Check App State (Swift 3)

ViewController.swift

override func viewDidLoad() {
        super.viewDidLoad()
        //Notify the selector function when UIApplicationWillResignActive
        NotificationCenter.default.addObserver(self, selector: #selector(appMovedToBackground), name: .UIApplicationWillResignActive, object: nil)
}

func appMovedToBackground() {
        //Optional Delay before doing any action
        //Waits 5 sec before checking app state
        DispatchQueue.main.asyncAfter(deadline: .now() + 5.0) {
            self.checkApplicationState()
        }
        print("App is now running in Background")
}
    
func checkApplicationState(){
        let state = UIApplication.shared.applicationState
        
        if state == .background {
            //Do Someting
            //Like
            performSegue(withIdentifier: "BackToMaster", sender: nil)
        }
        
        else if state == .active {
            print("Active")
        }
}