UIView[Controller]Representable：SwiftUI 子视图显示在调试器中，但在运行时不显示

Question

因为ScrollView不提供设置 的功能contentOffset，所以我尝试使用UIScrollViewas UIViewRepresentable。附加的代码显示了视图和视图控制器的调用者和定义。

在模拟器或预览中运行代码时，只显示一个蓝色区域。调试显示器时，Text，按预期显示。

如果不知道原因 - 是因为我做错了什么，还是因为 Xcode 或 SwiftUI 中存在错误？

这是自定义滚动视图：

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.
    }
}

视图控制器：

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.
    }
}

来电者：

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()
    }
}

运行时和调试器中的显示：