swift 3.0 实现短信验证码倒计时功能

class TCCountDown {private var countdownTimer: Timer?var codeBtn = UIButton()private var remainingSeconds: Int = 0 {  willSet {    codeBtn.setTitle("重新获取/(newValue)秒", for: .normal)    if newValue <= 0 {      codeBtn.setTitle("获取验证码", for: .normal)      isCounting = false    }  }}var isCounting = false {  willSet {    if newValue {      countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(self.updateTime), userInfo: nil, repeats: true)      remainingSeconds = 60      codeBtn.setTitleColor(BtnCodeColor, for: .normal)    } else {      countdownTimer?.invalidate()      countdownTimer = nil      codeBtn.setTitleColor(MainColor, for: .normal)    }    codeBtn.isEnabled = !newValue  }}@objc private func updateTime() {  remainingSeconds -= 1} } //调用方法 var countDown = TCCountDown()//实例化 countDown.isCounting = true//开启倒计时