On Jan 26, 2012, at 1:51 PM, Jan E. Schotsman wrote:
> Hello,
>
> This code is given in the "Transitioning to ARC Release Notes" as an example
> of accomodating blocks in an ARC environment:
>
> __block MyViewController *myController = [[MyViewController alloc] init…];
> // ...
> myController.completionHandler = ^(NSInteger result) {
> [myController dismissViewControllerAnimated:YES completion:nil];
> myController = nil;
> };
>
> Supposedly this avoids a retain cycle. But where is the cycle? At least two
> objects are needed for a cycle. What is the second one?
> Excuse me if I'm being dumb.
myController retains/copies the block. Then the block retains myController
(under ARC __block variables are strong references, so they get retained). Thus
you are left with myController retains the block which retains myController.
--
David Duncan
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