Pausing timer when app is in background state Swift - ios

Question

My ViewController.swift
func startTimer() {
timer = NSTimer().scheduleTimerWithTimerInvterval(1.0,target: self,selctor: Selector("couting"),userinfo: nil, repeats: true)
}
func pauseTimer() {
timer.invalidate()
println("pausing timer")
}
and this is appDelegate.swift
func applicateWillResignActive(application: UIApplication) {
viewController().pauseTimer()
println("closing app")
}
It is printing pausing timer and closing app but when I open again I see it never paused. How do I do it correctly?

Answer 1

You have to set an observer listening to when the application did enter background. Add the below line in your ViewController's viewDidLoad() method.
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("myObserverMethod:"), name:UIApplicationDidEnterBackgroundNotification, object: nil)
Add the below function to receive the notification.
func myObserverMethod(notification : NSNotification) {
println("Observer method called")
//You may call your action method here, when the application did enter background.
//ie., self.pauseTimer() in your case.
}
Happy Coding !!!

Answer 2

Updated Answer for Swift 5:
NotificationCenter.default.addObserver
(self,
selector: #selector(myObserverMethod),
name:UIApplication.didEnterBackgroundNotification, object: nil)
#objc func myObserverMethod() {
print("Write Your Code Here")
}

Answer 3

Accepted answer by #Suresh in Swift 3
Set an observer listening to when the application did enter background in your ViewController's viewDidLoad() method.
NotificationCenter.default.addObserver(self, selector: #selector(myObserverMethod), name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
Add the below function to receive the notification.
func myObserverMethod(notification : NSNotification) {
print("Observer method called")
//You may call your action method here, when the application did enter background.
//ie., self.pauseTimer() in your case.
}

Answer 4

Updated Answer for Swift 4:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(myObserverMethod), name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
}
#objc func myObserverMethod() {
// Call your action method here, when the application did enter background.
}

Answer 5

You are creating a new object and calling pauseTimer() on it:
viewController().pauseTimer() // This line causes issue viewController(), creates a new instance
Instead of creating new object, either you should pass that instance to AppDelegate and call pauseTimer() on existing object or Listen for UIApplicationDidEnterBackgroundNotification notification in your view controller class and pause timer from there.