WPF returns UnsetValue on RelativeSource to Ancestor

Question

I was able to create a neat context menu that controls visibility of columns and wanted to show values of hidden ones in a tooltip, but I'm unable to, because somehow the very same binding is returning DependencyProperty.UnsetValue. Why? What makes the difference and how to fix that?

 <telerik:RadGridView x:Name="radVideosGridView" ItemsSource="{Binding Customers}"> <telerik:RadGridView.RowStyle> <Style TargetType="telerik:GridViewRow"> <Setter Property="ToolTip"> <Setter.Value> <StackPanel Orientation="Horizontal"> <TextBlock> <TextBlock.Text> <MultiBinding Converter="{StaticResource HiddenColumnsToTooltipConverter}" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="False"> <Binding Path="PersonalData" /> <!-- Passes {{DependencyProperty.UnsetValue}} --> <Binding Path="Columns" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type telerik:RadGridView}}}" /> </MultiBinding> </TextBlock.Text> </TextBlock> </StackPanel> </Setter.Value> </Setter> </Style> </telerik:RadGridView.RowStyle> <telerik:RadGridView.Columns> <telerik:GridViewDataColumn DataMemberBinding="{Binding PersonalData.FirstName}" Header="Last Name"/> <telerik:GridViewDataColumn DataMemberBinding="{Binding PersonalData.SecondName}" Header="Second Name" IsVisible="False"/> <telerik:GridViewDataColumn DataMemberBinding="{Binding PersonalData.LastName}" Header="Last Name"/> </telerik:RadGridView.Columns> <!-- Works fine --> <telerik:RadContextMenu.ContextMenu> <telerik:RadContextMenu> <telerik:RadContextMenu.Template> <ControlTemplate> <Grid> <telerik:RadListBox ItemsSource="{Binding Columns, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type telerik:RadGridView}}}"> <telerik:RadListBox.ItemTemplate> <DataTemplate> <CheckBox Content="{Binding Header}" IsChecked="{Binding IsVisible, Mode=TwoWay}" /> </DataTemplate> </telerik:RadListBox.ItemTemplate> </telerik:RadListBox> </Grid> </ControlTemplate> </telerik:RadContextMenu.Template> </telerik:RadContextMenu> </telerik:RadContextMenu.ContextMenu> </telerik:RadGridView>

KwarcPL · Accepted Answer · 2025-11-25 12:41:29Z

I've found out the reason behind difference in behavior. RadContextMenu is a child of RadGridView while ToolTip is in a different branch build around PopUp primite so we access columns by Ancestor source. I've write a work-around based on this code:

https://stackoverflow.com/a/1759923

public class HiddenColumnsToTooltipConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, CultureInfo culture) { if (value != null && value is Camera camera) { try { var window = Application.Current.Windows.OfType<Window>().SingleOrDefault(x => x.IsActive); var columns = ((RadGridView)FindChild(window, $"{parameter}", typeof(RadGridView))).Columns; ... return result; } catch { } } return "Nothing to show"; } public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) { return Binding.DoNothing; } public static DependencyObject FindChild(DependencyObject reference, string childName, Type childType) { DependencyObject foundChild = null; if (reference != null) { int childrenCount = VisualTreeHelper.GetChildrenCount(reference); for (int i = 0; i < childrenCount; i++) { var child = VisualTreeHelper.GetChild(reference, i); if (child.GetType() != childType) { foundChild = FindChild(child, childName, childType); if (foundChild != null) break; } else if (!string.IsNullOrEmpty(childName)) { var frameworkElement = child as FrameworkElement; if (frameworkElement != null && frameworkElement.Name == childName) { foundChild = child; break; } } else { foundChild = child; break; } } } return foundChild; }

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