SWIFTUI 2.0

这是 Xcode 12/iOS 14 (SwiftUI 2.0) 中可能的替代解决方案，当滚动控件位于滚动区域之外时，可以在同一场景中使用(因为 SwiftUI2 ScrollViewReader 只能使用 inside ScrollView)

Here is possible alternate solution in Xcode 12 / iOS 14 (SwiftUI 2.0) that can be used in same scenario when controls for scrolling is outside of scrolling area (because SwiftUI2 ScrollViewReader can be used only inside ScrollView)

注意:行内容设计不在考虑范围内

使用 Xcode 12b/iOS 14 测试

Tested with Xcode 12b / iOS 14

class ScrollToModel: ObservableObject {
    enum Action {
        case end
        case top
    }
    @Published var direction: Action? = nil
}

struct ContentView: View {
    @StateObject var vm = ScrollToModel()

    let items = (0..<200).map { $0 }
    var body: some View {
        VStack {
            HStack {
                Button(action: { vm.direction = .top }) { // < here
                    Image(systemName: "arrow.up.to.line")
                      .padding(.horizontal)
                }
                Button(action: { vm.direction = .end }) { // << here
                    Image(systemName: "arrow.down.to.line")
                      .padding(.horizontal)
                }
            }
            Divider()
            
            ScrollViewReader { sp in
                ScrollView {
               
                    LazyVStack {
                        ForEach(items, id: .self) { item in
                            VStack(alignment: .leading) {
                                Text("Item (item)").id(item)
                                Divider()
                            }.frame(maxWidth: .infinity).padding(.horizontal)
                        }
                    }.onReceive(vm.$direction) { action in
                        guard !items.isEmpty else { return }
                        withAnimation {
                            switch action {
                                case .top:
                                    sp.scrollTo(items.first!, anchor: .top)
                                case .end:
                                    sp.scrollTo(items.last!, anchor: .bottom)
                                default:
                                    return
                            }
                        }
                    }
                }
            }
        }
    }
}

SWIFTUI 1.0+

这是一种有效的方法的简化变体，看起来很合适，并且需要几个屏幕代码.

Here is simplified variant of approach that works, looks appropriate, and takes a couple of screens code.

使用 Xcode 11.2+/iOS 13.2+ 测试(也使用 Xcode 12b/iOS 14)

Tested with Xcode 11.2+ / iOS 13.2+ (also with Xcode 12b / iOS 14)

使用演示:

struct ContentView: View {
    private let scrollingProxy = ListScrollingProxy() // proxy helper

    var body: some View {
        VStack {
            HStack {
                Button(action: { self.scrollingProxy.scrollTo(.top) }) { // < here
                    Image(systemName: "arrow.up.to.line")
                      .padding(.horizontal)
                }
                Button(action: { self.scrollingProxy.scrollTo(.end) }) { // << here
                    Image(systemName: "arrow.down.to.line")
                      .padding(.horizontal)
                }
            }
            Divider()
            List {
                ForEach(0 ..< 200) { i in
                    Text("Item (i)")
                        .background(
                           ListScrollingHelper(proxy: self.scrollingProxy) // injection
                        )
                }
            }
        }
    }
}

解决方案:

Light 视图可表示被注入到 List 中，可以访问 UIKit 的视图层次结构.由于 List 重用行，因此没有更多的值可以将行放入屏幕.

Light view representable being injected into List gives access to UIKit's view hierarchy. As List reuses rows there are no more values then fit rows into screen.

struct ListScrollingHelper: UIViewRepresentable {
    let proxy: ListScrollingProxy // reference type

    func makeUIView(context: Context) -> UIView {
        return UIView() // managed by SwiftUI, no overloads
    }

    func updateUIView(_ uiView: UIView, context: Context) {
        proxy.catchScrollView(for: uiView) // here UIView is in view hierarchy
    }
}

找到封闭的 UIScrollView(需要做一次)然后重定向所需的滚动到"的简单代理；对该存储的滚动视图的操作

Simple proxy that finds enclosing UIScrollView (needed to do once) and then redirects needed "scroll-to" actions to that stored scrollview

class ListScrollingProxy {
    enum Action {
        case end
        case top
        case point(point: CGPoint)     // << bonus !!
    }

    private var scrollView: UIScrollView?

    func catchScrollView(for view: UIView) {
        if nil == scrollView {
            scrollView = view.enclosingScrollView()
        }
    }

    func scrollTo(_ action: Action) {
        if let scroller = scrollView {
            var rect = CGRect(origin: .zero, size: CGSize(width: 1, height: 1))
            switch action {
                case .end:
                    rect.origin.y = scroller.contentSize.height +
                        scroller.contentInset.bottom + scroller.contentInset.top - 1
                case .point(let point):
                    rect.origin.y = point.y
                default: {
                    // default goes to top
                }()
            }
            scroller.scrollRectToVisible(rect, animated: true)
        }
    }
}

extension UIView {
    func enclosingScrollView() -> UIScrollView? {
        var next: UIView? = self
        repeat {
            next = next?.superview
            if let scrollview = next as? UIScrollView {
                return scrollview
            }
        } while next != nil
        return nil
    }
}