嵌套块和对自身的引用

Question

>我有一个块，我在其中使用self所以我声明了一个对self的弱引用：

__weak MyClass *weakSelf = self;

现在我的问题：

1. 我在定义weakSelf时收到一个错误，我不明白这应该是什么意思。

   不能在自动变量上指定弱属性

2. 在我的块内，我weakSelf传递到另一个块，我不确定我现在是否必须像这样再次做同样的事情：

   __weak MyClass *weakWeakSelf = weakSelf;
   

   然后把weakWeakSelf传给那个街区？

Answer 1

这很可能发生在您瞄准iOS 4时。您应该将其更改为

__unsafe_unretained MyClass *weakWeakSelf = weakSelf;

Answer 2

with ARC

__weak __typeof__(self) wself = self;

无电弧

__unsafe_unretained __typeof__(self) wself = self;

Answer 3

使用 libextobjc，它将是可读且简单的：

- (void)doStuff
{
    @weakify(self); 
    // __weak __typeof__(self) self_weak_ = self;
    [self doSomeAsyncStuff:^{
        @strongify(self);
        // __strong __typeof__(self) self = self_weak_;
        // now you don't run the risk of self being deallocated
        // whilst doing stuff inside this block 
        // But there's a chance that self was already deallocated, so
        // you could want to check if self == nil
        [self doSomeAwesomeStuff];
        [self doSomeOtherAsyncStuff:^{
            @strongify(self);
            // __strong __typeof__(self) self = self_weak_;
            // now you don't run the risk of self being deallocated
            // whilst doing stuff inside this block 
            // Again, there's a chance that self was already deallocated, so
            // you could want to check if self == nil
            [self doSomeAwesomeStuff];
        }];
    }];
}