Swift UILabel is nil (error) when app goes in background

Question

I have some code that changes the text of a UILabel, it works fine when the app is run first time around but when I close it (app goes to background) and then I reopen it, the UILabel is nil and the text can't be set again.

The text is set to the UILabel in viewDidLoad() function and I call viewDidLoad() in applicationWillEnterForeground function to set the text to the UILabel again - that's when it crashes giving the error fatal error: unexpectedly found nil while unwrapping an Optional value. I debugged it and the nil found is the UILabel

Here is some of the code in AppDelegate.swift:

func applicationWillEnterForeground(application: UIApplication) { 
     ViewController().refresh() 
}

And in ViewController.swift:

func refresh() {
    self.viewDidLoad()
}

Do you have any ideas why the UILabel becomes nil when the app goes to background?

Answer 1

Rather than trying to hold a reference to your view controller from your app delegate, it is better to simply have your view controller subscribe to the foreground entry event -

In your viewDidLoad add the following

NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("enteringForeground:"),
  name: UIApplicationWillEnterForegroundNotification, object: nil)

The add a function to your ViewController

func enteringForeground(notification: NSNotification) {
   // Whatever you need to do to refresh UI
   // DO NOT CALL viewDidLoad
}

deinit {

   NSNotificationCenter.defaultCenter().removeObserver(self)

}