Outside Property inside a DataTemplate WPF - wpf

Question

Scenario: I have a ListBox and the ListBoxItems have a DataTemplate. What I want to do is put a ContextMenu in the DataTemplate. The catch is that I want this ContextMenu ItemsSource to be different depending on certain properties in the window. My initial thought is that I could just bind the ItemsSource to a Property in the window and that would return an ItemsSource; however, I cant seem to bind to this property correctly. I believe this is because I am in the DataTemplate and consequently the DataContext (I believe that is the right word) is of that ListBoxItem and not of the window.
How could I get the ContextMenu that is inside a DataTemplate to bind to a Property outside of the DataTemplate.

Answer 1

You can get the DataContext from your window by using the RelativeSource FindAncestor syntax
<DataTemplate>
<TextBlock Text="{Binding MyInfo}">
<TextBlock.ContextMenu>
<Menu ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.MyContextMenuItems}"/>
</TextBlock.ContextMenu>
</TextBlock>
</DataTemplate>
Not totally sure, but the binding is correct...
If your DataContext is on another object type, you just have to change the AncestorType (eg. by UserControl).

Answer 2

This might be a good candidate for an AttachedProperty. Basically what you would do is wrap your ContextMenu in a UserControl and then add a Dependency Property to the UserControl. For example:
MyContextMenu.xaml
<UserControl x:Class="MyContextMenu" ...>
<UserControl.Template>
<ContextMenu ItemSource="{Binding}" />
</UserControl.Template>
</UserControl>
MyContextMenu.xaml.cs
public static readonly DependencyProperty MenuItemsSourceProperty = DependencyProperty.RegisterAttached(
"MenuItemsSource",
typeof(Object),
typeof(MyContextMenu),
new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender)
);
public static void SetMenuItemsSource(UIElement element, Boolean value)
{
element.SetValue(MenuItemsSourceProperty, value);
// assuming you want to change the context menu when the mouse is over an element.
// use can use other events. ie right mouse button down if its a right click menu.
// you may see a perf hit as your changing the datacontext on every mousenter.
element.MouseEnter += (s, e) => {
// find your ContextMenu and set the DataContext to value
var window = element.GetRoot();
var menu = window.GetVisuals().OfType<MyContextMenu>().FirstOrDefault();
if (menu != null)
menu.DataContext = value;
}
}
public static Object GetMenuItemsSource(UIElement element)
{
return element.GetValue(MenuItemsSourceProperty);
}
Window1.xaml
<Window ...>
<Window.Resources>
<DataTemplate TargetType="ListViewItem">
<Border MyContextMenu.MenuItemsSource="{Binding Orders}">
<!-- Others -->
<Border>
</DataTemplate>
</Window.Resources>
<local:MyContextMenu />
<Button MyContextMenu.MenuItemsSource="{StaticResource buttonItems}" />
<ListView ... />
</Window>
VisualTreeHelpers
public static IEnumerable<DependencyObject> GetVisuals(this DependencyObject root)
{
int count = VisualTreeHelper.GetChildrenCount(root);
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(root, i);
yield return child;
foreach (var descendants in child.GetVisuals())
{
yield return descendants;
}
}
}
public static DependencyObject GetRoot(this DependencyObject child)
{
var parent = VisualTreeHelper.GetParent(child)
if (parent == null)
return child;
return parent.GetRoot();
}
This example is un-tested I'll take a look later tonight and make sure its accurate.