Swift: Can't center UIView in Superview with NSLayoutConstraint - ios

Question

i'm trying to center a view in the parent view but its not centering as expected. Here is my code an a screenshot of the result.
emptyView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(emptyView)
let centerXConstraint = NSLayoutConstraint(item: emptyView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0)
let centerYConstraint = NSLayoutConstraint(item: emptyView, attribute: .centerY, relatedBy: .equal, toItem: self.view, attribute: .centerY, multiplier: 1, constant: 0)
self.view.addConstraints([centerXConstraint])
self.view.addConstraints([centerYConstraint])

Answer 1

Here is the code,
import UIKit
class ViewController: UIViewController
{
#IBOutlet weak var emptyView: UIView!
override func viewDidLoad()
{
super.viewDidLoad()
self.emptyView.translatesAutoresizingMaskIntoConstraints = false
let centerXConstraint = NSLayoutConstraint(item: emptyView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0)
let centerYConstraint = NSLayoutConstraint(item: emptyView, attribute: .centerY, relatedBy: .equal, toItem: self.view, attribute: .centerY, multiplier: 1, constant: 0)
let widthConstraint = NSLayoutConstraint(item: emptyView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100)
let heightConstraint = NSLayoutConstraint(item: emptyView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100)
self.view.addConstraints([centerXConstraint, centerYConstraint, widthConstraint, heightConstraint])
self.view.layoutIfNeeded()
}
}
If you are using label or button or any other view that have intrinsic size, there is no need for height and width constraints
ViewController Interface :
Output :

Answer 2

Try this code
emptyView.translatesAutoresizingMaskIntoConstraints = false
let widthConstraint = NSLayoutConstraint(item: emptyView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: emptyView.frame.size.width)
let heightConstraint = NSLayoutConstraint(item: emptyView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: emptyView.frame.size.height)
var constraints = NSLayoutConstraint.constraints(
withVisualFormat: "V:[superview]-(<=1)-[label]",
options: NSLayoutFormatOptions.alignAllCenterX,
metrics: nil,
views: ["superview":view, "label": emptyView])
view.addConstraints(constraints)
// Center vertically
constraints = NSLayoutConstraint.constraints(
withVisualFormat: "H:[superview]-(<=1)-[label]",
options: NSLayoutFormatOptions.alignAllCenterY,
metrics: nil,
views: ["superview":view, "label": emptyView])
view.addConstraints(constraints)
view.addConstraints([ widthConstraint, heightConstraint])