add container to another container - problem with container.frame.origin

Question

I am testing pan Gesture Recognizer. I add a white Container to view and then add another red container to the white container.

When I am printing the whiteContainer.frame.orgin I get correct CGPoint numbers but when I print redContaner CGPoint numbers I get 0.0, 0.0

class ViewController6 : UIViewController {

let whiteContainer = UIView()
let redContainer = UIView()

var pointOrigin2: CGPoint?
var pointOrigin3: CGPoint?

override func viewDidLoad() {
    super.viewDidLoad()
    setupView()
}

override func viewDidLayoutSubviews() {
    
    pointOrigin2 = whiteContainer.frame.origin
    print(pointOrigin2!)
    pointOrigin3 = redContainer.frame.origin
    print(pointOrigin3!)

}
private func setupView() {
    view.backgroundColor = .black
    
    configureContainer()
    configureRedContainer()
    addPanGestureRecognizare()
}

func configureContainer() {
    view.addSubview(whiteContainer)
    whiteContainer.translatesAutoresizingMaskIntoConstraints = false
    
    whiteContainer.backgroundColor = .white
    
    NSLayoutConstraint.activate([
        whiteContainer.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        whiteContainer.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        whiteContainer.widthAnchor.constraint(equalToConstant: 200),
        whiteContainer.heightAnchor.constraint(equalToConstant: 200)
    ])
}
func configureRedContainer() {
    whiteContainer.addSubview(redContainer)
    redContainer.translatesAutoresizingMaskIntoConstraints = false
    
    redContainer.backgroundColor = .red
    
    NSLayoutConstraint.activate([
        redContainer.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        redContainer.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        redContainer.widthAnchor.constraint(equalToConstant: 50),
        redContainer.heightAnchor.constraint(equalToConstant: 50)
    ])
}

When I am adding red Container to view (not whiteContainer.addSubview(red Container) ) I get the correct CGPoint number of the white and red container.

Why ?

Answer 1

Viewcontroller hasn't any calculation for the frames for subviews is not in own view if you add in viewDidLoad. If you add a subview to ViewController's view , then yes ViewController makes calculation for that view but if you add subview to view's subview , it doesnt. Thats why you can see the whiteContainer frame is not zero and redContainer is zero.

To make this you should say 'view , you should calculation it'. Thats why you must use view.layoutIfNeeded() after the constraints settings .

This gonna fix your problem

 func configureRedContainer() {

    whiteContainer.addSubview(redContainer)

    redContainer.translatesAutoresizingMaskIntoConstraints = false
    
    redContainer.backgroundColor = .red
    
    NSLayoutConstraint.activate([
        redContainer.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        redContainer.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        redContainer.widthAnchor.constraint(equalToConstant: 50),
        redContainer.heightAnchor.constraint(equalToConstant: 50)
    ])
    view.layoutIfNeeded() // must add after setting constraints

}