Segue

.swift

@IBAction func saveButtonClicked() {
        
        let user = User(username: self.usernameTextField.text!, password: self.passwordTextField.text!)
        
        let isSaved = self.dataAccess.saveUser(user)
        
        if isSaved {
            performSegue(withIdentifier: "LoginTableViewController", sender: self)
        } else {
            self.messageLabel.text = "User name is already taken"
        }
    }