swift ios - How to run function in ViewController from AppDelegate

Question

I am trying to run a function in certain ViewController using AppDelegate

func applicationDidBecomeActive(_ application: UIApplication) {
        ViewController().grabData()
}

But somehow the function does not seem to run at all when the app has become active after entering the app from the background.

The function looks like this

func grabData() {
        self._DATASERVICE_GET_STATS(completion: { (int) -> () in
            if int == 0 {
                print("Nothing")
            } else {
                print(int)

                for (_, data) in self.userDataArray.enumerated() {
                    let number = Double(data["wage"]!)
                    let x = number!/3600
                    let z = Double(x * Double(int))
                    self.money += z
                    let y = Double(round(1000*self.money)/1000)

                    self.checkInButtonLabel.text = "\(y) KR"
                }

                self.startCounting()
                self.workingStatus = 1
            }
        })
    }

And uses this var

var money: Double = 0.000

What have I missed?

Thanks!

Lascar

https://mcmap.net/q/332819/-detect-ios-app-entering-background – Slave

Is the certain view controller the initial view controller? If yes create a property in AppDelegate and assign the reference to that view controller to the property. If not – the other way round – in viewDidLoad() of the certain controller get the AppDelegate instance and assign the reference from there. Notification is most likely not needed. – Genic

Answer 1

ViewController().grabData() will create a new instance of the ViewController and call this function. Then.. as the view controller is not in use it will be garbage collected/removed from memory. You need to be calling this method on the actual view controller that is in use. Not a new instance of it.

The best option would be to listen for the UIApplicationDidBecomeActive notification that iOS provides.

NotificationCenter.default.addObserver(
    self,
    selector: #selector(grabData),
    name: NSNotification.Name.UIApplicationDidBecomeActive,
    object: nil)

make sure that you also remove the observer, this is usually done in a deinit method

deinit() {
    NotificationCenter.default.removeObserver(self)
} 

Lacasse

When should I remove the observer? – Lascar

deinit is usually the best place to remove it. this means that as the view controller is de-initialised (released from memory) then it removes itself as an observer. I used to do this in viewDidUnload but this has been deprecated now – Lacasse

Answer 2

I simply solved it like this:

func applicationDidBecomeActive(_ application: UIApplication) {
        let viewController = self.window?.rootViewController as! ViewController
        viewController.grabData()
}

Lascar

Don't do this. You should use the method posted by Scriptable – Slave

If sometime you will need to do things like reload a tableview I thing that your app will crash – Tresatrescha