[iOS] CollectionView item sizing wrong after refresh

[softeip]

Description of Change

Added reset of EstimatedItemSize and ItemSize when the size cache gets cleared

Issues Fixed

Fixes #20443

[softeip]

@dotnet-policy-service agree

[softeip]

What are the next steps for this PR?

[rmarinho]

/rebase

[rmarinho]

Can you try this with the main rebased ? It would use the new handler for collectionview2 . Also can we add a UITest? you can look at other examples with VerifyScreenshot.

[rmarinho]

Doesn't seem to fix #24961 and I think we ca drop the ItemSize

[softeip]

@rmarinho I was able to reproduce this issue with my app on 8.0.92 - I had different size views in the CollectionView and tried to refresh the collection several times and scrolling up and down. At some point I was able to reproduce the issue. I believe there are some steps missing on the way to reproduce this one for sure.

Then I updated to .NET 9 and MAUI 9.0.12 and I was able to reproduce that again. So new handler does not seem to have a fix.
Here is how it looks like.

[rmarinho]

@softeip are you using CollectionViewHandler2 ?

[softeip]

@rmarinho No, my bad. Added CollectionViewHandler2 manually and retested. Now I see that the issue is not reproducable no matter what I do and have many times I refresh the collection. I would say that the new handler fixes the sizing issue at least for my app.

[rmarinho]

@rmarinho No, my bad. Added CollectionViewHandler2 manually and retested. Now I see that the issue is not reproducable no matter what I do and have many times I refresh the collection. I would say that the new handler fixes the sizing issue at least for my app.

Nice, yeah that matches my testing, but this will fix using the CollectionView 1 and is still the default one.

[rmarinho]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

Seems is failing some tests

https://dev.azure.com/xamarin/public/_build/results?buildId=130473&view=ms.vss-test-web.build-test-results-tab&runId=3488872&resultId=100059&paneView=debug

[rmarinho]

OK after playing with it seems the issue is setting EstimatedSize when the CollectionView ItemsSource is disposed is the problem, we actually want clear that when our constrains change in case of the refresh for example.

[Redth]

Do we use empty specifically to know we need to estimate the size?

Just wanting to make sure we shouldn't be using UICollectionViewFlowLayout.AutomaticSize which has a specific meaning (and is not equivalent to Empty). I am guessing we want Empty here since we do the manually measurement on CV1 still, but wanted to be sure.

[softeip]

Looks like no, we should not use automatic size.
There is a call to ConstrainTo() method which is implemented in the ItemsViewLayout subclasses. Their implementation calls DetermineCellSize() which have some checks for EstimatedItemSize == CGSize.Empty. There is a comment saying about <iOS 10 fix (237 line in this file). Using UICollectionViewFlowLayout.AutomaticSize can lead to crashes and would require further fixes.