How to Correctly handle Weak Self in Swift Blocks with Arguments
If self could be nil in the closure use [weak self].
If self will never be nil in the closure use [unowned self].
If it's crashing when you use [unowned self] I would guess that self is nil at some point in that closure, which is why you had to go with [weak self] instead.
I really liked the whole section from the manual on using strong, weak, and unowned in closures:
Note: I used the term closure instead of block which is the newer Swift term:
Difference between block (Objective C) and closure (Swift) in ios
**EDITED for Swift 4.2:
As @Koen commented, swift 4.2 allows:
guard let self = self else { return // Could not get a strong reference for self :`(}// Now self is a strong referenceself.doSomething()P.S.: Since I am having some up-votes, I would like to recommend the reading about escaping closures.
EDITED: As @tim-vermeulen has commented, Chris Lattner said on Fri Jan 22 19:51:29 CST 2016, this trick should not be used on self, so please don't use it. Check the non escaping closures info and the capture list answer from @gbk.**
For those who use [weak self] in capture list, note that self could be nil, so the first thing I do is check that with a guard statement
guard let `self` = self else { return}self.doSomething()If you are wondering what the quote marks are around self is a pro trick to use self inside the closure without needing to change the name to this, weakSelf or whatever.
Put [unowned self] before (text: String)... in your closure. This is called a capture list and places ownership instructions on symbols captured in the closure.