Update label.text from another class - swift

Question

I have a view controller with a label ("titre") and a button.
class PresentationViewController: UIViewController, UIScrollViewDelegate,SKProductsRequestDelegate, SKRequestDelegate {
#IBOutlet weak var titre: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
let defaults = UserDefaults.standard
if !defaults.bool(forKey: "XXXXXX.\(GlobalVariables.sharedinstance.circuitselectionne!)"){
titre.text = "2,90€"
}
else {
titre.text = "Démarrer la visite ! "
}
When this button is triggered, a function in another class is launched.
In this function, we define the boolean of the variable checked in the initial viewController.
let defaults = UserDefaults.standard
defaults.set(true,forKey:"XXXXXX.\(nomtelechargementàajouter)")
But when it's done, titre.text is not updated in my Viewcontroller.
So how could I refresh the value of titre.text in the ViewController?
Another point is this function could be called in other ViewController.
Any idea?

Answer 1

You can use Notifications and observers to control your code behavior between your data and your controllers.
On the end of your function that define the boolean variable that you check in the viewDidload of your viewController post a notification like this :
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "VariableDefined"), object: nil)
With this you create a notification called VariableDefined (you can name it as you want). object parameter allows you to send data or whatever parameter you want with this notification.
Then, you have to set up a listener to listen to this notification. Who is interested on your boolean variable ? Your viewController.
Put a listener of this notification on your view controller like this :
let name = Notification.Name(rawValue: "VariableDefined")
NotificationCenter.default.addObserver(
self, selector: #selector(checkVariable),
name: name, object: nil)
With this you are defining a listener to the notification called VariableDefined and handle it with the method checkVariable.
Finally, on this handler you can update your label title :
func checkVariable() {
let defaults = UserDefaults.standard
if !defaults.bool(forKey: "XXXXXX.\
(GlobalVariables.sharedinstance.circuitselectionne!)"){
titre.text = "2,90€"
} else {
titre.text = "Démarrer la visite ! "
}
}
Hope it will help you. That's a way to communicate between models and view controllers.