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Crash when adding a section before view appears #8

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JosephDuffy opened this issue Sep 7, 2020 · 3 comments
Open

Crash when adding a section before view appears #8

JosephDuffy opened this issue Sep 7, 2020 · 3 comments
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bug Something isn't working

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@JosephDuffy
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Describe the bug

When adding a section to a ComposedSectionProvider in a viewDidLoad after the CollectionCoordinator has been set as the delegate but before the view has appeared the coordinator will fatalError in elementsProvider(for:) with error Fatal error: No UI configuration available for section 2.

To Reproduce

  1. Checkout https://github.com/composed-swift/Composed-Demo/tree/ComposedSectionProvider-crash-example
  2. Uncomment https://github.com/composed-swift/Composed-Demo/blob/ComposedSectionProvider-crash-example/Composed-Demo/Collection/PeopleCollectionViewController.swift#L20

Expected behavior

Should not crash

Environment

  • OS Version: iOS 13.5, iOS 14 beta 7
  • Library Version: 1.0.2
  • Device: iPhone 8 Simulator

Additional context

The crash is triggered by collectionView.performBatchUpdates, but the closure is never executed so prepareSections never gets a chance to be called.
@JosephDuffy JosephDuffy added the bug Something isn't working label Sep 7, 2020
@shaps80
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shaps80 commented Sep 9, 2020 •
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Any suggested fix? I kinda get the issue, but I'm not sure off-hand the most appropriate fix. Seems we'd need to know somehow that its 'detached'? Or perhaps I'm misunderstand the issue?

@shaps80
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shaps80 commented Sep 11, 2020

Is this resolved from the PR I just merged related to performBatchUpdates or is this a separate issue?

@JosephDuffy
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Is this resolved from the PR I just merged related to performBatchUpdates or is this a separate issue?

I tried the change but it didn't fix this. It could be something similar though so worth thinking about.

JosephDuffy added a commit that referenced this issue Nov 3, 2020
@JosephDuffy
Potential fix for invalidation crashes
8f0d651 
As mentioned in #13 and #8 there are some scenarios where the collection view’s data is out-of-sync with the data in composed.

As mentioned in #13 calling `layoutIfNeeded` can trigger the data to be in sync again. In this I have added it to `mappingWillBeginUpdating(_:)` which _appears_ to solve the problem.

It might be needed in `replace(sectionProvider:)` (because `reloadData` is called) and/or `mappingDidInvalidate(_:)` (for the same reason) but I’m still investigating.
@JosephDuffy JosephDuffy mentioned this issue Nov 3, 2020
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@shaps80 @JosephDuffy