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..."
    }
}

In xcode 10 beta 5 release notes: The exception “Impossible to set up layout with view hierarchy unprepared for constraint.” has improved diagnostics. (42514606) — mustafa, Aug 14 '18 at 07:18

knuku · Answer 1 · 2017-05-21T11:05:05.163

86

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

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.

edited May 21 '17 at 11:05

answered Nov 19 '14 at 08:36

knuku

6,082
1
35
43

5

I had a similar crash but the view was created within the code. And indeed I was add constraints before adding the view. If your view is already in the storyboard, could you add the constraints directly there? – Kevin Delord Apr 26 '15 at 10:09

score 12 · Answer 2 · answered Feb 08 '16 at 09:25

12

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

answered Feb 08 '16 at 09:25

vmeyer

1,998
21
23

6

This answer is good since adding constraints in didLoad or will/DidAppear can crash the app due to view hierarchy unprepared for this. – MacMark Sep 14 '16 at 06:59

score 5 · Answer 3 · answered Nov 04 '19 at 11:53

5

Please add the view to superview before adding constraints for the view in superview.

superView?.addSubview(view) superView?.addConstraints([topConstraint,leftConstraint,bottomConstraint,rightConstraint])

answered Nov 04 '19 at 11:53

Aakash Gupta

184
3
9

score 1 · Answer 4 · answered Aug 01 '19 at 12:27

1

You are trying to adding constraint to view which is not added/created in current view hierarchy. First add view then apply constraint.

answered Aug 01 '19 at 12:27

Gurjinder Singh

9,221
1
66
58

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

4 Answers4

Linked