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

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
}

Answer 2

now my func PanGestute is working incorrectly. the condition "outside the white container" is triggered all the time
#OmerTekbiyik ?
func addPanGestureRecognizare() {
let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePanGesture2(sender:)))
redContainer.addGestureRecognizer(pan)
}
#objc func handlePanGesture2(sender : UIPanGestureRecognizer) {
let fileView = sender.view!
switch sender.state {
case .began, .changed:
let translation = sender.translation(in: fileView)
fileView.center = CGPoint(x: fileView.center.x + translation.x, y: fileView.center.y + translation.y)
sender.setTranslation(CGPoint.zero, in: fileView)
case .ended:
if fileView.frame.intersects(whiteContainer.frame) {
print("in white container")
} else {
print("outside the white container")
UIView.animate(withDuration: 0.3, animations: { fileView.frame.origin = self.pointOrigin3!})
}
default:
break
}
}