Conditional loading of ViewControllers: Temporary display of wrong ViewController - ios

Question

I am trying to write a login process for my app. I have embedded a navigation controller to HomeViewController and set it as the initial ViewController. How can I fix it such that when a user enters the wrong credentials the HomeViewController will not be shown at all?
This is what it is doing:
Correct credentials entered
Display LoginViewController -> User inputs credentials -> Display HomeViewController
Wrong credentials entered
Display LoginViewController -> User inputs credentials -> Display HomeViewController -> Display LoginViewController
Code for LoginViewController (look at the last block of code)
func handlingAuthentication(notification: NSNotification) {
let dict = notification.object as! NSDictionary
if dict["error"]! as! Bool == true {
let errorMessage = dict["message"] as! String
//initialize Alert Controller
let alertController = UIAlertController(title: "Authentication error", message: errorMessage, preferredStyle: .Alert)
//Initialize Actions
let okAction = UIAlertAction(title: "Ok", style: .Default){
(action) -> Void in
self.dismissViewControllerAnimated(true, completion: nil)
}
//Add Actions
alertController.addAction(okAction)
//Present Alert Controller
self.presentViewController(alertController, animated: true, completion: nil)
}
else
{
NSUserDefaults.standardUserDefaults().setBool(true, forKey: "isUserLoggedIn")
NSUserDefaults.standardUserDefaults().synchronize()
self.dismissViewControllerAnimated(true, completion:nil)
}
}
Code for HomeViewController
override func viewDidAppear(animated: Bool) {
let isUserLoggedIn = NSUserDefaults.standardUserDefaults().boolForKey("isUserLoggedIn")
if(!isUserLoggedIn){
self.performSegueWithIdentifier("toLoginVC", sender: self)
}
}
UPDATE
I've tried placing the code block in ViewDidLoad but I am still getting the same issue (in fact now I'm stuck on the homePage)
override func viewDidLoad() {
super.viewDidLoad()
let isUserLoggedIn = NSUserDefaults.standardUserDefaults().boolForKey("isUserLoggedIn")
if(!isUserLoggedIn){
self.performSegueWithIdentifier("toLoginVC", sender: self)
}
usernameLabel.text = Data.sharedInstance.userName
getTaskDetails()
displayTask.dataSource = self
}

Answer 1

If the main view controlled decides and displays the login you will inevitable see it on screen because it's already in the process of displaying - so it shouldn't do it. You should have some other controller, perhaps a splash view controller, which decides to show either the login or the main view.
In your login view controller the alert OK button calls dismiss, this is the reason the login controller disappears and re-appears again (after showing the main controller for a short time).