Getting Exception: "Impossible to set up layout with view hierarchy unprepared for constraint"

Question

In my storyboard application I try to add extra UITextField to interface. But I get the exception that title says. I use SwiftAutoLayout library. Here is my 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..."     } } 

Answer 1

Try adding passwordTextField to its superview before binding any constraints to it.

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UPD (thanks @vmeyer and @MacMark): please notice that it's safer to add constraints not in viewDidLoad or viewWillAppear/viewDidAppear but in updateViewConstraints or viewWillLayoutSubviews since the view hierarchy might be unprepared for this operation.

Answer 2

I suggest you to not add constraints in viewDidLoad, because the view hierarchy is set, but not constraints. You should prefer updateViewConstraints or viewWillLayoutSubviews