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A Problem Encountered in Development

How to correctly use a block’s weakSelf and strongSelf in Objective-C across multiple nested blocks

In Objective-C, weak self and strong self are used to solve the problem of retain cycles. When you use self as a parameter of a block, you need to use __weak typeof(self) weakSelf = self; to create a weak reference in order to avoid a retain cycle. Then, inside the block, you can use strongSelf to obtain a strong reference.

The following is an example showing how to use weak self and strong self in a three-layer nested method:

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- (void)outerMethod {
    __weak typeof(self) weakSelf = self;
    [self innerMethod1:^{
        __weak typeof(weakSelf) weakSelf2 = weakSelf;
        [weakSelf2 innerMethod2:^{
            __weak typeof(weakSelf2) weakSelf3 = weakSelf2;
            [weakSelf3 innerMethod3:^{
                __strong typeof(weakSelf3) strongSelf = weakSelf3;
                // 在这里使用strongSelf进行操作
            }];
        }];
    }];
}

- (void)innerMethod1:(void (^)(void))completion {
    // ...
    if (completion) {
        completion();
    }
}

- (void)innerMethod2:(void (^)(void))completion {
    // ...
    if (completion) {
        completion();
    }
}

- (void)innerMethod3:(void (^)(void))completion {
    // ...
    if (completion) {
        completion();
    }
}

In this example, we use __weak typeof(self) weakSelf = self; to create a weak reference in each layer’s method, and in the next layer we use __weak typeof(weakSelf) weakSelf2 = weakSelf;. Finally, in the innermost method, we use __strong typeof(weakSelf3) strongSelf = weakSelf3; to obtain a strong reference for use within that layer’s method.