Why the retain cycle warning not thrown?

Question

I use Xcode 5 and have some code

@interface Controller {
    __weak IBOutlet UIView *someView;
}

@implementation Controller {

- (void)doSomething
{
    [UIView animateWithDuration:0.5 animations:^{
        someView.hidden = YES;
    }];
}

- (void)doSomething1
{
    [UIView animateWithDuration:0.5 animations:^{
        [self doSomething];
    }];
}

Why the retain cycle warning not thrown there? Should I use weak references on self every time I use self in blocks?

Also I enabled Implicit retain of self within blocks warning and it gave me 100 warnings with advice to write self->ivar.prop (not ivar.prop) in blocks. Should I do so after that warning is disabled by default?

score 4 · Accepted Answer · edited May 23 '17 at 11:53

4

Why the retain cycle warning not thrown there?

The block retains you, but you don't retain the block. It'll be destroyed after animation is complete. So, no cycles.

Should I use weak references on self every time I use self in blocks?

If your block doesn't get destroyed automatically (e.g. a recurring timer), then you should.

Should I do so after that warning is disabled by default?

Depends upon the context. Again, if your blocks live for a long time, you might want to declare non-retained weakSelf.

But basically you're fine if your blocks don't get saved somewhere.

See also How do I avoid capturing self in blocks when implementing an API?

edited May 23 '17 at 11:53

Community

1
1

answered Sep 27 '13 at 11:21

ilya n.

18,398
15
71
89

Thanks for clarification. I missed that block is retained only if it is stored. – efpies Sep 27 '13 at 11:57
What does it mean for a block to be "long lived"? All blocks have a finite number of lines of code, so it will eventually exit. – Pwner Feb 17 '15 at 21:19

score 3 · Answer 2 · edited May 23 '17 at 11:53

3

This is not a retain cycle. This is two methods calling each other in a loop. A retain cycle happens when two object instances have strong (retained) references to each other that are never broken, and those two objects remain in memory unnecessarily.

Example with code: Retain cycle in ARC

edited May 23 '17 at 11:53

Community

1
1

answered Sep 27 '13 at 11:06

bneely

9,083
4
38
46

score 0 · Answer 3 · answered Oct 04 '13 at 09:50

Should I use weak references on self every time I use self in blocks?

Absolutely not. Blocks retain captured object pointers for a reason -- to keep the objects alive until so that they'll still be there when the block is run. If there is no retain cycle and there is no other thing keeping a reference to the object pointed to by self, it could be deallocated before the block is run (asynchronously, for example).

Why the retain cycle warning not thrown?

3 Answers3