Swift NavigationBar Press "Back" to get values, why?

I am using some values to perform some calculations. For testing purposes I show in Label1 a value as string, since it is stored as a string and in Label2 I show a casted value as a Double since I need them at the end as doubles for my calculations.

The weird thing is, that when I access the ViewController the first time it doesn't show any values. But if I go back and klick on it again using the navigation controller it actually works. But I need the values right away cause my original intention is as I said, not showing some labels but rather making some calculations with it.

I made a little gif to show you what the problem is but I have problem with adding photos. Basically what happens is, that I click on the ViewController with the labels and nothing is showed. I go back and press again and the values will be showed in the labels.

Why is that and how can it be showed right away/ used for calculations right away

Thanks for the help. :)

class AHPfinalPreferencesViewController: UIViewController {

  var ahpPrios = [AHPPriorityStruct]()
    let decoder = JSONDecoder()

    @IBOutlet weak var label1: UILabel!
    @IBOutlet weak var label2: UILabel!
    
   
    let ajkpXc = globaLajkpXc
    let ajkpXijr = globaLajkpXijr

    let valueA = globaLajkpXc
    let valueB = Double(globaLajkpXijr)


 override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
        UserService.ahpPref(for: User.current) { (ahpPrios) in
                self.ahpPrios = ahpPrios
                print("This is our AHP PRIOS", ahpPrios)
                

                for ahpPrio in ahpPrios {
                  print(ahpPrio)
                }
              
                print("this is the global ajk. ", self.ajkpXc)
        }
         
            
     }
        
    
    override func viewDidLoad() {
        super.viewDidLoad()

// Mark: - Get Data
      
             label1.text = valueA
             label2.text = "\(String(describing: valueB))"

        
// MARK: - Set Values for calculation
        
//        setValues()
//        ahpCalculation()
        
    }
  }

Could it be because of the globalVariables? I know that it is not the right way to do it but for my purposes its absolutely "okay"

import Foundation
import FirebaseAuth.FIRUser
import FirebaseDatabase
import FirebaseUI
import FirebaseAuth
import CodableFirebase

var globaLajkpXc: String = String()
var globaLajkpXijr: String = String()
var globaLajkpXqpa: String = String()


struct UserService {

static func ahpPref(for user: User, completion: @escaping ([AHPPriorityStruct]) -> Void) {
       
        
        let ref = Database.database().reference().child("AHPRatings").child(user.uid)
        
        
                ref.observe(DataEventType.value, with: { snapshot in
                    guard let value = snapshot.value else { return }
                    do {
                        let ahpPrios = try FirebaseDecoder().decode(AHPPriorityStruct.self, from: value)
                        print(ahpPrios)
                        
                        
                        // MARK: - lets store the values in the actual constants :)
                        
                        let ajkpXc = ahpPrios.ajkpXc
                        let ajkpXijr = ahpPrios.ajkpXijr
                        let ajkpXqpa = ahpPrios.ajkpXqpa

                             globaLajkpXc = ajkpXc ?? "no Value"
                             globaLajkpXijr = ajkpXijr ?? "no Value"
                             globaLajkpXqpa = ajkpXqpa ?? "no Value"

} catch let error {
                        print(error)
                    }
                })
        
     
        
          }

  }  


  [1]: https://i.sstatic.net/VKxaE.png

You are calling UserService's ahpPref in your controller's viewWillAppear. BUT you are attempting to put your valueA (globaLajkpXc's value) to your label in your controller's viewDidLoad.

So what does that mean? Do you know which of these two controller's life cycle method gets called and when they do get called?

To solve your problem, have your label assigning value code

label1.text = globaLajkpXc

move in the completion block of your ahpPref (in the viewWillAppear).

Here's the Apple's documentation about the UIViewController's lifecycle: https://developer.apple.com/library/archive/referencelibrary/GettingStarted/DevelopiOSAppsSwift/WorkWithViewControllers.html

Also, below this line: globaLajkpXqpa = ajkpXqpa ?? "no Value"

add your completion call, like:

completion([ahpPrios]).

This should make my answer above work.