XAML Behavior vs. EventTriggerBehavior Action

[limeniye]

States

• Create a simple project with the CommunityToolkit.WinUI.UI.Behaviors
• Add the following code:

public class ShowAttachedFlyoutBehavior
	: BehaviorBase<FrameworkElement>
{
	protected override bool Initialize()
	{
		var result = ShowAttachedFlyout();
		return result;
	}

	protected override bool Uninitialize()
	{
		HideAttachedFlyout();
		return true;
	}

	private bool ShowAttachedFlyout()
	{
		if (AssociatedObject == null)
		{
			return false;
		}
		FlyoutBase.ShowAttachedFlyout(AssociatedObject);
		return true;
	}

	private void HideAttachedFlyout()
	{
		FlyoutBase.GetAttachedFlyout(AssociatedObject).Hide();
	}
}

<Grid x:Name="AddNewGrid" ColumnDefinitions="70,Auto,20" Height="{Binding ElementName=NavigationPanel, Path=ActualHeight}">
	<FlyoutBase.AttachedFlyout>
		<MenuFlyout>
			<MenuFlyoutItem Text="UDP"/>
			<MenuFlyoutItem Text="TCP"/>
		</MenuFlyout>
	</FlyoutBase.AttachedFlyout>
	<i:Interaction.Behaviors>
		<core:EventTriggerBehavior EventName="Tapped" SourceObject="{Binding ElementName=AddNewGrid}">
			<behaviors:ShowAttachedFlyoutBehavior/>
		</core:EventTriggerBehavior>
	</i:Interaction.Behaviors>
	<TextBlock Grid.Column="1" Text="New" VerticalAlignment="Center"/>
</Grid>

• Deploy your application

Expectations

All should be without errors and warnings

Result

Parsing error

Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.dll
The text associated with this error code could not be found.

Option info

If you will remove the line <behaviors:ShowAttachedFlyoutBehavior/> the error will disappear.

Versions of CommunityToolkit.WinUI.UI.Behaviors: 7.1.2
Original post: unoplatform/uno#13145 (comment)
Visual Studio: 17.8.0 Preview 1.0
Repository:
https://github.com/limeniye/UnoCustomBehaviorParsingError

UnoCustomBehaviorParsingError-main.zip

[limeniye]

@michael-hawker it steel doesn't work. The same error message.
Visual Studio 17.9.0 Preview 1.0
.Net 8.0
Uno.WinUI 5.0.**
CommunityToolkit.WinUI.Behaviors 8.0.230907

Maybe I'm doing something wrong?

[michael-hawker]

@limeniye your behavior setup doesn't make sense, I believe that's why you're having an issue. You'd probably get more info if you turned on mixed debugging, maybe?

It looks like you want to trigger an Action in response to the EventTriggerBehavior, so when tapped you open a flyout. For that you don't write a behavior, you use IAction from the XAML Behaviors contracts. That's what allows EventTriggerBehavior to call things in response.

Adding another behavior within there makes no sense. So, what's happening is your behavior is getting initialized right away and trying to open the flyout on load, which I assume is causing some issue within the platform code due to the timing of trying to open a flyout before the components are loaded?

You can look at similar examples of how the Animations system works in the toolkit with the StartAnimationAction.

[limeniye]

@michael-hawker, thank you for the your answer. Indeed, that works!
I apologize for my incompetence.

P.S.

You'd probably get more info if you turned on mixed debugging

I've tried to enable the Common Language Runtime Exceptions but it gives me the same result.

[michael-hawker]

No need to apologize, we're all learning all the time. 😊

If you right-click your project and go to Properties, you can go to the Debug settings here:

You can open the Launch Profiles UI and select Enable native code debugging:

This can sometimes give you different errors (C++/Win32) or details from exceptions that come from within the framework before they get bubbled up.

[limeniye]

@michael-hawker I appreciate your help. Thank you))