Counter reset to zero after change of ViewController

Question

I've implemented a counter in my app, and it works. Then, when I change of ViewController (When i run my app), my counter reset to 0 automatically. I want my counter to continue while i'm using the app.

Thank's for your Help :)

import UIKit

class ViewController: UIViewController
{
    /// Label
    private var customLabel : UILabel?

    /// MAximum Count to which label will be Updated
    private var maxCount : Int?
    /// Count which is currently displayed in Label
    private var currentCount : Int?
    /// Timer To animate label text
    private var updateTimer : Timer?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        customLabel = UILabel()
        customLabel?.textColor = .white
        customLabel?.font = UIFont(name: "HelveticaNeue-Bold", size: 25)
        customLabel?.textAlignment = .center


        /// Add label to View
        addConstraints()

        /// Start Timer
        DispatchQueue.main.async {
            self.maxCount = 600
            self.currentCount = 1
            self.updateTimer = Timer.scheduledTimer(timeInterval: 0.2, target: self, selector: #selector(ViewController.updateLabel), userInfo: nil, repeats: true)
        }
    }

    @objc func updateLabel() {
        self.customLabel?.text = String(currentCount!)
        currentCount! += 1
        if currentCount! > maxCount! {
            /// Release All Values
            self.updateTimer?.invalidate()
            self.updateTimer = nil
            self.maxCount = nil
            self.currentCount = nil
        }
    }

    func addConstraints(){
        /// Add Required Constraints
        self.view.addSubview(customLabel!)
        customLabel?.translatesAutoresizingMaskIntoConstraints = false
        customLabel?.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: 195).isActive = true
        customLabel?.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -50).isActive = true
        customLabel?.heightAnchor.constraint(equalToConstant: 50).isActive = true
        customLabel?.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 310).isActive = true
    }
}

You can declare a global variable or you can use a struct to store the variable. Check my answer. — Keshu R., Dec 23 '19 at 12:38
Perhaps each time you create a new view controller (be careful - there may be a memory leak) and the counter starts over. I have tested your code with two ViewControllers (switched between them) - the counter continued to work. Therefore, the problem is the implementation of the life cycle of the view controller, and not the implementation of the counter — Vadim Nikolaev, Dec 23 '19 at 12:47
Thank's @VadimNikolaev . You're right, it's a ViewController issue. I've just seen that with some of my viewController the counter continue, but with some it reset to 0. How can i fix this problem ? — Alexis Decloedt, Dec 23 '19 at 12:51
@AlexisDecloedt to understand how to fix it - you need to look at the full implementation of creating issued view controller (the place where the view controller is created). FYI: using force unwrapping is a high risk of application crash, try a different option for setting variables (for example, e.g. predefined variables like `private let maxCount : Int = 600` and `private var currentCount : Int = 1` — Vadim Nikolaev, Dec 23 '19 at 13:01
@VadimNikolaev where can i find the exact place where the view controller was created ? (sorry i'm a beginner). I can't see any difference between my different ViewController :/ — Alexis Decloedt, Dec 23 '19 at 13:07
@AlexisDecloedt I guess you should debug this place (for finding the exact place). Unfortunately, not seeing the full implementation of the application, I can not predict — Vadim Nikolaev, Dec 23 '19 at 13:25

score 1 · Accepted Answer · answered Dec 23 '19 at 22:04

1

Declare these two var and let:

var defaults  = UserDefaults.standard
let countKey = "CountKey"

Add this line of code whenever you update your counter:

defaults.set(currentCount, forKey: countKey)

To get back your value instead, use:

defaults.integer(forKey: countKey)

answered Dec 23 '19 at 22:04

Federica Benacquista

835
11
25

Hi @Marybnq , thank's a lot for your help ! I'll try your solution right now. i'm a beginner and have many questions. How can i contact you for potential other questions ? – Alexis Decloedt Dec 23 '19 at 22:14
Is there any instant messaging on SO ? @Marybnq – Alexis Decloedt Dec 23 '19 at 22:18
No, if you have telegram you can contact me there, the user is the same I have on here – Federica Benacquista Dec 23 '19 at 22:18
I've download it but can't find you. My pseudo is @alexisddt , can you find me ? – Alexis Decloedt Dec 23 '19 at 22:25
I found you but cannot send you any message. Another solution perhaps ? :) @Marybnq – Alexis Decloedt Dec 23 '19 at 22:40

score 0 · Answer 2 · answered Dec 23 '19 at 12:30

0

What actually happening is that whenever you come back to your ViewController You are creating a new counter What you need to do is Declare your counter Outside viewDidLoad() but make sure that your ViewController is the root ViewController of your app that never gets deinitialised otherwise your app will crash.

answered Dec 23 '19 at 12:30

Jai Nijhawan

3
4

So you are saying only rootViewControllers can achieve this? – Keshu R. Dec 23 '19 at 12:37
To keep the track of time you should always keep the Timer instance in memory. You can also do this by making the timer in app delegate and clearing it after the app goes out of memory – Jai Nijhawan Dec 23 '19 at 12:48
Thank's guy. Where can i find my Root View Controller ? @JaiNijhawan – Alexis Decloedt Dec 23 '19 at 13:18
Root View Controller is referred to as the first ViewController or the first screen of your app after launch screen – Jai Nijhawan Dec 24 '19 at 06:42

score 0 · Answer 3 · answered Dec 23 '19 at 12:49

0

My recommendation would be implementing the Timer thing in your root controller which will not die until your app gets terminated like your Navigation Controller/Tab Controller, and keep updating the label whenever the 'ViewController' appears.

Thats how it will work even when the Controller is dead.

answered Dec 23 '19 at 12:49

Zeeshan Ahmed

834
8
13

Thank's @ZeeshanAhmed . Where can i find my root controller ? (Sorry i'm a beginner) – Alexis Decloedt Dec 23 '19 at 13:01
in your appdelegate.swift file you would be setting an initial controller. – Zeeshan Ahmed Dec 24 '19 at 11:14
1

check this question for root controller https://stackoverflow.com/questions/26753925/set-initial-viewcontroller-in-appdelegate-swift – Zeeshan Ahmed Dec 24 '19 at 11:16

score 0 · Answer 4 · answered Dec 23 '19 at 15:35

Your counter is actually part of your view controller which lives in memory, and when you restart your app (from Xcode I assume). It is removing your app from device memory, that's why you are losing your timer count.

Best thing you can do is saving you timer count to User Defaults (which saves it to disk), which means when you reopen your app you can get it from User Defaults and continue changing your current count

Counter reset to zero after change of ViewController

4 Answers4