Label with Timer not Stopping - swift

Question

I am creating a lap stopwatch, and I am having trouble stopping the timer when the "STOP" button is clicked. I am able to get the text to reset to 0, but the timer keeps running and if I hit start again the timer is running as if I never hit stop.
Timer code:
func goTimer()
{
if timer == nil {
timer = Timer.scheduledTimer(timeInterval : 0.1,
target : self,
selector :#selector(timerAction(_:)),
userInfo: nil, repeats: true);
}
}
func stopTimer()
{
if timer != nil {
timer!.invalidate()
timer = nil
}
}
func updateTimer() {
let intervalTotal = -Int(startDate.timeIntervalSinceNow)
let hours = intervalTotal / 3600
let minutes = intervalTotal / 60 % 60
let seconds = intervalTotal % 60
if startButton.currentTitle == "STOP" {
totalTime.text = String(format: "%02i:%02i:%02i", hours, minutes, seconds)
lapTime.text = String(format: "%02i:%02i:%02i", hours, minutes, seconds)
}
}
#objc func timerAction (_ timer : Timer) {
print("timerAction(_:)")
self.updateTimer()
}
#IBAction func startTimer(_ sender: Any) {
if startButton.currentTitle == "STOP" {
startButton.backgroundColor = UIColor.systemGreen
startButton.setTitle("START", for : .normal)
stopTimer()
lapTime.text = "00:00:00"
}
else if startButton.currentTitle == "START" {
startButton.backgroundColor = UIColor.systemRed
startButton.setTitle("STOP", for : .normal)
goTimer()
lapButton.isEnabled = true
lapButton.backgroundColor = UIColor.systemBlue
}
}

Answer 1

let intervalTotal = -Int(startDate.timeIntervalSinceNow)
I don't see you resetting that startDate in your stopTimer() function.
you have a variable
var startDate: Date = Date()
somewhere on top of your code. If its not a variable (if its let) change it to variable. You want to set this value when you start your timer. so
func goTimer() {
// Add this to set the date to when your function starts
startDate = Date()
....
}
That's because when you're setting the value in your label here
func updateTimer() {
let intervalTotal = -Int(startDate.timeIntervalSinceNow)
....
}
you're setting the value from startDate until now