title: Getting Exception: "Impossible to set up layout with view hierarchy unprepared for constraint"
body: <p>In my storyboard application I try to add extra <code>UITextField</code> to interface. But I get the exception that title says. I use <a href="https://github.com/indragiek/SwiftAutoLayout" rel="noreferrer">SwiftAutoLayout</a> library. Here is my code:</p>
  
  <pre><code>// MARK: - IBOutlets
  
  @IBOutlet weak var passwordTextField: UITextField!
  
  // MARK: - Properties
  
  let userIdTextField = UITextField()
  
  // MARK: - Lifecycle
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      self.passwordTextField.keyboardType = .NumberPad
  
      if getCurrentUserId() == nil {
          self.view.addSubview(userIdTextField)
          userIdTextField.setTranslatesAutoresizingMaskIntoConstraints(false)
          self.view.addConstraints([userIdTextField.al_leading == passwordTextField.al_leading,
              userIdTextField.al_trailing == passwordTextField.al_trailing,
              userIdTextField.al_top == passwordTextField.al_bottom + 8])
          userIdTextField.placeholder = "Enter User Id..."
      }
  }
  </code></pre>