终止应用后，快速继续计时器

如何解决终止应用后，快速继续计时器

我正在构建一个应用程序，用户可以在其中记录他们使用的时间。现在从理论上讲，它可以工作。问题是：有时用户会进入后台，甚至终止应用程序，但是当它重新启动时，计时器应该继续计数并显示自启动以来的时间。现在，当应用重新启用时，它从新的位置开始。

代码在这里

didFinishLaunching中的AppDelegate：

if HelperFunctions.isKeyPresentInUserDefaults(key: "startedTimer") == true {
        UserDefaults.standard.set(Int(NSDate().timeIntervalSince1970),forKey: "reenteredTime")
        
        let mainStoryboardIpad : UIStoryboard = UIStoryboard(name: "Main",bundle: nil)
        let initialViewControlleripad : UIViewController = mainStoryboardIpad.instantiateViewController(withIdentifier: "timerStarted") as UIViewController
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window?.rootViewController = initialViewControlleripad
        self.window?.makeKeyAndVisible()
    }
    
    return true
}

和计时器所在的ViewController：

override func viewDidLoad() {
    super.viewDidLoad()
    if HelperFunctions.isKeyPresentInUserDefaults(key: "startedTimer") == true {
        
        let timeNow = UserDefaults.standard.integer(forKey: "reenteredTime")
        let timeStarted = Int(UserDefaults.standard.string(forKey: "startedTime")!)
        let passedTime = timeNow - timeStarted!
        print(passedTime)
        timeLabel.text = timeString(time: TimeInterval(passedTime))
        
    } else {
        runTimer()
    }

}

func runTimer() {
    UserDefaults.standard.set(Int(NSDate().timeIntervalSince1970),forKey: "startedTimer")
    timer = Timer.scheduledTimer(timeInterval: 1,target: self,selector: #selector(ScanTimeLogViewController.updateTimer),userInfo: nil,repeats: true)
    RunLoop.current.add(timer,forMode: .common)
    
}

@objc func updateTimer() {
    seconds += 1     //This will decrement(count down)the seconds.
    timeLabel.text = timeString(time: TimeInterval(seconds))
}

func timeString(time:TimeInterval) -> String {
    let hours = Int(time) / 3600
    let minutes = Int(time) / 60 % 60
    let seconds = Int(time) % 60
    return String(format:"%02i:%02i:%02i",hours,minutes,seconds)
}