class myClass: UIViewController {
  let mainview     = UIStackView()
  func createbutton() {
    let loadpageview = UIStackView()
    loadpageview.axis  = UILayoutConstraintAxis.vertical
    loadpageview.distribution  = UIStackViewDistribution.equalSpacing
    loadpageview.alignment = UIStackViewAlignment.center
    loadpageview.tag = 30
    loadpageview.spacing   = 16.0

    let buttn = UIButton()
    buttn.backgroundColor = .gray
    buttn.setTitle("testttt", for: .normal)
    buttn.frame.size.height = 30
    buttn.frame.size.width = 40
    buttn.addTarget(self, action: #selector(loginaction), for: .touchUpInside)

    loadpageview.addArrangedSubview(buttn)
    mainview.addArrangedSubview(loadpageview)
  }

  func mainviewlet() {
    mainview.axis  = UILayoutConstraintAxis.vertical
    mainview.distribution  = UIStackViewDistribution.equalSpacing
    mainview.alignment = UIStackViewAlignment.center
    mainview.spacing   = 16.0
    mainview.tag = 50

    mainview.translatesAutoresizingMaskIntoConstraints = false;
    self.view.addSubview(mainview)
  }
}

override func viewDidLoad() {
  super.viewDidLoad()
  self.mainviewlet()
  let pl = myClass()
  pl.createbutton()
}

override func viewDidLoad() {
  super.viewDidLoad()
  self.mainviewlet()
  self.createbutton()
}