Styjun

After sending a POST request using alamofire to register a user in my app, I am attempting to create a User object from the returned user_id from my server. However, when I attempt to print some attributes of this user object directly after I initialize it, it works fine. However, when I try and print some attributes of it after the alamofire post request has finished executing, I am getting nil.

import UIKit
import Alamofire

class ViewController: UIViewController 
 var user: User!
 @IBOutlet weak var nameField: UITextField!
 @IBOutlet weak var emailField: UITextField!
 @IBOutlet weak var phone_number_field: UITextField!

 override func viewDidLoad() 
 super.viewDidLoad()
 // Do any additional setup after loading the view, typically from a nib.

 
 //MARK: Actions
 @IBAction func generateQR(_ sender: UIButton) 
 let name = nameField.text
 let email = emailField.text
 let phone_number = phone_number_field.text
 let params: Parameters = ["name": name!, "email": email!, "phone_number": phone_number!]
 AF.request("http://127.0.0.1:5000/register", method: .post, parameters: params, encoding: JSONEncoding.default).responseString response in
 switch response.result 
 case .success:
 let user_id = response.result.value
 self.user = User(name: name!, email: email!, phone_number: phone_number!, user_id: user_id!)
 print(self.user?.name) // <--This print statement works correctly -->
 case .failure:
 print("Error")
 
 
 print(self.user?.name) // <--This prints nil and in the debugger, self.user shows as nil--> 
 performSegue(withIdentifier: "qrSegue", sender: self)
 

 //END Actions

 override func prepare(for segue: UIStoryboardSegue, sender: Any?) 
 if segue.destination is QRCodeController 
 //Pass user object
 let qr_controller = segue.destination as? QRCodeController
 qr_controller?.user = self.user
 
 

Your service call is async. Read about sync vs async methods.

Medium

Ray Wenderlich

AF sent request to the server and codes below continues working. When your response will arrive then success or failure blocks start working.

So the user object is not assigned until the success block is running.

Here is solution:

 AF.request("http://127.0.0.1:5000/register", method: .post, parameters: params, encoding: JSONEncoding.default).responseString response in
 switch response.result 
 case .success:
 let user_id = response.result.value
 self.user = User(name: name!, email: email!, phone_number: phone_number!, user_id: user_id!)

 print(self.user?.name) // <--This print statement works correctly -->
 performSegue(withIdentifier: "qrSegue", sender: self)

 case .failure:
 print("Error")
 

And you can show loading in your page while pending response from request and hide it on success.