After migrating to VB.NET Core 9.0 from 8.0, I am getting error messages on menu bindings

Question

After migrating from version 8.0 to version 9.0, I am getting error messages related to the binding of menu items. I am working with Visual Studio 17.12.3 and .NET Core 9.0.101 on a Windows 11 (23H2) machine. Further down in the XAML code, I have the same binding in a button, which does not generate any errors. The XAML code is from a WPF project built using MVVM, with no code-behind. When I revert to version 8.0, everything works fine again. Is something changed for the menuitems?

The ERROR is: System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=DataContext.BttnLeeg; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand')

The code that works (RelativeSource Binding of the Button):

 <Button  Height="18" Width="18" HorizontalAlignment="Right" 
                             ToolTip="{Binding DataContext.BttnRemoveConnection_ToolTip, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
                             Command="{Binding DataContext.BttnRemoveConnection,         RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"  
                             CommandParameter="{Binding RetourValue}"
                             Visibility="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.ShowBttn}">
     <DockPanel          LastChildFill="True" Width="18" Height="18">
         <TextBlock      Text="{Binding DataContext.BttnRemoveConnection_Content, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"      Style="{StaticResource RemoveLink_Background}" Margin="0,0,0,0"  />
         <TextBlock      Text="{Binding DataContext.BttnRemoveConnection_Content_Info, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" Style="{StaticResource RemoveLink_Foreground}" Margin="-16,-4,0,0"  />
     </DockPanel>
 </Button>

The code with the ERROR (just one menu item, of the 5 in the original code):

 <UserControl.Resources>
     <ContextMenu x:Key="MyContextMenu" x:Shared ="true" Background="DarkGray" Foreground="Black" >
         <MenuItem Header="Leeg" Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.BttnLeeg}" CommandParameter="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType=ContextMenu}}" Height="24" />
     </ContextMenu>
 </UserControl.Resources>

Answer 1

Hi,@Mike van der Waard. Welcome to Microsoft Q&A. 

You could refer to the following method to fix your problem.

When the resources defined in Resources need to be bound to DataContext, define DataContext in Resources for other controls to perform data binding.

Reference code:

<UserControl.Resources>
    <local:UserControl1ViewModel x:Key="UserControl1ViewModelInResource"> </local:UserControl1ViewModel>
        <ContextMenu x:Key="MyContextMenu" x:Shared ="true" Background="DarkGray" Foreground="Black" DataContext="{StaticResource UserControl1ViewModelInResource}">
            <MenuItem Header="Leeg" Command="{Binding BttnLeeg}" CommandParameter="{Binding Path=PlacementTarget, RelativeSource={RelativeSource AncestorType=ContextMenu}}" Height="24" />
        </ContextMenu>
</UserControl.Resources>

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