swift ios - How to run function in ViewController from AppDelegate

问题

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!

回答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)
} 

回答2:

I simply solved it like this:

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

来源：https://stackoverflow.com/questions/43831571/swift-ios-how-to-run-function-in-viewcontroller-from-appdelegate