How to force Swift to wait the previous code is finished?

Question

I just began learning Swift, I am working with an API behind, the problem is that : Swift don't wait my function finish therefore my last function appears like no code was done before .

import Foundation
import UIKit
import Alamofire
import SwiftyJSON

// Classes
class User {

    init(data: Any) {
        self.sex = JSON(data)["sex"].string!
        print(self.sex)
    }

    var id: Int = 1
    var online: Bool = false
    var picture: String = ""
    var sex: String = "Male"
}

// Fonctions
func getBackground(_ apiURL: String, completion : @escaping(_ :Any) -> Void) {
    // Requête API avec Alamofire + SwiftyJSON
    AF.request(apiURL, method: .get).validate().responseJSON { response in
        switch response.result {
        case .success(let value):
            let jsonData = JSON(value)
            completion(jsonData["results"])
        case .failure(let error):
            print(error)
        }

    }
}

// Requête de connexion
getBackground("https://x..me", completion: { response in
    let user = User(data: response)
})

print(String(user.id) + ": " + String(user.online!))

Screenshot here

I have this error: "Use of unresolved identifier 'user'", I guess that Swift don't get the fact that User was defined previously

All my work works perfectly with my API, the "self.sex" is set and showed when I build the code. But I'm still "locked" like I can't do nothing after this code because Swift don't want to wait.

I tried the function async and sync but then, all my next code has to be under a function...

Thanks in advance

Answer 1

There's no need to wait.

Put the print line – and the code which proceeds the user – in the completion closure

getBackground("https://a.clet.me", completion: { response in
    let user = User(data: response)
    print(String(user.id) + ": " + String(user.online!))
})

The error Use of unresolved identifier 'user' occurs because the local variable user is only visible inside the scope ( {} ) of its declaration.

Answer 2

So, this problem is all about variables life cycle.

// This happens first

getBackground("https://a.clet.me", completion: { response in
    let user = User(data: response)

    // This happens third, once the request has completed.

    // user exists here.
    // Only after this moment you should handle anything related to the user
})

// This happens second

// user DOESN'T exist here, swift will move on