UITabBar Lifecycle's methods are not fired from background start - ios

Question

I've have a UITabBar controller as main controller, with 2 tabs. Each tab is a NavigatorViewController with a UIViewController embedded.
If I open the application from background after a previous cold launch, none of the ViewWillAppear (UITabBarController, UIViewController) is fired.
How can I call the lifecycle of UITabBarChildren when user come from backgroud? (IE: From a notification)

Answer 1

That is not in the life cycle because the state of controllers is not changing during background mode or other application events.
You should observe for applicationWillEnterForegroundNotification
class VC: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Listen for application event somewhere early like `ViewDidLoad`
NotificationCenter.default.addObserver(self, selector: #selector(applicationWillEnterForegroundNotification), name: UIApplication.willEnterForegroundNotification, object: nil)
}
// Implement a function that you want to execute when event happen
#objc func applicationWillEnterForegroundNotification() {
// Do anything before application Enter Foreground
}
// Remove observer when the controller is going to remove to prevent further issues
deinit {
NotificationCenter.default.removeObserver(self)
}
}

Answer 2

When application comes from background non viewWillAppear/viewDidAppear is called for any active vc , you need to listen to app delegate like applicationWillEnterForegroundNotification
NotificationCenter.default.addObserver(self, selector: #selector(applicationWillEnterForegroundNotification), name: UIApplication.willEnterForegroundNotification, object: nil)
#objc func applicationWillEnterForegroundNotification(_ notification: NSNotification) {
print("To-Do")
}

Answer 3

You can add an observer to UIApplicationWillEnterForeground in your controllers.
Posted shortly before an app leaves the background state on its way to
becoming the active app.
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self,selector: #selector(self.appEnteredFromBackground(_:)),name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
}
#objc func appEnteredFromBackground(_ notification: NSNotification) {
print("From background")
}