类型＆＃39;定时器的价值＆＃39;没有会员＆＃39;无效＆＃39;

Question

为什么我无法使计时器无效？我不断收到错误消息：

  

类型的定义＆＃39;定时器＆＃39;没有会员＆＃39;无效＆＃39;

有人可以指出我正确的方向吗？以下是我的代码。

var totalTimeInSec = Double()
var timer = Timer()
var timeInSec = 00.0
{
    didSet {
        if timeInSec <= 0 {
            timer.invalidate() // This is where the error occurs.
            startBtn.setTitle("Start", for: .normal)
        }
    }
}

func initialSettings() {
    timerSetting.addTarget(self, action: #selector(self.settingTimer(sender:)), for: UIControlEvents.valueChanged)
    //timerSetting.addTarget(self, action: #selector(CollectionViewController.collectionView(_:cellForItemAt:)), for: UIControlEvents.valueChanged)
}

func settingTimer(sender: UIDatePicker) {
    let timeFormat = DateComponentsFormatter()
    timeFormat.allowedUnits = [NSCalendar.Unit.second, NSCalendar.Unit.minute, NSCalendar.Unit.hour]
    timeFormat.unitsStyle = DateComponentsFormatter.UnitsStyle.abbreviated
    timerLabel?.text = timeFormat.string(from: sender.countDownDuration)
    timeInSec = timerSetting.countDownDuration
    timeInSec = totalTimeInSec
}

@IBAction func timerStart(_ sender: UIButton) {
    if sender.titleLabel?.text == "Start" {
        resetCounter()
        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(self.changeLabelText), userInfo: nil, repeats: true)
        startBtn.setTitle("Stop", for: .normal)
    } else {
        timer.invalidate()
        startBtn.setTitle("Start", for: .normal)
        showTimer.animate(fromAngle: showTimer.angle, toAngle: 0, duration: 0.5, completion: nil)
    }
}

之前我曾使用timer.invalidate()没有问题，但似乎无法弄清楚为什么会发生这种情况。