ios - block 内不允许解除对 __weak 指针的引用

Question

Apple docs假设我可以通过捕获对 self 的弱引用来避免强引用循环，如下所示:

- (void)configureBlock {
    XYZBlockKeeper * __weak weakSelf = self;
    self.block = ^{
        [weakSelf doSomething];   // capture the weak reference
                                  // to avoid the reference cycle
    }
}

然而当我写这段代码时，编译器告诉我:

Dereferencing a __weak pointer is not allowed due to possible null value caused by race condition, assign it to strong variable first

然而，下面的代码不会创建一个强引用循环，并可能泄漏内存吗？

- (void)configureBlock {
    XYZBlockKeeper *strongSelf = self;
    self.block = ^{
        [strongSelf doSomething];
    }
}

Answer 1

你应该像这样使用:例如:

__weak XYZBlockKeeper *weakSelf = self;

self.block = ^{

    XYZBlockKeeper *strongSelf = weakSelf;

    if (strongSelf) {
        [strongSelf doSomething];
    } else {
        // Bummer.  <self> dealloc before we could run this code.
    }
}