IOS swift countdown timer will not stop - ios

Question

I am attempting to make a countdown timer that counts down from 60 seconds and then stops when it gets to 0. But for the timer keeps going into negative seconds. Any advice is appreciated. Code:
#IBOutlet var timeCounter: UILabel!
var second = 60
var timer = NSTimer()
var timerRunning = true
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
setTimer()
timerCounting()
}
func setTimer(){
second -= 1
timeCounter.text = "\(second)"
}
func timerCounting(){
if(timerRunning == true){
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("setTimer"), userInfo: nil, repeats: true)
timerRunning = true
if second == 0 {
timerRunning = false
timer.invalidate()
}
}
}

Answer 1

You have to move the invalidation into the setTimer function since at its current location will never be triggered because timerCounting is only called once - in the beginning.
func setTimer(){
second -= 1
timeCounter.text = "\(second)"
if second == 0 {
timerRunning = false
timer.invalidate()
}
}

Answer 2

play with this in playground
import XCPlayground
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true
import Foundation
#objc class C:NSObject {
var timer: NSTimer?
var second = 5
func setTimer(){
if c.second < 0 {
print("the timer fires the last time here ...")
timer?.invalidate()
} else {
print(second)
second -= 1
}
}
}
let c = C()
func timerCounting(){
c.timer = NSTimer.scheduledTimerWithTimeInterval(1, target: c, selector: Selector("setTimer"), userInfo: nil, repeats: true)
}
timerCounting()