SwiftUI Scroll View scroll offset

ContentView.swift

import SwiftUI

struct OffsetPreferenceKey: PreferenceKey {
    typealias Value = CGFloat
    static var defaultValue: CGFloat = 0
    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
        value = nextValue()
    }
}

struct ContentView: View {
    @State var offset = CGFloat(-1)
    var body: some View {
        VStack {
            Spacer()
            ScrollView(.horizontal, showsIndicators: false) {
                ZStack() {
                    LazyHStack {
                        ForEach(0...24, id: \.self) { idx in
                            Text("\(idx)")
                                .background(.yellow)
                        }
                    }
                    GeometryReader { geo in
                        Color.clear.preference(key: OffsetPreferenceKey.self, value: geo.frame(in: .named("sv")).minX)
                    }
                }
            }
            .coordinateSpace(name: "sv")
            .onPreferenceChange(OffsetPreferenceKey.self) { offset in
                self.offset = offset
            }
            Spacer()
            Text("Offset: \(offset)")
            Spacer()
        }
    }
}

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