NotificationCenter observer clearing after presenting modal

Question

My app is playing a video and I want to trigger an action when the video ends. The screen (A) is embedded in a navigation controller, and if I trigger a push (to B) and then come back (to A), the action (in A) still takes place based on the observer. There is also an option in my screen that triggers a modal (to C) which then gets dismissed to go back (to A). When I come back from the modal (C), however, the observer (in A) is gone.

Here's my code for screen A's view controller:

ScreenAViewController: UIViewController {
    override func viewDidLoad() {

        super.viewDidLoad()
        // Do more stuff

        NotificationCenter.default.addObserver(forName: .AVPlayerItemDidPlayToEndTime, object: self.avPlayer.currentItem, queue: .main) { _ in
            // Do stuff
        }
    }
}

Here's the code that trigger the modal to screen C:

@IBAction func triggerModal(_ sender: UIButton) {
    avPlayer.pause()
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let screenCViewController = storyboard.instantiateViewController(withIdentifier: "ScreenC") as! ScreenCViewController
    present(screenCViewController, animated: true)
}

And finally here's the line that dismisses screen C:

dismiss(animated: true, completion: nil)

What exactly do you mean when you say "[...] the observer (in A) is gone [...]"? — André Slotta, Dec 25 '18 at 14:36

score 0 · Answer 1 · answered Dec 24 '18 at 17:15

0

addObserver returns an observer object. You are ignoring this and not retaining it. Therefore it goes out of scope and dies and the observation ends.

answered Dec 24 '18 at 17:15

matt

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Imho that's not the case. Although it would definitely be better to keep a reference to the observer object for unregistering at a later point. – André Slotta Dec 25 '18 at 14:40
I think Matt is actually right. The observer isn't the object you pass in. It's actually a new object that's created and returned -- I might be mistaken but I'm pretty sure I read about this recently. This is a different addObserver method, it functions a bit differently. – Eman Harout Dec 25 '18 at 23:50
I added `var avPlayerObserver: NSObjectProtocol?` to the class properties and changed my code to have `avPlayerObserver = NotificationCenter.default.addObserver( // ...` but the observer still seems to be gone after coming back from the modal. Was this your suggestion or did I misunderstand? – wizplum Dec 28 '18 at 18:07
Well, maybe you need to tell us more about what “the observer still seems to be gone” means. Can you provide a clear reproducible example? – matt Dec 28 '18 at 18:29

NotificationCenter observer clearing after presenting modal

1 Answers1