getting subview height to estimate another view height - ios

Question

Hi i want to get the subviews height to estimate the detailUIView heightAnchor. In the detailUIView i have 4 labels that layedout using auto constraints(programmatically) and i want to get the views height so i can estimate the detailUIView.In the function estimateCardHeight i am iterating all the subviews and trying to get the height of each subview and adding them but i am getting 0.0. Whats am i missing here i couldn't figure it out.
class ComicDetailViewController: UIViewController {
var comicNumber = Int()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.navigationItem.title = "Comic Number: \(comicNumber)"
}
let detailUIView = DetailComicUIView()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
// Do any additional setup after loading the view.
detailUIView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(detailUIView)
addConstraints()
print(estimateCardHeight())
}
public func configure(with viewModel: XKCDTableViewCellVM){
detailUIView.configure(with: viewModel)
comicNumber = viewModel.number
}
private func estimateCardHeight() -> CGFloat{
var allHeight : CGFloat = 0
for view in detailUIView.subviews{
allHeight += view.frame.origin.y
}
return allHeight
}
private func addConstraints(){
var constraints = [NSLayoutConstraint]()
constraints.append(detailUIView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor, constant: 10))
constraints.append(detailUIView.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: 20))
constraints.append(detailUIView.rightAnchor.constraint(equalTo: self.view.rightAnchor, constant: -20))
constraints.append(detailUIView.heightAnchor.constraint(equalToConstant: self.view.frame.height/3))
NSLayoutConstraint.activate(constraints)
}
}

Answer 1

you are missing view.layoutIfNeeded()
addConstraints()
view.layoutIfNeeded()
print(estimateCardHeight())
as apple's saying
Use this method to force the view to update its layout immediately. When using Auto Layout, the layout engine updates the position of views as needed to satisfy changes in constraints.
Lays out the subviews immediately, if layout updates are pending.
And I guess:
the way to estimate height,
private func estimateCardHeight() -> CGFloat{
var allHeight : CGFloat = 0
for view in detailUIView.subviews{
allHeight += view.frame.size.height
// allHeight += view.frame.origin.y
}
return allHeight
}

Answer 2

An other way to achieve it.
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
print(estimateCardHeight())
}
viewDidLayoutSubviews()
Called to notify the view controller that its view has just laid out its subviews.