NSTimer with drawing barChart in Background - swift

Question

I'm using an NSTimer in an iOS App in background, which is saving some data every 30 seconds in an array. The app shows the last 10 values (values of 5 minutes) in a linechart.
My problem is to use the function of saving data into the array every 30 seconds also in background, when the app isn't on screen. I've written a lot of themes about this, but I don't understand it.
My timer is the following:
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: (#selector(ViewController.counting)), userInfo: nil, repeats: true)
func counting() {
timerCounter += 1 //Int
if timerCounter%30==0 {
arrayOfValues.append(...) //Appending the array
reloadLineChart() // reload chart
}
}
Could anyone show me how to solve this? I know, there must be something with the background-methods in the ViewController, but don't now what to type in.
I think there must be a function, which is counting in background and a function that is reloading the chart when I'm back in the app.

Answer 1

I might understand that you don't want to declare the counter in app delegate, for whatever reason you might have,although I would recommend it. However you can call the functions I mentioned, from the same class in which you have defined the counter. You would need to call it like this:
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(
self,
selector: "applicationWillResignActive:",
name: UIApplicationWillResignActiveNotification,
object: nil)
}
func applicationWillResignActive(notification: NSNotification) {
// stop your counter
}
Then do the same with the other function. Hope is clear.

Answer 2

In your app delegate you can use this method :
func applicationWillResignActive(application: UIApplication) {}
The code you add in this function will run right before your app goes in the background . Therefore you can write there the code to stop the counter.
Afterwards you need to use the following function to activate the counter again:
func applicationWillEnterForeground(application: UIApplication) {}
The code you write in this function will run when you come back to the app again. Hope it is clear enough.