On Apr 12, 2012, at 12:04 PM, Scott Andrew wrote:
> I have a question about retain cycles with ARC and blocks.
>
> I have the following code:
>
> __weak MyViewController* controller = self;
>
> [UIView animateWithDuration:.25 animations:^{
> controller.alpha = 0;
> }
> completion:^(BOOL finsihed) {
>
> [controller showState];
> }];
>
>
>
> -(void) showState {
> self.textView.text = self.stateText;
> }
>
> I have a question about what happens when I use self in showState. DId i just
> cause a reference counting issue where I now have an extra retain on self and
> it's not going to be cleaned up?
No. The compiler looks at the code _in the block_ to know what the block
should retain. It doesn't (for this purpose) look inside the -showState
method. It can't even reliably know for sure that the call to -showState in
the block refers to that implementation of -showState. For example, this code
could all be called from a superclass which overrides -showState.
> The WWDC video say to use weak pointers to self in the block otherwise there
> could be retain cycle issues. This is an example. The utility functions are
> actually quite larger and called from multiple places. I'm not creating the
> strong refrence via a variable because these blocks won't be called if self
> doesn't exist.
For this case, you don't even have to worry about referencing self in the
blocks directly. You don't need to use the weak copy, controller. First, the
object is not itself retaining the blocks. So, if the blocks retain self,
that's still not a retain cycle. Second, the blocks will be disposed of when
the animation completes. So any reference they hold on self is released when
that happens.
Regards,
Ken
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