How to properly activate constraints in swift

Question

I am trying to programmatically add a button view object to my scene for an iOS app written in swift. I am trying to follow the answer here https://stackoverflow.com/a/36263784

But I cannot see the button on the scene. I call this method from my viewDidLoad method.

    func buildLoginButton() -> UIButton
{
    let button = UIButton()
    button.backgroundColor = .greenColor()
    button.setTitle("Test Button", forState: .Normal)
    self.view.addSubview(button)

    let c1 = NSLayoutConstraint(item: button, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0)

    let c2 = NSLayoutConstraint(item: button, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0)

    button.widthAnchor.constraintEqualToAnchor(nil, constant: 200).active = true
    button.heightAnchor.constraintEqualToAnchor(nil, constant: 100).active = true

     NSLayoutConstraint.activateConstraints([c1, c2])
    view.bringSubviewToFront(button)

    return button
}

Do you get any warnings regarding ambiguous layout constraints in debug pane? — Ozgur Vatansever, Aug 28 '16 at 18:33
Have you ensured `buildLoginButton()` gets called? On the main thread? — BaseZen, Aug 28 '16 at 18:33

score 1 · Accepted Answer · answered Aug 28 '16 at 19:03

1

let button = UIButton()
self.view.addSubview(button)

Stop! You forgot to say this:

button.translatesAutoresizingMaskIntoConstraints = false`

You must say this on any view that you create, put into the interface, and try to apply constraints to.

answered Aug 28 '16 at 19:03

matt

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How to properly activate constraints in swift

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