How to use container view programmatically - ios

Question

I created a ViewController, and I want to add in my ViewController a container view, here I set the container view inside my ViewController:
var containerView: UIView = {
let view = UIView()
view.translatesAutoresizingMaskIntoConstraints = false
view.backgroundColor = .red
return view
}()
func setUpViews() {
view.addSubview(containerView)
containerView.heightAnchor.constraint(equalToConstant: 300).isActive = true
containerView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
containerView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
containerView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
}
Here I set my instance of SecondViewController in the containerView:
override func viewDidLoad() {
super.viewDidLoad()
setUpViews()
let secondViewController = SecondViewController()
secondViewController.willMove(toParent: self)
containerView.addSubview(secondViewController.view)
self.addChild(secondViewController)
secondViewController.didMove(toParent: self)
}
In my SecondViewController, I declared label and a view, I set the label in the center of the view:
let label: UILabel = {
let label = UILabel()
label.text = "Hello!"
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(myView)
myView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
myView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
myView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
myView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
view.addSubview(label)
label.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
label.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}
That's what I see in my app, but I aspected to see a label in the center of the gray view.
It doesn't work like I aspected and I don't understand why.

Answer 1

You need to set the frame and/or constraints on the loaded view:
override func viewDidLoad() {
super.viewDidLoad()
setUpViews()
let secondViewController = SecondViewController()
secondViewController.willMove(toParent: self)
containerView.addSubview(secondViewController.view)
// set the frame
secondViewController.view.frame = containerView.bounds
// enable auto-sizing (for example, if the device is rotated)
secondViewController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
self.addChild(secondViewController)
secondViewController.didMove(toParent: self)
}