ContextMenu.ItemsSource binding acts as OneTime even if specified otherwise

[derekantrican]

Describe the bug

I have bound a ContextMenu.ItemsSource property to a list in my viewmodel, but the getter is only called once, even if I specify a different binding mode such as OneWay or TwoWay, the bindind still acts as OneTime

To Reproduce

MainWindow.axaml:

<Button>
  <Button.ContextMenu>
    <ContextMenu ItemsSource="{Binding Items, Mode=TwoWay}">
      <ContextMenu.Styles>
        <Style Selector="MenuItem">
          <Setter Property="Header" Value="{Binding .}"/>
        </Style>
      </ContextMenu.Styles>
  </Button.ContextMenu>
</Button>

MainViewModel.cs:

public ObservableCollection<string> Items
{
  get
  { // <---- Placing breakpoint here
    return new ObservableCollection<string>(new List<string> { "Item1", "Item2", "Item3" });
  }
}

Expected behavior

I would expect the getter for Items to be called every time the context menu is opened, but it is not

Avalonia version

11.1.0

OS

Windows

Additional context

No response

[anovik]

Found related problem: it seems the properties like IsVisible or IsEnabled also has only one-time binding for ContextMenu/MenuItem which is odd.

Temporarily I solved that by switching from ContextMenu to MenuFlyout, binding there works correctly. But still, there is a problem with ContextMenu.

[derekantrican]

@anovik I'm not seeing correct bindings, even with MenuFlyout - the getter is still only called once at the beginning. Can you share your snippet?

Here's what I tried changing mine to:

<Button>
	<Button.ContextFlyout>
		<MenuFlyout ItemsSource="{Binding Items, Mode=TwoWay}"><!--I tried multiple "Modes" here-->
			<MenuItem Header="{Binding Header}" Command="{Binding ActionCommand}"/>
		</MenuFlyout>
	</Button.ContextFlyout>
</Button>

[derekantrican]

Ok, ChatGPT to the rescue. I added AttachedToVisualTree="ContextMenu_AttachedToVisualTree" to my ContextMenu and in the code-behind, simply called my "LoadMenuItems" command:

private void ContextMenu_AttachedToVisualTree(object sender, VisualTreeAttachmentEventArgs e)
{
	mainViewModel.ContextMenuItems.Clear();

        foreach (.....)
	{
		mainViewModel.ContextMenuItems.Add(.....);
	}
}

And that seems to dynamically work for updating the items every time. Definitely a workaround - wish I didn't have to use the code-behind for this

[maxkatz6]

"OneWay" doesn't mean that it will be called each time control is displayed.
"OneWay" means value will be updated each time (view) model notifies about changes.