Is it necessary to use [unowned self] in closures of UIView.animateWithDuration(...)?

Question

    UIView.animateWithDuration(1,         animations: { [unowned self] in             self.box.center = self.boxTopRightPosition         },         completion: { [unowned self] completed in             self.box.hidden = true     }) 

Is it necessary to avoid memory leak?

Answer 1

No, it is not needed in this case. animations and completion are not retained by self so there is no risk of strong retain cycle.

Answer 2

Well, "necessary" isn't the same as "recommended". If your question is if it's necessary then @Kirsteins' response is fine, however imagine the situation where you want to animate something in your view controller after some work, but your view controller has been released (because it is not in the view hierarchy anymore or any other reason). In this case, if you don't use [weak self], your view controller won't get released until finishing the animation because you are retaining it in the animation block, but does it make sense to keep it retained until animating something which is not in the view anymore?

So, in few words, you don need to use a weak reference to self when animating UIKit, however, you don't need to keep your view retained if it's released, because an animation with no view doesn't make sense, so using weak is a good option.