swift 3.0 短信验证码倒计时实现

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