Child view controller's view ignores Auto Layout constraints - ios

Question

I would like to add child view controller to UINavigationController's view. I have hierarchy like this
NavigationController -> View(drawer) -> View(contentContainer) -> child view controller should be pinned to the contentContainer
But for some reason it ignores the constraints and I get weird results. Please see the screenshot, drawer is green, contentContainer is yellow and the child controller is placed almost outside of the screen and has frame with 0 height.
The critical code is inside the drawerContentController didSet and setupView method. Please note that I'm using SnapKit for constraints but the same problem was happening by setting the NSLayoutConstraints traditionally
class NavigationController: UINavigationController {
private var drawerHeightConstraint: Constraint!
fileprivate lazy var drawer = UIView()
private lazy var contentContainer = UIView()
var drawerContentController: UIViewController? {
didSet {
guard let new = drawerContentController else {
oldValue?.removeFromParent(animated: true)
return
}
if let old = oldValue {
old.removeFromParent(animated: true) { _ in
self.add(child: new, superview: self.contentContainer, animated: true, completion: nil)
}
} else {
add(child: new, superview: contentContainer, animated: true, completion: nil)
}
}
}
override func viewDidLoad() {
super.viewDidLoad()
setupView()
}
private func setupView() {
view.addSubview(drawer)
drawer.backgroundColor = .green
drawer.snp.makeConstraints { make in
make.leading.bottom.trailing.equalToSuperview()
drawerHeightConstraint = make.height.equalTo(360).constraint
}
let blur = UIBlurEffect(style: .default)
let visualView = UIVisualEffectView(effect: blur)
drawer.addSubview(visualView)
visualView.pinToSuperView()
contentContainer.backgroundColor = .yellow
drawer.addSubview(contentContainer)
contentContainer.snp.makeConstraints { make in
make.edges.equalTo(drawer.safeAreaLayoutGuide)
}
}
func add(child controller: UIViewController, superview: UIView? = nil, animated: Bool, completion: ((Bool) -> Void)? = nil) {
controller.willMove(toParent: self)
addChild(controller)
controller.view.alpha = 0
(superview ?? view).addSubview(controller.view)
controller.view.pinToSuperView()
UIView.animate(withDuration: animated ? 0.3 : 0, animations: {
controller.view.alpha = 1
}) { finished in
controller.didMove(toParent: self)
completion?(finished)
}
}
}
extension UIView {
func pinToSuperView() {
snp.makeConstraints { make in
make.edges.equalToSuperview()
}
}
}
When I add a simple UIView to the contentContainer it works as expected
var drawerContentController: UIViewController? {
didSet {
let v = UIView()
v.backgroundColor = .purple
contentContainer.addSubview(v)
v.pinToSuperView()
}
}

Answer 1

Okay, I "solved" the issue.
It seems that UINavigationController does not like having child view controllers added to it. As seen on the screenshots, when child controller is added the entire view hierarchy of navigation controller is broken. On the second screenshot, the table view controller (white view) is displayed correctly, but in the first case it is not even in the view hierarchy!
So the moral is, try to not add child view controllers directly to UINavigationController, in the end it is not a normal UIViewController and doesn't even have a normal UIView. I have added another UIViewController to act as a container for UINavigationController and added the child controller to it. It now works as expected.