I am new to swift. I have added view to stackview using addArrangedSubview(). But I am not able to remove this view using removeArrangedSubview(). 
Even after removing arranged subView the view is still present
import Foundation
import UIKit
class render: UIViewController {
  let subview    = UIStackView()
  let mainview   = UIStackView()
  override func viewDidLoad() {
    super.viewDidLoad()
    self.mainviewlet()
    self.login()
  }
  func login() {
    let username = UITextField()
    // text field
    let button = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 40))
    //button
    // Adding to subview  
    subview.axis  = UILayoutConstraintAxis.vertical
    subview.distribution  = UIStackViewDistribution.equalSpacing
    subview.alignment = UIStackViewAlignment.center
    subview.spacing   = 16.0
    subview.addArrangedSubview(username)
    subview.addArrangedSubview(button)
    subview.translatesAutoresizingMaskIntoConstraints = false;
    // Adding subview to another stackview
    mainview.addArrangedSubview(subview)
    self.view.addSubview(mainview)
}
In another function I am removing the arranged subview
func signup(sender: UIButton!) {
    // Remove subview
    mainview.removeArrangedSubview(subview)
    subview.removeFromSuperview()
    let firstname = UITextField()
    firstname.textAlignment = NSTextAlignment.center
    firstname.textColor = UIColor.black
    firstname.frame = CGRect()
    firstname.frame.size.height = 30;
    firstname.text = "firstname"
    subview.addArrangedSubview(firstname)
    mainview.addArrangedSubview(subview)
    self.view.addSubview(mainview)
}
and my mainview is created as:
func mainviewlet {
  mainview.axis  = UILayoutConstraintAxis.vertical
  mainview.distribution  = UIStackViewDistribution.equalSpacing
  mainview.alignment = UIStackViewAlignment.center
  mainview.spacing   = 16.0
  mainview.translatesAutoresizingMaskIntoConstraints = false;
  self.view.addSubview(mainview)
}
I want the username & button to be deleted and add new field firstname to the subview. 
Am I doing it the right way ? How to delete subview ? Thanks for any help
 
     
     
     
     
     
    