Shapes without handlers shouldn't be added as LogicalChildren

[drasticactions]

Description

It is always null when calling for the Handler on a Maui shape. This matters as tooling such as XAML Hot Reload and the Live Visual Tree attempt to draw borders around elements when you hover over them in the menus. If an MAUI Shape appears in the list, we will try and render a border around it. That will fail, since the handler is null, and it will throw an exception above, crashing the app.

That can be worked around in XAML Hot Reload, but we should see why it's null here too. It's broken in both net7.0 and net8.0, and on all platforms.

Steps to Reproduce

1. Create a Shape (such as a border shape)
2. Try and reference the handler

It will be null.

Link to public reproduction project repository

https://github.com/drasticactions/MauiRepros/tree/main/MauiShapeNet7

Version with bug

7.0.92

Is this a regression from previous behavior?

No, this is something new

Last version that worked well

Unknown/Other

Affected platforms

iOS, Android, Windows, macOS

Affected platform versions

No response

Did you find any workaround?

No response

Relevant log output

No response

[ghost]

We've added this issue to our backlog, and we will work to address it as time and resources allow. If you have any additional information or questions about this issue, please leave a comment. For additional info about issue management, please read our Triage Process.

[XamlTest]

Verified this on Visual Studio Enterprise 17.8.0 Preview 1.0. Repro on Windows 11 .NET 8, Android 13.0-API33 and iOS 16.4 with below Project:
MauiShape.zip

After clicking the button, it will show "Border Shape Null"

[chabiss]

@samhouts This bug blocks https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1911092, which is a severe regression to .NET 7.

[drasticactions]

With some more testing: Shapes alone rendered on screen do appear to have handlers correctly attached after they are handled. For Borders specifically, StrokeShapes (which are rendered on screen) do not have handlers.

[hansmbakker]

I see that this issue is fixed now. I haven't been able to test it yet, but will a Border now show up its outline in Xaml Live Preview or not?

From the description saying "ignore elements with null handlers" it sounds as if it will be ignored (as a workaround) rather than the Border element having a correct implementation that provides the right info to Xaml Live Preview?

If so, is there an issue tracking this?
If not, apologies for misunderstanding.

[drasticactions]

Short answer: Yes*

Long Answer: Borders could always be drawn (as they were with net7.0), the issue was with Border StrokeShapes. They not "technically" shapes, but are used as to define how the border should be drawn. This is inconsistent with general UI elements, which have handlers that should never be null, and since StrokeShape is a UI Element, it was added to LogicalChildren with net8.0, which was then breaking the XAML Live Preview Adorner layer, since UI Elements once rendered should never have null handlers.

#3558

This issue is tracking a change of it from Shape to Geometry, but it's a big API shift.

With net8.0, those StrokeShapes (Or any element that doesn't have a handler, which so far I believe this is the only one) are removed from the Visual Tree list, so now if you have any border with a StrokeShape, it won't break the visual tree adorner layer.

*There may be cases where it doesn't work that we don't know of, since it can be used on a huge amount of controls, you could find a case where it does not work, in which case, file a bug.