How can a weakly retained block cause a retain cycle when capturing “self”

I have a class with a property which is a weak reference to a block.

@interface BlockTest : NSObject
    @property (nonatomic, weak) void(^testBlock)();
@end

At another point in the class I use this block like this:

  • How can I compute a SHA-2 (ideally SHA 256 or SHA 512) hash in iOS?
  • Generic typeof for weak self references
  • Can a viewcontroller access the identifier of an incoming segue?
  • How to add more localizations to my Xcode Project?
  • How to move a view along a curved path in iOS
  • use of @property and @synthesise?
  • - (void)foobar {
        self.testBlock = ^{
            [self doSomething];
        };
    }
    

    The compiler (Apple LLVM 3.0) complains that there might be a retain cycle because self is strongly captured here. But I fail to see how this leads to a retain cycle because the block itself is a __weakreference, so it should be fine. If I understood ARC weak references correctly, when the -foobar method returns the block passed to self.testBlock should be deallocated (if not held elsewhere) and thus also release self.

    What’s the reason the compiler still thinks there might be a retain cycle?

    Solutions Collect From Internet About “How can a weakly retained block cause a retain cycle when capturing “self””

    Blocks strongly capture objects within them regardless of how the block itself is referenced. The retain cycle warning is just that, a warning of the possibility. If you know based on the context of your app that this use will not cause a retain cycle you can safely ignore it. To get rid of the warning, you can pass self through an intermediary, strong or weak, as follows:

    __weak typeof(self) weakSelf = self;
    self.testBlock = ^{
        [weakSelf doSomething];
    };
    

    I’d change your block property to be a strong reference and do the above.