您可以检查onAppear中是否显示了最新元素。

struct ContentView: View {
    @State var items = Array(1...30)

    var body: some View {
        List {
            ForEach(items, id: \.self) { item in
                Text("\(item)")
                .onAppear {
                    if let last == self.items.last {
                        print("last item")
                        self.items += last+1...last+30
                    }
                }
            }
        }
    }
}