SwiftUI在滚动时检测底部

import SwiftUI

struct ContentView: View {
    @State private var scrollPosition: CGFloat = 0
    
    var body: some View {
        ScrollViewReader { scrollViewProxy in
            ScrollView {
                VStack {
                    ForEach(0..<100) { index in
                        Text("Item \(index)")
                            .frame(height: 50)
                    }
                }
                .onAppear {
                    scrollViewProxy.scrollTo(99, anchor: .bottom)
                }
                .onChange(of: scrollPosition) { newPosition in
                    if newPosition >= scrollViewProxy.contentSize.height - scrollViewProxy.height {
                        // 已滚动到底部，执行相应操作
                        print("已滚动到底部")
                    }
                }
                .background(
                    GeometryReader { geometry in
                        Color.clear
                            .preference(key: ScrollPositionKey.self, value: geometry.frame(in: .global).minY)
                    }
                    .onPreferenceChange(ScrollPositionKey.self) { value in
                        scrollPosition = value
                    }
                )
            }
        }
    }
}

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

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