iOS 13 : Scroll view inside navigation controller won't go under the status bar

Question

我想制作一个可在 SwiftUI 中使用的自定义 ScrollView ，它允许我设置滚动位置。我进行了一半，遇到了 ScrollView 在滚动时无法在状态栏下正确流动的问题。

问题是这样的:

在进行测试以查看问题所在时，我制作了一个基于 Storyboard的比较项目，该项目根本没有代码，只是一个与我在代码中的结构完全相同的结构。结果看起来像这样，这是我想要实现的:

似乎 Root View Controller View 没有一直到达顶部，但我不明白为什么。所有其他自动滚动插入魔术都可以正常工作。

这是我的代码，您可以在 Xcode 11 中使用 SwiftUI 创建一个新项目并将其粘贴到 ContentView.swift 中。

import SwiftUI
import UIKit

class UIScrollableViewController: UIViewController {
    let scrollView = UIScrollView()
    let contentController: UIViewController

    init(contentController: UIViewController) {
        self.contentController = contentController

        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(scrollView)

        // Add child controller
        scrollView.addSubview(contentController.view)
        addChild(contentController)

        let contentView = contentController.view!

        // Constrain scroll view
        scrollView.translatesAutoresizingMaskIntoConstraints = false;
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0).isActive = true
        scrollView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = true

        // Constrain child view to scroll view
        contentView.translatesAutoresizingMaskIntoConstraints = false
        contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        contentView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true
        contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true

        // Constrain width of child view to width of self.view, NOT scroll view
        contentView.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
    }
}

class ScrollableNavigationController: UINavigationController, UINavigationBarDelegate {
}

struct ScrollableNavigationViewController<Content: View>: UIViewControllerRepresentable {
    typealias UIViewControllerType = ScrollableNavigationController

    let hostingController: UIHostingController<Content>
    let scrollableContainer: UIScrollableViewController!

    init(@ViewBuilder content: () -> Content) {
        hostingController = UIHostingController(rootView: content())
        scrollableContainer = UIScrollableViewController(contentController: hostingController)

        scrollableContainer.title = "Scrollable"
    }

    func makeUIViewController(context: UIViewControllerRepresentableContext<ScrollableNavigationViewController>) -> ScrollableNavigationController {
        let navigationController = ScrollableNavigationController(rootViewController: scrollableContainer)

        navigationController.navigationBar.prefersLargeTitles = true

        return navigationController
    }

    func updateUIViewController(_ navigationController: ScrollableNavigationController, context: UIViewControllerRepresentableContext<ScrollableNavigationViewController>) {
    }
}

struct ScrollableNavigationView<Content: View>: View {
    var content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    var body: some View {
        ScrollableNavigationViewController {
            content
        }
    }
}

// MARK: Test

struct BoxView: View {
    var colors: [Color] = [.red, .blue, .orange, .pink, .yellow]

    var body: some View {
        ForEach(0 ..< 20) { i in
            ZStack {
                Rectangle()
                    .fill(self.colors[i % 5])
                    .padding()
                    .frame(height: 130)
                Text("\(i)")
                    .font(.title)
            }
        }
    }
}

struct ContentView: View {
    var body: some View {
        ScrollableNavigationView {
            BoxView()
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Answer 1

问题似乎出在场景委托(delegate)上，它导致整个 View 层次结构被包裹在 UIHostingController 中，它具有嵌套的 SwiftUI Controller 似乎能够避免的嵌入魔法。为了证明这一点，我想出了一个稍微有点老套的解决方案。

替换这个:

window.rootViewController = UIHostingController(rootView: ContentView())

与:

window.rootViewController = MyHostingController(rootView: ContentView())

MyHostingController看起来像这样:

class MyHostingController<Content: View>: UIHostingController<Content> {
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        view.subviews[0].frame = UIScreen.main.bounds
    }
}

从 iOS 13.1 开始，您似乎真的应该只尝试在两层 UIKit 之间集成 SwiftUI，而不是相反。 SwiftUI 在其内部包含太多未记录的魔法。