Swift Firebase Login Registration auth - swift

Question

So when I first the page up I've kept it simple 2 text fields (email & password) 1 lbl 2 buttons (login register). Initially when I started out testing it everything worked when there was a problem an alert would pop up and tell you the problem, or you would be segue to next page based on button press and auth being complete.
But now every time I open the app to run code deeper inside no matter what I type I can sign in with the wrong password, or sign in with a previous email address even though previously these would both present errors. I have rebuilt this page numerous times over the week and decided to also add a get photo function from the users profile page.
Whenever I run the app and press a button I get this in the console:
Warning: Attempt to present on whose view is not in the window hierarchy!
I figure this is the problem because there is an error with the registration but the user is allowed to continue regardless. I've looked it up googled it read all the documentation I can find and even messed about trying and failing to put in a task structure.
PS I moved away from error label to use alerts hoping they would force a stop in the code
#IBAction func registerBtn(_ sender: Any) {
if emailTextField.text! == "" || passwordTextField.text == "" {
displayAlert(title: "Error", message: "Please Enter Your EMail Address & Choose A Password")
} else {
if let email = emailTextField.text {
if let password = passwordTextField.text {
//Create User
Auth.auth().createUser(withEmail: email, password: password, completion: { (user, error) in
// Auth.auth().createUserAndRetrieveData(withEmail: email, password: password, completion: { (user, error) in
if error != nil {
self.displayAlert(title: "Error", message: error!.localizedDescription)
} else {
print("Registration Successful")
self.performSegue(withIdentifier: "registrationSegue", sender: nil)
}
self.login()
})
}
}
}
}

Answer 1

if error != nil {
// show your alert
}
You don’t need an else statement on authenticating your users. so delete that line
Also, if you’re presenting a view controller that’s supposed to be accessible by authenticated users.
Please try:
let HomePage = HomePageController() // Change this to your viewcontroller name
self.present(HomePage, animated: true, completion: nil)

Answer 2

swift 4 - Xcode 9.1
func signUP(){
Auth.auth().createUser(withEmail: emailIdTextField.text!, password: passworTextField.text!) { (user, error) in
print(user?.email)
}
}
func signIn(){
Auth.auth().signIn(withEmail: emailTextField.text!, password: passwordTextField.text!) { (user, error) in
print(user?.uid)
}
}

Answer 3

Swift 4.2
//creating user with email password authentication
Auth.auth().createUser(withEmail: emailTextfield.text!, password: passwordTextfield.text!) { (user, error) in
// completion handler
if error != nil {
print(error!)
} else {
//success
print("Registration Sucessful")
self.performSegue(withIdentifier: "goToChat", sender: self)
}
}