[Bug] [iOS] CollectionView visible cells not updating correctly when using XCT ObservableRangeCollection after recent semaphore fix

[GalaxiaGuy]

Description

I have a CollectionView.ItemsSource bound to an ObservableRangeCollection from Xamarin Community Toolkit.
Some time after being initially shown, some items are removed and some items are added using AddRange and RemoveRange.

The visible cells do not change.

I don't know if the bug is in Forms, or XCT, but this worked fine in Forms versions without this fix: #11853

Steps to Reproduce

1. Bind CollectionView.ItemsSource to ObservableRangeCollection.
2. Use AddRange and/or RemoveRange on the items.

Expected Behavior

Visible items change.

Actual Behavior

Visible items do not change.

Scrolling the items off screen and back on fixes the cells.

Basic Information

• Version with issue: 4.8.0.1821, 5.0.0.1905
• Last known good version: 4.8.0.1687
• NuGet Packages: Xamarin Community Toolkit 1.0.2
• Affected Devices: iOS

Reproduction Link

https://github.com/GalaxiaGuy/xf-bugs/tree/bug/observablerangecollection
https://github.com/GalaxiaGuy/xf-bugs/archive/bug/observablerangecollection.zip

Click the button to push a new page. 100ms after the page is created all the cells should be green and not say "Loading".

Workaround

Just using ObservableCollection seems to work.

[GalaxiaGuy]

Just using ObservableCollection seems to work.

Although this is true in the small test case, it does not seem to be true in the app I'm currently working on. When using ObservableCollection the visible cells update, but all change to have the same content as the last visible cell (again scrolling a cell off screen back on again fixes it).

I realise not having a a reproduction makes it hard to do anything, I include just as further evidence that something strange is going on.

[Tommigun1980]

Just using ObservableCollection seems to work.
I realise not having a a reproduction makes it hard to do anything, I include just as further evidence that something strange is going on.

I think this may be the same issue as #13126 (comment), as that issue is using an OptimizedObservableCollection with AddRange (that sends RESET events)?