Swift Timer.scheduledTimer() doesn't work

Question

I have two views in my swift app. I am performing a segue as below.

ViewController.swift -----------------> GameViewController.swift

When loading the GameViewController an value array also passed to GameViewController.swift from ViewController.swift

A timer should be initialized in GameViewController.swift

I tried to initialize a timer and call a method through it, but it doesn't work.

Followings are my code snippets.

ViewController.swift

func signIn(difficultyLvl:String){
    let username = usernameTxt.text
    let password = passwordTxt.text

    let url = URL(string: "http://192.168.1.106/speed/scoreBoardController.php?username="+username!+"&password="+password!+"&action=SIGNIN")

    let task = URLSession.shared.dataTask(with: url!) {(data, response, error) in
        let isPassed = String(data: data!, encoding:.utf8)?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)

        var gameViewControllerParams = [Int: [String: String]]()
        gameViewControllerParams[0] = ["userId" : isPassed!]
        gameViewControllerParams[1] = ["difficultyLvl" : difficultyLvl]

        if(isPassed != "null"){
            self.performSegue(withIdentifier: "gotoGame", sender: gameViewControllerParams)
        }
    }

    task.resume()
}

GameViewController.swift

class GameViewController: UIViewController {

    var gameViewControllerParams = [Int: [String: String]]()

    override func viewDidLoad() {
        super.viewDidLoad()

        let _ = Timer.scheduledTimer(timeInterval: 1.0, target:self, selector: #selector(self.setCalculationLs), userInfo:nil,repeats: true)
    }

    func setCalculationLs(){
        print("Timing")
    }

}

Answer 1

Swift 5.5

I was having this issue as well while working in a segued view controller. Since segues are executed as a background thread to the main thread (main view controller), running timer within the segued view controller won't work. So, that being known and also knowing timers don't work in background threads, I did some digging and found this Apple Documentation gem.

I added the following line right after my scheduled timer. The timer now works beautifully. It is just sending the timer to the main thread for execution.

myTimer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(self.updateWithTimer), userInfo: nil, repeats: true)
RunLoop.main.add(myTimer, forMode: .common)