When assign a weak variable to a strong variable

Question

When I reading SDWebImage source code, I found a snippet

if (url)
{
    __weak UIButton *wself = self;
    id<SDWebImageOperation> operation = [SDWebImageManager.sharedManager downloadWithURL:url options:options progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished)
    {
        __strong UIButton *sself = wself;
        if (!sself) return;
        if (image)
        {
            [sself setBackgroundImage:image forState:state];
        }
        if (completedBlock && finished)
        {
            completedBlock(image, error, cacheType);
        }
    }];
    objc_setAssociatedObject(self, &operationKey, operation, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

It is easy to understand that for avoiding the retain cycle, it uses __weak keyword for the self, however, why it assigns wself to a strong variable sself, won't the block be still retain the self.

@Danyun `self` is an strong but it is out of the block scope, so the block will retain it. `sself` is strong but it is in the block scope, it will be released at the end of the block, so no circle. — KudoCC, Mar 27 '14 at 07:57
@KudoCC It sound reasonable. I will accept it if you post your comment as an answer. — Danyun Liu, Mar 27 '14 at 08:04

score 1 · Accepted Answer · edited May 23 '17 at 11:57

1

self is an strong but it is out of the block scope, so the block will retain it. sself is strong but it is in the block scope, it will be released at the end of the block, so no circle.

BTW the correct answer of this question is a good explanation about the block circle.

edited May 23 '17 at 11:57

Community

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answered Mar 27 '14 at 08:26

KudoCC

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When assign a weak variable to a strong variable

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