CODEWITHSUNDEEP
wpfmvvm
Master
Master

Reputation: 2153

how to set bindings when datacontext is set to ancestor

I'm wondering how do I set the bindings to a public variable within my Viewmodel WorkTabViewModel. I set two examples I tried below,

The Foreground="{Binding MenuItemForeground}" and

Foreground="{Binding MenuItemForeground, RelativeSource={RelativeSource AncestorType=UserControl}}"

But they both don't recognize MenuItemForeground. 

<TextBlock VerticalAlignment="Center" FontWeight="Bold" Margin="1 0 0 0" DataContext="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType=UserControl}}" >
    <TextBlock.ContextMenu>
        <ContextMenu>
            <MenuItem Header="Close tab" cal:Message.Attach="[Click] = [CloseTab()]" />
            <MenuItem Header="Close other tabs" cal:Message.Attach="[Click] = [CloseOtherTabs()]" IsEnabled="False" Foreground="{Binding MenuItemForeground, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
            <MenuItem Header="Close all tabs" cal:Message.Attach="[Click] = [CloseAllTabs()]" IsEnabled="False" Foreground="{Binding MenuItemForeground}"/>
         </ContextMenu>
    </TextBlock.ContextMenu>
</TextBlock>

WorkTabViewModel

public Brush MenuItemForeground { get; set; }
public void CloseTab(){...}
public void CloseOtherTab(){...}
public void CloseAllTabs(){...}

Upvotes: 0

Views: 384

Answers (1)

Lee O.
Lee O.

Reputation: 3312

A context menu is not a part of the visual tree so it's not inheriting the parent controls DataContext. You also can't use the ancestor syntax because of this.

One solution is to use a binding proxy.

public class BindingProxy : Freezable
{
    #region Overrides of Freezable

    protected override Freezable CreateInstanceCore()
    {
        return new BindingProxy();
    }

    #endregion

    public object Data
    {
        get { return (object)GetValue(DataProperty); }
        set { SetValue(DataProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Data.
    // This enables animation, styling, binding, etc...
    public static readonly DependencyProperty DataProperty =
        DependencyProperty.Register("Data",
                                    typeof(object),
                                    typeof(BindingProxy),
                                    new UIPropertyMetadata(null));
}

And it's usage in XAML.

<TextBlock VerticalAlignment="Center" 
           FontWeight="Bold" 
           Margin="1 0 0 0"
           DataContext="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType=UserControl}}">
    <TextBlock.Resources>
        <helper:BindingProxy x:Key="proxy"
                             Data="{Binding }" />
    </TextBlock.Resources>
    <TextBlock.ContextMenu>
        <MenuItem Header="Close tab" 
                  cal:Message.Attach="[Click] = [CloseTab()]" />
        <MenuItem Header="Close other tabs" 
                  cal:Message.Attach="[Click] = [CloseOtherTabs()]"
                  IsEnabled="False"
                  Foreground="{Binding Source={StaticResource proxy}, Data.MenuItemForeground}"/>
        <MenuItem Header="Close all tabs" 
                  cal:Message.Attach="[Click] = [CloseAllTabs()]"
                  IsEnabled="False"
                  Foreground="{Binding Source={StaticResource proxy}, Data.MenuItemForeground}"/>
     </ContextMenu>
</TextBlock.ContextMenu>

Don't forget to declare the helper namespace import at the top of your Window/UserControl.

Upvotes: 1

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