WVC

class WelcomeViewController: UIViewController, SegueDelegate {
    @IBOutlet weak var signInButton: UIButton!
    @IBOutlet weak var signUpButton: UIButton!
    @IBOutlet weak var logoImageView: UIImageView!
    @IBOutlet weak var descriptionLabel: UILabel!

    var screen = CGRect()
    let signUpView = SignUpView.signUpView()
    let signInView = SignInView.signInView()

    var a = SignUpView()

    override func viewDidLoad() {
        super.viewDidLoad()
        a.segueDelegate = self
    }

    @IBAction func signUpButtonClicked(sender: AnyObject) {
        fallAnimation(self.signUpButton, secondButton: signInButton, xib: signUpView)
    }

    func fallAnimation(firstButton: UIButton, secondButton: UIButton, xib: UIView) {
        xib.frame.size.width = self.screen.width
        xib.frame.size.height = self.screen.height

        self.view.addSubview(xib)
    }

    func runSegue(identifier: String) {
        print("B")
        self.performSegueWithIdentifier(identifier, sender: self)
    }
}