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I'm trying to retrieve data from an Asynchronous function of Firebase and then set it as the ViewController's user variable: 

    var user : User!

override func viewDidLoad() {
    super.viewDidLoad()
    collectionView.dataSource = self
    fetchUser()
}


func fetchUser(){

    Api.User.observeCurrentUser { (user) in
        self.user = user

    }

The problem is that within the brackets of the 'observeCurrentUser' method I can actually see the user retrieved correctly but outside them the it is not associated to the self.user and when I try to print it outside the brackets it's nil.

Being said this, I searched on the web and I found out that this is because it's an asynchronous function. How can I get the self.user equal to the user retrieved in the 'observeCurrentUser' function so that I can work on it in the ViewController?

The Api.User.observeCurrentUser function retrieves the currentUser. It's coded in this way: 

func observeCurrentUser(completion: @escaping (User)-> Void){

    guard let currentUser = Auth.auth().currentUser else {
        return
    }

    REF_USERS.child(currentUser.uid).observeSingleEvent(of: .value) { (snapshot) in
        if let dict = snapshot.value as? [String: Any]{
            let user = User.transformUser(dict: dict)
            completion(user)
        }
    }
}

Where REF_USERS it's the reference of all users in the Firebase-Database

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  • 1
    What are you trying to do here? What is this Api.User.? You can access the currently authenticated user anywhere in your app with this code let user = Auth.auth().currentUser - can you clarify what you're asking? Also, please review the following two guides on asking questions: How do I ask a good question? and How to create a Minimal, Complete, and Verifiable example Commented Nov 16, 2019 at 14:57
  • Thanks for the correction @Jay: basically Api.User is a class created by be that contains a method (observeCurrentuser) that retrieves the user and pass it as an argument of the closure. Commented Nov 16, 2019 at 15:36
  • ...and...? Can you clarify what the question is and why that's needed? What's the actual issue? Commented Nov 16, 2019 at 15:43
  • The problem is that when I try to print the currentuser inside the closure it exists, but when I try to do this outside it it doesn't. How can I set the var self.user (that is a the view controller's variable) with the user retrieved in the closure? Commented Nov 16, 2019 at 15:48
  • Do what you have to do inside the closure in fetchUser or – more cumbersome – add a completion handler. Commented Nov 16, 2019 at 16:09

1 Answer 1

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Outside the closure, the observe request hasn't completed. The correct approach is to do everything that you need to do with the retrieved user -- including updating the UI -- inside the closure.

func fetchUser(){
    Api.User.observeCurrentUser { (user) in
        self.user = user
        // alternatively, add this line to the user setter.  but for now...
        self.updateUIBecauseTheUserChanged()
    }
}

func updateUIBecauseTheUserChanged() {
    // change the UI, e.g. reloadData on the collection view
}
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2 Comments

I did what you said creating this function: func updateUIuserChanged(with user : User){ self.userNameLabel.text = user.username } and then passing the user data inside of the closure. but when I run the app it prints out this error : Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
I solved the problem, thanks everyone for the support. I implemented what you suggested me and it worked well. thanks

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