HelloViewController.swift

class HelloViewController: UIViewController {
  let label = UILabel(frame: .zero)
    
  override func viewDidLoad() {
    super.viewDidLoad()
    label.text = "Hello world!"
    label.translatesAutoresizingMaskIntoConstraints = false
    label.font = UIFont.systemFont(ofSize: 16.0, weight: .medium)
    label.textColor = .black
    label.textAlignment = .center
    label.numberOfLines = 1
    label.adjustsFontSizeToFitWidth = true
    view.addSubview(label)
    setConstraintsForLabel(label)
  }
    
  func setConstraintsForLabel(_ constrainedLabel: UILabel) {
    guard view.subviews.contains(constrainedLabel) else { return }
    let constraints = [
      constrainedLabel.heightAnchor.constraint(equalToConstant: constrainedLabel.intrinsicContentSize.height),
      constrainedLabel.widthAnchor.constraint(equalTo: view.safeAreaLayoutGuide.widthAnchor, constant: -20.0),
      constrainedLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
      constrainedLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: -40.0)
    ]
    NSLayoutConstraint.activate(constraints)
  }
}