How can I center a button on view programmatically - swift

Question

I am trying to center a Button onto the bottom of a view but it never appears. The only time it appears is when I uncomment takePhotoButton.frame. What is the proper way to do this?
import UIKit
import AVFoundation
class InputViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let photoPreviewImageView = UIImageView()
photoPreviewImageView.frame = view.bounds
photoPreviewImageView.backgroundColor = UIColor.green
view.addSubview(photoPreviewImageView)
let imageOfPhotoButton = UIImage(named: "smallcircle.circle.fill") as UIImage?
let takePhotoButton = UIButton(type: .custom) as UIButton
takePhotoButton.setImage(imageOfPhotoButton, for: .normal)
//takePhotoButton.frame = CGRect(x: 10, y: 10, width: 60, height: 60) // It will appear with this code however i took it away because im trying to center it at the bottom of the screen
takePhotoButton.center = view.center
photoPreviewImageView.addSubview(takePhotoButton)
}
}

Answer 1

Use constraint anchors. After you add the takePhotoButton set them the following way:
takePhotoButton.bottomAnchor.constraint(equalTo: photoPreviewImageView.bottomAnchor).isActive = true
takePhotoButton.centerXAnchor.constraint(equalTo: photoPreviewImageView.centerXAnchor).isActive = true
This will set make your button have the same bottom and center as it's container.

Answer 2

Good day,
you have to add constraint.
import UIKit
class ViewController: UIViewController {
var loginButton : UIButton = {
let button = UIButton(type: .system)
button.setTitle("Login", for: .normal)
button.translatesAutoresizingMaskIntoConstraints = false
button.backgroundColor = .red
button.tintColor = .white
return button
}()
override func viewDidLoad() {
super.viewDidLoad()
constraintsInit()
}
func constraintsInit(){
view.addSubview(loginButton)
NSLayoutConstraint.activate([
loginButton.centerYAnchor.constraint(equalTo: self.view.centerYAnchor),
loginButton.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
loginButton.heightAnchor.constraint(equalToConstant: 30),
loginButton.leadingAnchor.constraint(equalTo: self.view.leadingAnchor,constant: 30),
loginButton.trailingAnchor.constraint(equalTo: self.view.trailingAnchor,constant: -30),
])
}
}
on youtube you can find several people that explain how create the views, using only code.