Create timer on a scroll view - ios

Question

How would I go about creating a timer function on a scroll view.
I have implemented a timer function that works correctly however due to the nature of a scrollView the view controller loads everytime the page is swiped & the timer gets reset.
How would I store the value of the timer from each page of the scrollView, so that it doesn't reset?
Below are my timer functions:
override func viewDidAppear(animated: Bool) {
// Start Timer Variables
startGame()
timerButtonStart()
}
Timer Functions
// Mark : Timer Functions
func startGame() {
let aSelector : Selector = "updateTime"
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: aSelector, userInfo: nil, repeats: true)
startTime = NSDate.timeIntervalSinceReferenceDate()
}
#IBAction func pauseTimer(sender: AnyObject) {
if timerPaused == false {
elapsedTime += startTimeDate.timeIntervalSinceNow
timer.invalidate()
timerPaused = true
} else {
let aSelector : Selector = "updateTime"
timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: aSelector, userInfo: nil, repeats: true)
startTimeDate = NSDate()
startTime = NSDate.timeIntervalSinceReferenceDate() + elapsedTime
timerPaused = false
}
}
func updateTime() {
var currentTime = NSDate.timeIntervalSinceReferenceDate()
//Find the difference between current time and start time.
var elapsedTime: NSTimeInterval = currentTime - startTime
//calculate the minutes in elapsed time.
let minutes = UInt8(elapsedTime / 60.0)
elapsedTime -= (NSTimeInterval(minutes) * 60)
//calculate the seconds in elapsed time.
let seconds = UInt8(elapsedTime)
elapsedTime -= NSTimeInterval(seconds)
//find out the fraction of milliseconds to be displayed.
let fraction = UInt8(elapsedTime * 100)
//add the leading zero for minutes, seconds and millseconds and store them as string constants
let strMinutes = minutes > 9 ? String(minutes):"0" + String(minutes)
let strSeconds = seconds > 9 ? String(seconds):"0" + String(seconds)
strMinutesGlobal = strMinutes
strSecondsGlobal = strSeconds
//concatenate minuets, seconds and milliseconds as assign it to the UILabel
timerLabel.text = "\(strMinutesGlobal!):\(strSecondsGlobal!)"
}
func timerButtonStart() {
var refreshButton = UIBarButtonItem(barButtonSystemItem: .Refresh, target: self, action: "timer") //Use a selector
navigationItem.leftBarButtonItem = refreshButton
navigationController!.navigationBar.barTintColor = UIColor.greenColor()
title = "Search result"
}

Answer 1

If you want to prevent that your NSTimer gets deallocated when switching view controllers, you could store the NSTimer instance in a separate singleton class instead of the view controller.
class MyTimer {
var sharedInstance = MyTimer()
var timer: NSTimer?
}
With this, you can access the NSTimer instance like this:
MyTimer.sharedInstance.timer

Answer 2

You can change your timer creation code to
if (timer == nil) {
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: aSelector, userInfo: nil, repeats: true)
}
and also when you invalidate your timer you will need to set it to nil. This will only recreate the timer if it doesn't already exist.