this solution works: I changed the WindowV.xaml and WindowV.xaml.cs files as follows. The following corrections fix the problem concerning namescope in xaml.

Here's the new WindowV.xaml file:

<Window x:Class="WpfApplication1.WindowV"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:src="clr-namespace:WpfApplication1"
        Name="RootElement"
        Title="WindowV" Height="300" Width="300">
    <Window.Resources>
        <ContextMenu x:Key="myContextMenu" DataContext="{Binding Path=DataContext, ElementName=RootElement}">
            <MenuItem Header="{Binding MenuItem1}" />
            <MenuItem Header="{Binding MenuItem2}" />
            <MenuItem Header="{Binding MenuItem3}" />
        </ContextMenu>
        <Style TargetType="{x:Type ItemsControl}">
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsLocked}" Value="true">
                    <Setter Property="ItemsSource" Value="{Binding LockedList}" />
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <TextBlock Text="{Binding}" />
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding IsLocked}" Value="false">
                    <Setter Property="ItemsSource" Value="{Binding RegularList}" />
                    <Setter Property="ItemTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <TextBlock Text="{Binding}" ContextMenu="{StaticResource myContextMenu}" />
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="4*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <ItemsControl Grid.Row="0" />
        <Button Name="ToggleButton"
                Grid.Row="1"
                Content="Toggle Lock"
                Click="OnToggleLock" />
    </Grid>
</Window>

Here's the corresponding code-behind:

using System.Windows;
using System.Windows.Markup;
using System;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class WindowV : Window
    {
        public WindowV()
        {
            InitializeComponent();

            System.Windows.Controls.ContextMenu contextMenu =
                FindResource("myContextMenu") as System.Windows.Controls.ContextMenu;

            NameScope.SetNameScope(contextMenu, NameScope.GetNameScope(this as DependencyObject));
            contextMenu.RegisterName("RootElement", this);
        }

        private void OnToggleLock(object sender, RoutedEventArgs e)
        {
            if (((WindowVM)(DataContext)).IsLocked == true)
                ((WindowVM)(DataContext)).IsLocked = false;
            else
                ((WindowVM)(DataContext)).IsLocked = true;
        }
    }
}

Andrew