Re: Block gets NULL-ified when animation completes
Re: Block gets NULL-ified when animation completes
- Subject: Re: Block gets NULL-ified when animation completes
- From: Vlad Alekseev <email@hidden>
- Date: Thu, 15 Aug 2013 16:41:04 +0400
Turns out, this is a bug in UICollectionView or even ARC. And it is easily reproducible. You can download Apple's sample code:
http://developer.apple.com/library/ios/samplecode/CollectionView-Simple/Introduction/Intro.html
and modify it to return 0 items to the collection view. Then try to perform the following code:
dispatch_block_t block = ^{
printf("finished");
};
UICollectionViewFlowLayout *layout = (UICollectionViewFlowLayout *)self.collectionView.collectionViewLayout;
[self.collectionView performBatchUpdates:^{
layout.minimumInteritemSpacing = 20;
} completion:^(BOOL finished) {
block();
}];
It will crash since `finish` will be `nil`. But if you make data source to return non-zero item count to the collection view then everything will work good.
Created a bug report with ID 14744561. Affects iOS 6.0 and above.
You may refer to the Apple Dev Forums discussion thread: https://devforums.apple.com/thread/198531?tstart=0
Thanks!
Vlad.
15 авг. 2013 г., в 9:25, Vlad Alekseev <email@hidden> написал(а):
> Hey,
>
> ARC should drive this for me. If it wouldn’t, then it wouldn’t work in case if there are items in the collection view.
> Tried to copy manually - no results. BTW, not only «finish», but also «completion» gets NULLified at the last step.
>
> Vlad.
>
> 15 авг. 2013 г., в 9:22, Jens Alfke <email@hidden> написал(а):
>
>> Sounds like you forgot to copy the block — if it’s being invoked after the calling function returns (as a completion handler would) it needs to be copied so it can survive the loss of its original stack frame.
>>
>> —Jens
>
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