swift 简单倒计时

import UIKit

class ViewController: UIViewController {

   

    var btn : UIButton!

    var leftTime:Int = 60

    var timer :Timer!

    

    override func viewDidLoad() {

        super.viewDidLoad()

        

        

        btn = UIButton.init(type: .system)

        btn.frame = CGRect.init(x: 100, y: 400, width: 100, height: 100)

        btn.setTitleColor(UIColor.red, for: .normal)

        btn.setTitleColor(UIColor.green, for: .disabled)

        btn.setTitle("开始", for: .normal)

      

        btn.clipsToBounds = true

        btn.layer.cornerRadius = 5.0

        btn.addTarget(self, action: #selector(startClicked), for: .touchUpInside)

        

        

        self.view.addSubview(btn)

           }

 

    func startClicked() {

        

       leftTime = 60

    btn.setTitle("重新开始计时(\(leftTime))", for: .disabled)

      self.btn.isEnabled = false

        //获取该计时器的剩余时间

        timer = Timer.scheduledTimer(timeInterval: TimeInterval(1), target: self, selector: #selector(tickDown), userInfo: nil, repeats: true)

    }

    

    func tickDown() {

        //将剩余时间减少1秒

        

        leftTime -= 1

        print(leftTime)

        //修改UIDatePicker的剩余时间

           btn.setTitle("重新开始计时(\(leftTime))", for: .disabled)

        //如果剩余时间小于等于0

        if leftTime <= 0 {

            

            //取消定时器

             timer.invalidate()

            self.btn.isEnabled = true

             btn.setTitle("重新开始计时", for: .normal)

            let alter = UIAlertView()

            alter.title = "时间到"

            alter.message = "时间到"

            alter.addButton(withTitle: "确定")

            alter.show()

     

        }

    }

}