Pausing timer when app is in background state Swift

问题

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?

回答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 !!!

回答2:

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.

}

回答3:

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")
}

回答4:

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.

回答5:

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.
}

来源：https://stackoverflow.com/questions/27687240/pausing-timer-when-app-is-in-background-state-swift

标签

ios

swift

nstimer

appdelegate