Stopwatch app counter going too fast - ios

Question

I am just learning iOS and programming in general and I am making a very basic iOS stopwatch app. I got the stopwatch working however, when I press start more than once the timer begins to go faster so that it is no longer a second long (gif here). Also, my formatting seems to be off for the seconds part, if you have any suggestions there it would be appreciated. Here is my code:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var minuteLabel: UILabel!
#IBOutlet weak var secondLabel: UILabel!
var timer = NSTimer()
var second = 0
var minute = 0
func updateTime() {
do{
if second != 59
{
second++
secondLabel.text = ".\(second)"
}
else
{
second = 0
minute++
secondLabel.text = "." + String(format:"$%.2f", second)
if minute < 10
{
minuteLabel.text = "0\(minute)"
}
else
{
minuteLabel.text = String(format:"$%.2f", minute)
}
}
}
}
#IBAction func resetButton(sender: AnyObject) {
timer.invalidate()
second = 0
minute = 0
secondLabel.text = ".00"
minuteLabel.text = "00"
}
#IBAction func stopButton(sender: AnyObject) {
timer.invalidate()
}
#IBAction func startButton(sender: AnyObject) {
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
Thank you for your help!

Answer 1

You are not invalidating timer when startButton is called, so tapping "Start" multiple times is creating duplicate timers which call the same function, updateTime. Change startButton to look like this:
#IBAction func startButton(sender: AnyObject) {
if !timer.valid
{
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
}
For your second question about the formatting, you need to put a condition to check for the seconds being less than 10, similar to what you did with the minutes. You would put a 0 in front of the seconds. In updateTime:
if second < 10
{
second++
secondLabel.text = ".0\(second)"
}
else if second <= 59
{
second++
secondLabel.text = ".\(second)"
}
else
{
...
}
See NSTimer documentation for more information.

Answer 2

You can get the desired formatting by using "%02d" instead of %.2f. Using %.2f will ensure 2 digits after the decimal point which is not true in your case (you have both second and minute as integers). Also you can use get away with using one label (e.g., timerLabel) as shown below:
var second = 0
var minute = 0
func updateTime() {
let dFormat = "%02d"
second++
if second == 59{
minute++
second = 0
}
let s = "\String(format: dFormat, minute):\String(format: dFormat, second))"
timerLabel.text = s
}
Hope this helps!