[Bug] [ios] CollectionView crashes on iOS when adding new groups (repro included) Also slows down when SectionHeadersPinToVisibleBounds is true

[softlion]

Description

Steps to Reproduce

Repro: https://github.com/vapolia/ReproCollectionViewGroupCrash

1. Add a CollectionView with IsGrouped set to true
2. Add a datasource containing 1 group (groups are an ObservableCollection, items in groups are in an ObservableCollection too)
3. Init the UI, then after 1 second, remove the 1st group, then add 2 new groups.

Expected Behavior

2 groups displayed in the collection vuew

Actual Behavior

crash

Basic Information

• Version with issue: all
• Last known good version: none
• Platform Target Frameworks:
  • iOS:

Reproduction Link

https://github.com/vapolia/ReproCollectionViewGroupCrash

Workaround

Add Task.Delay(1) after each unit change involving groups.

additional info:

• quickly adding normal items to the collection view Will also crash it. Adding task delay fix it.

• setting sectionHeadersPinToVisibleBounds To true through a custom renderer slows down the scrolling very very hard. It also triggers a leak as the slowdown increases with the scrolls.
  This one has also been reported by someone on stackoverflow https://stackoverflow.com/questions/70947521/scroll-hangs-in-collection-view-when-sectionheaderspintovisiblebounds-is-used-in

Repro is easy:

    public class MyCollectionViewRenderer : CollectionViewRenderer
    {
        //Slow down scroll hard then crash !!
         protected override ItemsViewLayout SelectLayout()
         {
             var layout = base.SelectLayout();
             if (layout is UICollectionViewFlowLayout flow)
                 flow.SectionHeadersPinToVisibleBounds = true;
             return layout;
         }
    }

[tarunagrawal1990]

Any workaround for this issue, till the time new version get released.

[softlion]

Any workaround for this issue, till the time new version get released.

Read workaround in issue :)

[softlion]

Note there is no workaround for the slowness.

The slowness appears whenever the collectionview's control height changes from its top. Repro is simple: add a vertical full screen stacklayout, a label and a collectionview that fills the remaining space. Set IsVisible to false on the label by default. Then trigger IsVisible to true on the label 5 secondes after the UI is displayed.

The collectionview scroll will becore VERY VERY slow.