Nested blocks and references to self

问题

I have a block wherein I use self so I declare a weak reference to self:

__weak MyClass *weakSelf = self;

Now my questions:

1. I get an error where I define weakSelf and I don't understand what this should mean.:

   weak attribute can not be specified on an automatic variable

2. Inside my block I pass weakSelf to another block and I am not sure if I now have to do the same thing again like so:

   __weak MyClass *weakWeakSelf = weakSelf;
   

   And then pass weakWeakSelf to that block?

回答1:

This is most likely occurring as you are targeting down to iOS 4. You should change it to be

__unsafe_unretained MyClass *weakWeakSelf = weakSelf;

回答2:

With ARC

__weak __typeof__(self) wself = self;

Wihtout ARC

__unsafe_unretained __typeof__(self) wself = self;

回答3:

With libextobjc it will be readable and easy:

- (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];

        }];
    }];
}

来源：https://stackoverflow.com/questions/10431110/nested-blocks-and-references-to-self