Warning in Xcode 8: Instance method nearly matches optional requirement

Question

I am trying to implement local notifications in iOS10, and so far it is not working.

I get this warning around my delegate methods:

Instance method 'userNotificationCenter(_:didReceive:withCompletionHandler:)'     
nearly matches optional requirement 'userNotificationCenter(_:didReceive:withCompletionHandler:)'
of protocol 'UNUserNotificationCenterDelegate'

As solution xcode suggests two options: 1.make it private 2.make it @nonobjc

Why is that? Why do I need to do it? And most important, how to make these methods work?

did you find a solution to this? – user2363025 Jan 04 '17 at 17:37 — user2363025, Jan 04 '17 at 17:37

TwoStraws · Answer 1 · 2016-09-07T23:04:16.420

3

Xcode 8 beta 6 introduced many Swift 3 changes, one of which is the @escaping keyword to mark closures that might be used after a method returns. Completion handlers are usually escaping closures, because you might show some information to the user, wait for feedback, and then call the completion handler – the method will return and keep a reference to the closure, rather than blocking.

I expect there will be an Xcode 8 GM issued in the next few hours, but right now Xcode doesn't insert the @escaping attribute where it's needed, which is probably what's causing your error. The two Fix-its being offered are red herrings, I'm afraid.

Try writing your method like this instead:

func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {

Edit: Xcode 8 GM is now available, and correctly inserts @escaping when needed.

edited Sep 07 '16 at 23:04

answered Sep 07 '16 at 14:23

TwoStraws

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I installed xcode8 GM, still see sem issue, and it's not putting @escaping there, and when I put it - it says "unknown attribute escaping" – Async- Sep 12 '16 at 13:55
It's definitely correct; are you sure you're in Xcode 8? – TwoStraws Sep 12 '16 at 14:00
pls see my image in the question (I am also using SWIFT2.3, instead of 3) – Async- Sep 12 '16 at 14:20
You rock dude, fixed my issue – Burf2000 Sep 28 '16 at 14:50

score 0 · Answer 2 · edited Oct 06 '16 at 13:29

I have a line like this:

func textFieldShouldReturn(textField: UITextField) -> Bool {...}

Xcode gives me the same "nearly matches optional requirement" warning. Xcode 8.0 GM fixit gives me two choices to silence the warning. Add private keyword:

 private func textFieldShouldReturn(textField: UITextField) -> Bool {...}

or add @nonobjc clause :

@nonobjc func textFieldDidEndEditing(textField: UITextField) {...}

Either one shuts it up, but I am not sure which one is more preferable. When I tried @ escaping I get an error "@ escaping may only be used on 'parameter' declarations'.

Warning in Xcode 8: Instance method nearly matches optional requirement

2 Answers2