Should I use a weak references with properties of a property and blocks / ARC?

Question

I know that when we're using ARC and blocks, we should use __weak to prevent capturing strongly self and prevent a retain cycle ! But I was wondering if in the following example I need to use __weak ?

__weak MyViewController *weakSelf = self;
[self.personObject.gallery downloadLogoCompletionBlock:^(UIImage *image) {
                                        if (image) {
                                            weakSelf.logoImageView.image = image;
                                        }];

Gallery is retaining the block not self, right ? If so I could write :

self.logoImageView.image = image;

Thanks for your answers

Yeah that looks reasonable to me, however given you are calling a method in self anyway, it might not be necessary. — trojanfoe
Can you provide the implementation of the downloadLogoCompletionBlock: method? It will tell us if you are running into a retain cycle. — Pedro Mancheno
You should create a strong reference to self inside your block and assign the weakReference to it. — JonahGabriel

Martin R Martin R · Accepted Answer · 2013-10-17T14:40:58

With a strong reference self inside the block you would have a (temporary) retain cycle

self -> _personObject -> _gallery -> BLOCK -> self

assuming that the properties personObject, gallery are backed up by instance variables _personObject, _gallery. The retain cycle will be "destroyed" as soon as the completion block is called. If the completion block is never called then self can never be deallocated.

Therefore, if self should possibly be deallocated before the completion block is called, you should use a weak reference.

Should I use a weak references with properties of a property and blocks / ARC?

3 Answers