Setting a view controller's view's frame with constraints? - ios

Question

This app has no storyboard. This is the root view controller where ViewController2 (page2) is instantiated. ViewController2's view is given constraints (leading, top, width, height). The constraints appear to work great except when I create a UINavigationController in page2.
class ViewController0: UIViewController {
let scrollView = UIScrollView()
let page1 = ViewController1()
let page2 = ViewController2()
override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
return UIInterfaceOrientationMask.allButUpsideDown
}
override func loadView() {
setView()
addScrollView()
addToScrollView()
}
func setView() {
view = UIView()
}
func addScrollView() {
scrollView.bounces = false
scrollView.isPagingEnabled = true
scrollView.backgroundColor = UIColor.brown
scrollView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(scrollView)
scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
scrollView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1.0).isActive = true
scrollView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1.0).isActive = true
}
func addToScrollView() {
addChildViewController(page1)
page1.view.translatesAutoresizingMaskIntoConstraints = false
scrollView.addSubview(page1.view)
page1.didMove(toParentViewController: self)
page1.view.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
page1.view.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
page1.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1.0).isActive = true
page1.view.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1.0).isActive = true
page1.view.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true
addChildViewController(page2)
page2.view.translatesAutoresizingMaskIntoConstraints = false
scrollView.addSubview(page2.view)
page2.didMove(toParentViewController: self)
page2.view.leadingAnchor.constraint(equalTo: page1.view.trailingAnchor).isActive = true
page2.view.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
page2.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1.0).isActive = true
page2.view.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1.0).isActive = true
page2.view.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true
page2.view.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true
}
}
Because for the navigation controller to work properly on page2, I must explicitly set the view's frame, as seen below with view.frame = UIScreen.main.bounds even though I set it in ViewController0 using constraints. If I don't again set the view's frame like so (below), the bounds of the view extend to infinity and the constraints within page2 become useless.
class ViewController2: UIViewController {
var navigation = UINavigationController()
let navigationRoot = ViewController3()
override func loadView() {
setView()
addNavigation()
}
func setView() {
view = UIView()
view.frame = UIScreen.main.bounds
}
func addNavigation() {
self.addChildViewController(navigationRoot)
navigationRoot.didMove(toParentViewController: self)
navigation = UINavigationController(rootViewController: navigationRoot)
view.addSubview(navigation.view)
}
}
I was under the impression that when you use constraints, you can forego the frame property of views entirely. Did I not set up the constraints correctly? Or because this is purely programmatic I must, therefore, at times, explicitly set the frame of a view?