如何解决此 CollectionView 崩溃? [英] How to solve this CollectionView crash?

问题描述

我的应用有两个 CollectionViewController.在给定时间只有一个可见.

My app has two CollectionViewControllers. Only one is visible at a given time.

我在情节提要上创建了以下结构:两个容器视图相互叠加.每个容器视图都嵌入了一个 CollectionViewController.特定容器视图的可见性决定了哪个 collectionViewController 可见.

I have created the following structure on storyboard: two container views on top of each other. Every container view has a CollectionViewController embedded. The visibility of a particular container view determines which collectionViewController is visible.

这就是问题所在.两个 CollectionViewController 都在并行接收数据，但是 iOS 有一个错误，如果一个 CollectionViewController 在不可见的情况下尝试使用 performBatchUpdates 执行插入，则会导致应用崩溃.

This is the problem. Both CollectionViewControllers are receiving data in parallel but iOS has a bug that will make the app crash if one CollectionViewController tries to execute an insert using performBatchUpdates while it is invisible.

为了防止这种情况，我在两个 CollectionViewController 上都创建了一个 BOOL 标志，这样他们就可以知道它们是否可见并执行 performBatchUpdates.比如:

Trying to prevent that, I have created a BOOL flag on both CollectionViewControllers so they can know if they are visible and execute or not the performBatchUpdates. Something like:

if (self.isThisCollectionViewVisible == NO) return;

[self.collectionView performBatchUpdates:^{
   // bla bla... perform insert,m remove...

这解决了部分问题.但是应用程序在以下情况下继续崩溃:如果我点击按钮切换到不可见的 CollectionViewController 使其在接收更新时可见.

This solves part of the problem. But the app continues to crash on the following condition: if I tap the button to switch to the invisible CollectionViewController making it visible while it is receiving updates.

我的意思是:让 A 第一个 CollectionViewController 和 B 第二个.A 是可见的，而 B 在这一点上是不可见的.B 开始接收数据并尝试执行 performBatchUpdates 但由于它不可见，因此 if (self.isThisCollectionViewVisible == NO) 返回；正在阻止 performBatchUpdates 运行，这很好.现在我使 A 不可见，而 B 可见.此时标志 self.isThisCollectionViewVisible 设置为 YES 并且 performBatchUpdates 使应用程序崩溃并出现以下错误:

I mean this: lets call A the first CollectionViewController and B the second one. A is visible and B is invisible at this point. B starts receiving data and is trying to do a performBatchUpdates but as it is invisible, the if (self.isThisCollectionViewVisible == NO) return; is preventing performBatchUpdates to run, what is fine. Now I make A invisible and B visible. At this point the flag self.isThisCollectionViewVisible is set to YES and performBatchUpdates makes the app crash with this error:

* -[CollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:] 中的断言失败，/BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3512.60.7/UICollectionView.m:4625* 由于未捕获的异常NSInternalInconsistencyException"而终止应用程序，原因:无效更新:无效第 0 节中的项目数.包含在第 0 节中的项目数更新后的现有节(76)必须等于更新前该部分中包含的项目 (70)，加号或减号从该部分插入或删除的项目数(插入 5 个，2 已删除)和加减移入或移出的项目数该部分(0 移入，0 移出).'

* Assertion failure in -[CollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3512.60.7/UICollectionView.m:4625 * Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (76) must be equal to the number of items contained in that section before the update (70), plus or minus the number of items inserted or deleted from that section (5 inserted, 2 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).'

我认为 CollectionViewController 确实还没有准备好并更新到能够执行 performBatchUpdates... 这不是不更新数据源的问题以前是因为它正在更新.

I think the CollectionViewController is really not yet ready and updated to be able to do a performBatchUpdates... and this is not a matter of not updating the data source previously because it is being updated.

我可以做哪些检查来防止这种情况发生?

What checks can I do to prevent that from happening?

注意:我特别注意到这次崩溃有一些奇怪的地方.它说正在插入 5 个元素并删除了 2 个元素，但实际上当崩溃发生时正在插入 3 个元素，删除了 0 个元素并更改了 2 个元素.

NOTE: I noticed something strange about this crash in particular. It says that 5 elements are being inserted and 2 deleted but in fact 3 elements are being inserted, 0 deleted and 2 changed when the crashes happen.

推荐答案

为我添加 self.collectionView.numberOfItemsInSection(0) 修复了崩溃.collectionView 在不可见时插入项目时出现问题.

For me adding self.collectionView.numberOfItemsInSection(0) fixed the crash. The collectionView has issues while inserting items when it is not visible.

似乎我的解决方案并不孤单:http://www.openradar.me/15262692

Seems like I'm not alone with my solution: http://www.openradar.me/15262692

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