Autolayout programmatically doesn't work

Question

I want to add programmatically an UIImageView to a view and add constraints to center it, vertically and horizontally. With the storyboard it\'s works but not programmatically.<

Answer 1

UPDATED TO SWIFT 3

I tested your code and the problem i found was that you missed this line:

transitionImageView.translatesAutoresizingMaskIntoConstraints = false

Also if you want your image size is 60x68 you need to add a couple of constraints for the width and height like this:

let constW = NSLayoutConstraint(item: transitionImageView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 60)

let constV = NSLayoutConstraint(item: transitionImageView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 68)

and add them to your UIImageView

transitionImageView.addConstraint(constW)
transitionImageView.addConstraint(constV)

Otherwise the UIImageView will be the UIImage size even if you assign CGSize (because setTranslatesAutoresizingMaskIntoConstraints(false) disables the CGSize you assigned).

So your viewDidLoad() method could be like this:

override func viewDidLoad() {
    super.viewDidLoad()
    let transitionImageView = UIImageView()
    transitionImageView.contentMode = UIViewContentMode.scaleToFill

    //Don't forget this line
    transitionImageView.translatesAutoresizingMaskIntoConstraints = false

    let transitionImage = UIImage(named: "SoProxyLogo60pt.jpg")
    transitionImageView.image = transitionImage
    self.view.addSubview(transitionImageView)

    // Position
    let transitionImageViewConstraintCenterX = NSLayoutConstraint(item: transitionImageView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0)
    transitionImageViewConstraintCenterX.identifier = "Transition Image View Constraint Center X"
    let transitionImageViewConstraintCenterY = NSLayoutConstraint(item: transitionImageView, attribute: .centerY, relatedBy: .equal, toItem: self.view, attribute: .centerY, multiplier: 1, constant: 0)
    transitionImageViewConstraintCenterY.identifier = "Transition Image View Constraint Center Y"

    let constW = NSLayoutConstraint(item: transitionImageView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 60)

    let constV = NSLayoutConstraint(item: transitionImageView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 68)

    self.view.addConstraint(transitionImageViewConstraintCenterX)
    self.view.addConstraint(transitionImageViewConstraintCenterY)
    transitionImageView.addConstraint(constW) //self.view.addConstraint(constW) also works
    transitionImageView.addConstraint(constV) //self.view.addConstraint(constV) also works
}