Constraints for two UIStackView - one under the other - ios

Question

I working on "Hangman" app. On the top I want image, in middle textfield, and bottom couple UIStackView row for letters. Now I try to add constraints for only two UIStackView one under the other, but one is always behind other ie. not see.
This is image where you can se only second stack view (named: stacklView2), and the first i cant see. Why? What I doing wrong?
And this is code:
import UIKit
class ViewController: UIViewController {
var imageView: UIImageView!
var answerTextfield: UITextField!
override func loadView() {
view = UIView()
view.backgroundColor = .white
imageView = UIImageView()
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.contentMode = .scaleAspectFit
imageView.layer.borderWidth = 1
view.addSubview(imageView)
answerTextfield = UITextField()
answerTextfield.translatesAutoresizingMaskIntoConstraints = false
answerTextfield.textAlignment = .center
answerTextfield.isUserInteractionEnabled = false
answerTextfield.layer.borderWidth = 1
view.addSubview(answerTextfield)
let button1 = UIButton()
button1.backgroundColor = .red
let button2 = UIButton()
button2.backgroundColor = .blue
let stackView1 = UIStackView(arrangedSubviews: [button1, button2])
stackView1.translatesAutoresizingMaskIntoConstraints = false
stackView1.distribution = .fillEqually
stackView1.axis = .horizontal
view.addSubview(stackView1)
let stackView2 = UIStackView(arrangedSubviews: [button2, button1])
stackView2.translatesAutoresizingMaskIntoConstraints = false
stackView2.distribution = .fillEqually
stackView2.axis = .horizontal
view.addSubview(stackView2)
NSLayoutConstraint.activate([
imageView.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor, constant: 5),
imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
answerTextfield.topAnchor.constraint(equalTo: imageView.bottomAnchor, constant: 20),
answerTextfield.widthAnchor.constraint(equalTo: view.layoutMarginsGuide.widthAnchor, multiplier: 0.5),
answerTextfield.centerXAnchor.constraint(equalTo: view.centerXAnchor),
stackView1.topAnchor.constraint(equalTo: answerTextfield.bottomAnchor, constant: 20),
stackView1.widthAnchor.constraint(equalTo: view.layoutMarginsGuide.widthAnchor, multiplier: 1.0),
stackView1.centerXAnchor.constraint(equalTo: view.layoutMarginsGuide.centerXAnchor),
//stackView1.bottomAnchor.constraint(equalTo: stackView2.layoutMarginsGuide.topAnchor, constant: -5),
stackView2.topAnchor.constraint(equalTo: stackView1.bottomAnchor, constant: 20),
stackView2.widthAnchor.constraint(equalTo: view.layoutMarginsGuide.widthAnchor, multiplier: 1.0),
stackView2.centerXAnchor.constraint(equalTo: view.layoutMarginsGuide.centerXAnchor),
stackView2.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor, constant: -5),
])
}
override func viewDidLoad() {
super.viewDidLoad()
imageView.image = UIImage(named: "Hangman-0")
answerTextfield.text = "T E X T F I E L D"
setupNavigationBar()
}
func setupNavigationBar() {
let hintButton = UIButton(type: .infoLight)
hintButton.addTarget(self, action: #selector(hintTapped), for: .touchUpInside)
navigationItem.leftBarButtonItem = UIBarButtonItem(customView: hintButton)
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(newGameTapped))
}
#objc func hintTapped() {
print("Hint button tapped!")
}
#objc func newGameTapped() {
print("New Game button tapped!")
}
}

Answer 1

You use same objects button1 and button2 in both stacks
let stackView1 = UIStackView(arrangedSubviews: [button1, button2])
let stackView2 = UIStackView(arrangedSubviews: [button2, button1])
so it's added to stackView2 only you need to create 2 other different ones as a single element can be added to only 1 view