I can't add subViews in UIScrollView - swift

Question

I'm trying add a subview to UIScrollView. I add scrollView, subView and set constraints bellow :
class ViewController: UIViewController {
let scrollView : UIScrollView = {
let scrollView = UIScrollView()
scrollView.backgroundColor = .yellow
scrollView.translatesAutoresizingMaskIntoConstraints = false
scrollView.alwaysBounceVertical = true
return scrollView
}()
let catImageView : UIImageView = {
let img = UIImageView()
img.translatesAutoresizingMaskIntoConstraints = false
img.backgroundColor = .white
return img
}()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
view.addSubview(scrollView)
scrollView.frame = self.view.bounds
scrollView.contentSize = CGSize(width: self.view.frame.width, height: 1000)
scrollView.addSubview(catImageView)
catImageView.centerXAnchor.constraint(equalTo: self.scrollView.centerXAnchor).isActive = true
catImageView.centerYAnchor.constraint(equalTo: self.scrollView.centerYAnchor).isActive = true
catImageView.widthAnchor.constraint(equalToConstant: 200).isActive = true
catImageView.heightAnchor.constraint(equalToConstant: 100).isActive = true
}
I builded and scrollView and subiew are disappear. I don't know why...
Then I trying add subview another way like this :
view.addSubview(catImageView)
catImageView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
catImageView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
catImageView.widthAnchor.constraint(equalToConstant: 200).isActive = true
catImageView.heightAnchor.constraint(equalToConstant: 100).isActive = true
It's still the same. Please explained to me why. Thank a lot

Answer 1

You should only set the translatesAutoresizingMaskIntoConstraints to false in case you are adding the constraints to the view. You've set the property on the scrollView to false, but used the frame, and not constraints. Remove the line:
scrollView.translatesAutoresizingMaskIntoConstraints = false // <- remove
and it should work.
Hope this helps! Good luck!