在后台模式下锁定手机的停止时间

Question

我想在手机锁定时停止计时器，那么我该怎么做呢？在代码中，当他进入后台模式时，我设置了计时器，所以它可以工作，但我不知道如何让计时器在手机锁定时停止。有谁有主意吗？

var backgroundTaskIdentifier: UIBackgroundTaskIdentifier?

override func viewDidLoad() {
    super.viewDidLoad()


    backgroundTaskIdentifier = UIApplication.shared().beginBackgroundTask {
        UIApplication.shared().endBackgroundTask(self.backgroundTaskIdentifier!)

    }

    timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(LoangeController.cosumTime), userInfo: nil, repeats: true)
    startTime = NSDate.timeIntervalSinceReferenceDate()




}


func cosumTime() {

    let currentTime = NSDate.timeIntervalSinceReferenceDate()

    var elapsedTime: TimeInterval = currentTime - startTime

    let hours = UInt8(elapsedTime / 3600.0)

    elapsedTime -= (TimeInterval(hours) * 3600)

    let minutes = UInt8(elapsedTime / 60.0)

    elapsedTime -= (TimeInterval(minutes) * 60)

    let seconds = UInt8(elapsedTime)

    elapsedTime -= TimeInterval(seconds)


    //add the leading zero for minutes, seconds and millseconds and store them as string constants

    let strHours = String(format: "%02d", hours)
    let strMinutes = String(format: "%02d", minutes)
    let strSeconds = String(format: "%02d", seconds)

    let counttime =  "\(strHours): \(strMinutes): \(strSeconds)"

    timeconsum = counttime

    print("\(counttime)")


    if timeconsum == timeout {
        print("Remind TimeOut")
        let UUID = Foundation.UUID().uuidString

        Notification.addNotification(title: "TimeOut Put your Phone away", date: CurrentTime, uuid: UUID)

    }
}