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My ViewDidLoad method on a ViewController is called twice, but only in a particular scenario. There are two view controllers which I need to present, one if user isn't logged in and the second if the user is logged in. I am using storyboard and have set a navigation controller as initial view controller in it.

In my AppDelegate didFinishLaunchingWithOptions method I have populated ViewControllers array with the desired controller as below

let storyboard = UIStoryboard(name: "Main", bundle: nil)

let navigationController = storyboard.instantiateViewController(withIdentifier: "navController") as! UINavigationController

if UserDefaults.standard.object(forKey: USERID) != nil {

    viewController = storyboard.instantiateViewController(withIdentifier: "HomeVC_ID") as! HomeVC

} 

else {

    viewController = storyboard.instantiateViewController(withIdentifier: "LoginVC_ID") as! LoginVC

}

navigationController.viewControllers = [viewController] as! [UIViewController]

self.window?.rootViewController = navigationController

self.window?.makeKeyAndVisible()

ViewDidLoad method in HomeVC is called twice, whereas it's called just once for LoginVC.

I already tried searching through articles viewDidLoad is called twice and viewDidLoad getting called twice on rootViewController at launch but couldn't corner the issue.

When you create your navigation view controller from the storyboard, this already contains it's rootViewController (which must not to be confused with the rootViewController of the UIWindow). I guess this is your HomeVC (in the storyboard). So, the storyboard magic already creates HomeVC, and you do not have to create it manually in didFinishLaunchingWithOptions.

If you have specify the storyboard as your main interface in the project's/target's properties, you do not need any creational code in didFinishLaunchingWithOptions and just let the framework perform the magic.

If you want to do this programatically, then - in the storyboard - you should remove the navigation controller, and create it manually (not via instantiateViewController) in didFinishLaunchingWithOptions. You would also add the appropriate root view controller here (instantiated from the storyboard), maybe like this:

let storyboard = UIStoryboard(name: "Main", bundle: nil)



if UserDefaults.standard.object(forKey: USERID) != nil {

    viewController = storyboard.instantiateViewController(withIdentifier: "HomeVC_ID") as! HomeVC

} else {

    viewController = storyboard.instantiateViewController(withIdentifier: "LoginVC_ID") as! LoginVC

}

let navigationController = UINavigationController(rootViewController:viewController)

self.window?.rootViewController = navigationController

self.window?.makeKeyAndVisible()

I would recommend don't do any manual segue OR load view controller in app delegate. Use following piece of code in viewDidLoad of LoginView (hoping this is root view of your app always).

Use segue for login to homeview.

if UserDefaults.standard.object(forKey: USERID) != nil {

     self.performSegue(withIdentifier: "HomeViewIdentifier", sender: self)

}

Considering HomeViewIdentifier is a segueId for LoginView to HomeView.
Why I am suggesting this because you need to segue back to loginView when user logs out. In case you make homeView as rootview then where will you go in case of logout.