Referring to weak self inside a nested block

问题:

Suppose I already create a weak self using

__weak typeof(self) weakSelf = self;
[self doABlockOperation:^{
        ...
    }];

Inside that block, if I nest another block:

[weakSelf doAnotherBlockOperation:^{
            [weakSelf doSomething];
}

will it create a retain cycle? Do I need to create another weak reference to the weakSelf?

__weak typeof(self) weakerSelf = weakSelf;
[weakSelf doAnotherBlockOperation:^{
                [weakerSelf doSomething];
    }

回答1:

It depends.

You only create a retain cycle if you actually store the block (because self points to the block, and block points to self). If you don't intend to store either of the blocks, using the strong reference to self is good enough --- block will be released first after it got executed, and then it will release it's pointer to self.

In your particular example, unless you're performing more operations which are not shown, you don't need to create any weakerWeakerEvenWeakerSelfs.

回答2:

Your code will work fine: the weak reference will not cause a retain cycle as you explicitly instruct ARC not to increase the retainCount of your weak object. For best practice, however, you should create a strong reference of your object using the weak one. This won't create a retain cycle either as the strong pointer within the block will only exist until the block completes (it's only scope is the block itself).

__weak typeof(self) weakSelf = self;
[self doABlockOperation:^{
    __strong typeof(weakSelf) strongSelf = weakSelf;
    if (strongSelf) {
        ...
    }
}];