import UIKit

class FourVC: UIViewController {

    var label:UILabel = UILabel()

    var index : Int =

    var timer:Timer = Timer()

    override func viewDidLoad() {

        super.viewDidLoad()

        label = UILabel.init()

        label.frame = CGRect.init(x:,y:,width: ,height:)

        label.text = "计时器"

        label.textColor = UIColor.black

        self.view.addSubview(label)

        timer = Timer.scheduledTimer(timeInterval: , target: self, selector: #selector(createTimer), userInfo: nil, repeats: true)

        RunLoop.current.add(timer, forMode: RunLoopMode.commonModes)

        timer.fireDate = NSDate.distantFuture

        let endTimeBtn : UIButton = UIButton()

        endTimeBtn.frame = CGRect.init(x:,y:,width: ,height:)

        endTimeBtn.backgroundColor = UIColor.cyan

        endTimeBtn.setTitle("停止计时", for: UIControlState.normal)

        endTimeBtn.titleColor(for: UIControlState.normal)

        endTimeBtn.setTitleColor(UIColor.black, for: UIControlState.normal)

        endTimeBtn.addTarget(self, action: #selector(pressBtn1), for: UIControlEvents.touchUpInside)

        self.view.addSubview(endTimeBtn)

        let startTimeBtn : UIButton = UIButton()

        startTimeBtn.frame = CGRect.init(x:,y:,width: ,height:)

        startTimeBtn.backgroundColor = UIColor.cyan

        startTimeBtn.setTitle("开始计时", for: UIControlState.normal)

        startTimeBtn.titleColor(for: UIControlState.normal)

        startTimeBtn.setTitleColor(UIColor.black, for: UIControlState.normal)

        startTimeBtn.addTarget(self, action: #selector(pressBtn), for: UIControlEvents.touchUpInside)

        self.view.addSubview(startTimeBtn)

    }

    func pressBtn(){

        //开始计时，很远的过去

        timer.fireDate = NSDate.distantPast

    }

    func pressBtn1(){

        //关闭计时，很远的将来

        timer.fireDate = NSDate.distantFuture

    }

    func createTimer(){

        index +=

        label.text = "\(index)"

        if index ==  {

            //关闭计时器

            timer.fireDate = NSDate.distantFuture

            label.text = "倒计时停止\(index)"

        }

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // Dispose of any resources that can be recreated.

    }

}