UIView[Controller]Representable: SwiftUI Subview is shown in Debugger, but not when run - uikit

Question

Because the ScrollView does not provide a function to set the contentOffset, I'm trying to use the UIScrollView as UIViewRepresentable. The attached code shows both, the caller and the definition of the view and the view controller.
When running the code in simulator or previews, just a blue area is shown. When debugging the display, the Text is shown, as expected.
If have no idea about the reason - is it because I'm doing something wrong, or because there's a bug in Xcode or SwiftUI?
Here the custom scroll view:
struct PositionableScrollView<Content>: UIViewRepresentable where Content: View {
var content: () -> Content
init(#ViewBuilder content: #escaping () -> Content) {
self.content = content
}
func makeUIView(context: UIViewRepresentableContext<PositionableScrollView<Content>>) -> UIScrollView {
let scrollViewVC = PositionableScrollViewVC<Content>(nibName: nil, bundle: nil)
scrollViewVC.add(content: content)
let control = scrollViewVC.scrollView
return control
}
func updateUIView(_ uiView: UIScrollView, context: UIViewRepresentableContext<PositionableScrollView<Content>>) {
// Do nothing at the moment.
}
}
The view controller:
final class PositionableScrollViewVC<Content>: UIViewController where Content: View {
var scrollView: UIScrollView = UIScrollView()
var contentView: UIView!
var contentVC: UIViewController!
override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
setup()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
setup()
}
func setup() {
self.view.addSubview(self.scrollView)
self.scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
self.scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
self.scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
self.scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
self.scrollView.translatesAutoresizingMaskIntoConstraints = false
}
override func viewDidLoad() {
super.viewDidLoad()
debugPrint("self:", self.frame())
debugPrint("self.view:", self.view!.frame)
debugPrint("self.view.subviews:", self.view.subviews)
// debugPrint("self.view.subviews[0]:", self.view.subviews[0])
// debugPrint("self.view.subviews[0].subviews:", self.view.subviews[0].subviews)
}
func add(#ViewBuilder content: #escaping () -> Content) {
self.contentVC = UIHostingController(rootView: content())
self.contentView = self.contentVC.view!
self.scrollView.addSubview(contentView)
self.contentView.leadingAnchor.constraint(equalTo: self.scrollView.leadingAnchor).isActive = true
self.contentView.trailingAnchor.constraint(equalTo: self.scrollView.trailingAnchor).isActive = true
self.contentView.topAnchor.constraint(equalTo: self.scrollView.topAnchor).isActive = true
self.contentView.bottomAnchor.constraint(equalTo: self.scrollView.bottomAnchor).isActive = true
self.contentView.translatesAutoresizingMaskIntoConstraints = false
self.contentView.widthAnchor.constraint(greaterThanOrEqualTo: self.scrollView.widthAnchor).isActive = true
}
}
extension PositionableScrollViewVC: UIViewControllerRepresentable {
func makeUIViewController(context: UIViewControllerRepresentableContext<PositionableScrollViewVC>) -> PositionableScrollViewVC {
let vc = PositionableScrollViewVC()
return vc
}
func updateUIViewController(_ uiViewController: PositionableScrollViewVC, context: UIViewControllerRepresentableContext<PositionableScrollViewVC>) {
// Do nothing at the moment.
}
}
The callers:
struct TimelineView: View {
#State private var posX: CGFloat = 0
var body: some View {
GeometryReader { geo in
VStack {
Text("\(self.posX) || \(geo.frame(in: .global).width)")
PositionableScrollView() {
VStack {
Spacer()
Text("Hallo")
.background(Color.yellow)
Spacer()
}
.frame(width: 1000, height: 200, alignment: .bottomLeading)
}
.background(Color.blue)
}
}
}
}
struct TimelineView_Previews: PreviewProvider {
static var previews: some View {
TimelineView()
}
}
The display, when run, and in debugger: