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Editorial Team
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Asked: 2026-06-02T05:06:11+00:00

I have a UITableView which displays images. Every cell has an image and every

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I have a UITableView which displays images. Every cell has an image and every time a cell loads, I call a selector (from the cellForRowAtIndexPath) in the background like this:

[self performSelectorInBackground:@selector(lazyLoad:) withObject:aArrayOfData];

The only problem is that sometimes I get a crash (because I am changing data in the background while it’s trying to be read elsewhere). Here’s the error:

*** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <CALayerArray: 0xce1a920> was mutated while being enumerated.'

When updating the data in the background, should I move it to the main selector and change it? Or should I call the @selector() differently?

Thanks!

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1 Answer

  1. Editorial Team

    If you can leave the operation on the main thread and have no lagginess nor problems you are done.

    However: Let’s assume you’ve already done that and encounter problems. The answer is: don’t modify the array in the lazy load. Switch to the main thread to modify the array. See Brad’s answer here:

    https://stackoverflow.com/a/8186206/8047

    for a way to do it with blocks, so you can send your objects over to the main queue (you should probably also use GCD for the call to the lazy load in the first place, but it’s not necessary).

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