在UIViewController，iOS Swift4.2，Xcode10.1中仅调用一次函数

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

Maybe this works. In your ViewController, add a static property:

    static var shouldPop = true

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if isBeingPresented || isMovingToParent {
         // Perform an action that will only be done once
             if (type(of: self).shouldPop) {
                 type(of: self).shouldPop = false
                 popView()
             }
        }
    }

Of course, depending on your setup, this won't work if you have more than one instance of this viewcontroller that should keep their own state on whether popView should be called or not.

Answer 2

You should call this in viewDidLoad method. It's called once per UIViewController life cycle. Documentation here .

Just like this:

override func viewDidLoad() {
    super.viewDidLoad()

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

If your way is pop view after you was once in view controller you could do like this:

    /// bool that help indicate your visit 
    var isViewControllerVisited = false 

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if isViewControllerVisited {
         // Perform an action that will only be done once
             popView()
        }

        //change it here
        isViewControllerVisited = true 
    }

Hope it's help!

Answer 3

As per the view controller's lifecycle, the viewDidLoad method only gets called once. so you should call your method only there.

Or you can try the following code:

var isScreenAppeared = false

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    if !isScreenAppeared {
         popView()
    }
    isScreenAppeared = true
}

Answer 4

Below code, try it..

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    UserDefaults.standard.set(false, forKey: "isPopOverVCPopped")

    if UserDefaults.standard.bool(forKey: "isPopOverVCPopped") == false {
        UserDefaults.standard.set(true, forKey: "isPopOverVCPopped")

        popView()
    }
}

Answer 5

For me I prefer to use lazy loading. This allow not to write any logic, just need to use Swift lazy var declaration. Something like this:

private lazy var viewDidAppearOnce: Bool = {
    popView()
}()

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    _ = viewDidAppearOnce
}

Answer 6

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

In App delegate, set bool value

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
     UserDefaults.standard.set(true, forKey: "showPop") // like so
     return true
}

Then, in first view controller try this,

  func hasLaunchPop() {
   let isshowPop: Bool = UserDefaults.standard.bool(forKey: "showPop")
        if isshowPop == true  {
            popView()
            UserDefaults.standard.set(false, forKey: "showPop")
        }
    }

then in viewdidload call like this,

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

So that PopView appears only once in your app when its launched and will never show up again.