[CollectionView] Fix crash on iOS adding items (ObservableCollection)

[jsuarezruiz]

Description of Change

Both, CollectionView and CarouselView, had a crash when adding items to a binder ObservableCollection (mainly played using asynchronous calls, etc.).

The native error was something like:
"Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (1) must be equal to the number of items contained in that section before the update (1), plus or minus the number of items inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out)".

NOTE: We could get the same error in other cases (removing items, etc).

Using performBatchUpdates the item count returned by collectionView(_:numberOfItemsInSection:) should be sync with the updates made inside. We had a mismatch sometimes between the number of items in the ObservableCollection and the UICollectionView.

This article describe a similar issue: https://fangpenlin.com/posts/2016/04/29/uicollectionview-invalid-number-of-items-crash-issue/

Issues Resolved

• fixes [Bug] Crash on CarouselView using ObservableCollection #7678

API Changes

None

Platforms Affected

• Core/XAML (all platforms)
• iOS

Behavioral/Visual Changes

None

Before/After Screenshots

Before

After

Testing Procedure

Launch Core Gallery and navigate to the Issue 7678. Without a crash, everything is working fine.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[rmarinho]

retarget 4.3 and a UItest pleaaasseeee :)

[samhouts]

@jsuarezruiz needs rebase. also, a uitest would be snazzy

[adrianknight89]

I'm encountering this error lately when I go from 0 items to adding an item to the items source after CollectionView is rendered.

[samhouts]

@jsuarezruiz please rebase :)

[jsuarezruiz]

@samhouts Done!. This is an issue repeated several times, what do you think if I include several tests?

[rmarinho]

We have a gallery for this case in CollectionView no? maybe we just need to add more UItests to that gallery

[RhomGit]

Is there any news on this?
Also, somewhat related ... how do you test workarounds on iOS 12 if you don't have a physical device? Visual Studio emulators are all iOS 13.

[berlamont]

@RhomGit
If you go into xcode preferences on your Mac you can download older simulator images on the components tab

[RhomGit]

@berlamont Thanks for your advice, I have taken a look and it works as you say, excellent. Unfortunately (or fortunately since we didn't roll it out) our workaround for this issue did not work but at least now we have something to test against.

[jfversluis]

Failing unit test?

[samhouts]

@jsuarezruiz Also, please retarget to 4.3.0