CollectionView DataTemplate with Switch: Toggled event is called in infinite loop causing app to crash.

[pme442]

Description

I am creating this issue in regard to an existing issue that has recently been closed but NOT fixed. #29556 (comment)
As you can see, it has also been verified by two other people.
I have upgraded to the latest version (9.0.110 SR11) but the issue is still present.
I am unable to release my app to production until this is fixed.

Steps to Reproduce

In the Collection Views tab -> select the 2nd category (Favorites) -> find the switch question labeled "Favorites Switch 1 Yes or No" -> Answer "Yes".

How it should work:

If you answer "Yes": The questions should reload and SHOW the second switch question labeled "Favorites Switch 2 Yes or No".
If you answer "No" or unanswer the question: The questions should reload and HIDE the second switch question labeled "Favorites Switch 2 Yes or No".
How it is working:
When you answer "Yes", the questions are reloaded and the second switch question is shown, but the screen flashes and the OnSwitchToggled event (see Controls/QuestionSwitchEntry.xaml.cs) gets called in an infinite loop where it keeps updating the "AnsweredBy" text until the whole app crashes.

Note: If you go to the List Views tab and try this, it works perfectly.

(https://github.com/user-attachments/assets/12f7d13a-61f6-4628-a576-e3613099c3c9)

Link to public reproduction project repository

https://github.com/pme442/CVIssueApp

Version with bug

9.0.110 SR11

Is this a regression from previous behavior?

No, this is something new

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

Any IOS version. I've seen it in 15, 16, 17, 18.

Did you find any workaround?

No

Relevant log output

[jfversluis]

Are you using CollectionViewHandler2? See: https://learn.microsoft.com/dotnet/maui/whats-new/dotnet-9?view=net-maui-9.0#collectionview-and-carouselview

I don't seem to see it in your repro project. If you do use that, does that resolve it?

[pme442]

OK, I have updated the repo to use CollectionViewHandler2. I also removed the null check on Parent in QuestionSwitchEntry.OnSwitchToggled() because the Parent seems to always be null now.
There are still problems.

Problem 1:

1. Start the app. It will default to the Collection Views Tab. That is where you want to be.
2. Select the 1st category (Facts) ->without scrolling up or down, find the switch question labeled "Facts Switch 1 Yes or No" -> Answer "No".
3. Select the 2nd category (Favorites) -> without scrolling up or down, find the switch question labeled "Favorites Switch 1 Yes or No" -> Answer "No".
   Result: Nothing happens. The AnsweredByText never changes and the questions answered count does not increase.

When I put a breakpoint in OnSwitchToggled and do Step 3, the newVal and the oldVal are both "No", so it falls out. The old value should not be "No", it should be "". I am wondering if this is a recycling issue. Is it picking up the binding from the Facts question just because it appeared in the same spot as the Favorites question (even though the CollectionView's ItemsSource changed and all of the items were re-drawn)?

Problem 2:

1. Start the app. It will default to the Collection Views Tab. That is where you want to be.
2. Facts -> Facts Switch 1 Yes or No -> Answer "No".
3. Facts -> Facts Switch 2 Yes or No -> Answer "No".
4. Favorites -> Favorites Switch 1 Yes or No -> Answer "Yes".
5. Favorites -> Favorites Switch 2 Yes or No -> Answer "Yes".
6. Select the Facts Category (to redraw the questions).
7. Select the Favorites Category (to redraw the questions).
   Result: App freezes. If you put a breakpoint in OnSwitchToggled(), you'll see it's in an infinite loop.

In my output window, it shows a couple of these messages:
2025-10-21 09:49:45.379479-0400 CVIssueApp[15801:195328] [CollectionView] Received layout attributes with an invalid index path. Attributes will be ignored. Attributes: <UICollectionViewLayoutAttributes: 0x106474da0; index path: (0-0); frame = (0 0; 243 65.5)>; layout: <Microsoft_Maui_Controls_Handlers_Items2_LayoutFactory2_CustomUICollectionViewCompositionalLayout: 0x106449160>; data source counts: [(0:0)]

(Here is a video of Problem 2)
https://github.com/user-attachments/assets/bf7ed88e-2035-4945-b6ba-0eceeec0db6c

[pme442]

Another thought: Is the problem my bindable property, "Value". That property should be bound to the Question.Value since the datatype of the entire control (QuestionSwitchEntry) is models:Question. (And it seems to work fine when the control is used in a ListView).
In OnSwitchToggled()
I replaced this line: var oldVal = Value == null ? "" : Value;
with this: var oldVal = question.Value == null ? "" : question.Value;
It seems like getting the old value directly from the binding context instead of relying on the bindable property, gives me the correct result.
Does that make any sense, or am I barking up the wrong tree?