setting up a button without using storyboards in xcode swift - swift3

Question

I am experimenting not using storyboards and just writing the UI in code. I have the button attributes, i added to the subview to the viewDidLoad and also set up the constraints. I should be seeing a button in the middle of the screen.
class ViewController: UIViewController {
var setupButton: UIButton = {
let button = UIButton(type: .system)
button.backgroundColor = UIColor(r: 80, g: 101, b: 161, a: 256)
button.setTitle("Button", for: .normal)
button.setTitleColor(UIColor.white, for: .normal)
button.translatesAutoresizingMaskIntoConstraints = false
button.titleLabel?.font = UIFont.boldSystemFont(ofSize: 18)
return button
}()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
view.addSubview(setupButton)
coolButton()
}
func coolButton() {
setupButton.centerXAnchor.constraint(equalTo: view.centerXAnchor)
setupButton.centerYAnchor.constraint(equalTo: view.centerYAnchor)
setupButton.widthAnchor.constraint(equalTo: view.widthAnchor, constant: -24)
setupButton.heightAnchor.constraint(equalToConstant: 150)
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
extension UIColor {
convenience init(r: CGFloat, g: CGFloat, b: CGFloat, a: CGFloat) {
self.init(red: r/255, green: g/255, blue: b/255, alpha: a/255)
}
}

Answer 1

From NSLayoutConstraint docs:
Note that only active constraints affect the calculated layout.
For newly created constraints, the active property is NO by default.
You just have to set the isActive property to true for your constraints.
setupButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
setupButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
setupButton.widthAnchor.constraint(equalTo: view.widthAnchor, constant: -24).isActive = true
setupButton.heightAnchor.constraint(equalToConstant: 150).isActive = true