How to call function only once in UIViewController?

Question

I have function call (pop view) in my 1st view controller which have to be called only once in app. Since then whenever I return back to 1st View controller the function need not to be called again.

func popView() {
        let popOverVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "popView") as! popView
        self.addChild(popOverVC)
        popOverVC.view.frame = self.view.frame
        self.view.addSubview(popOverVC.view)
        popOverVC.didMove(toParent: self)
    }

I have tried the following code and previous other sources in stack overflow, didn't work though..

 ///// Once Action in View Controller
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if self.isBeingPresented || self.isMovingToParent {
         // Perform an action that will only be done once
             popView()
        }
    }

Answer 1

If you want to call that PopView function only once in your App then try this,

 override func viewDidLoad() {
     super.viewDidLoad()
     showPopUp()
 }

func showPopUp() {
        let showPop: Bool = UserDefaults.standard.bool(forKey: "showPop")
        if showPop == false {
            // don't show ----Pop
        } else {
           openPop()
           UserDefaults.standard.set(false, forKey: "showPop")
        }
        
 }

This will call the pop up only once in app life cycle...