如何响应查看生命周期事件：onAppear() 和 onDisappear() ？

struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack {
                NavigationLink(destination: DetailView()) {
                    Text("Hello World")
                }
            }
        }
        .onAppear {
            print("ContentView appeared!")
        }
        .onDisappear {
            print("ContentView disappeared!")
        }
    }
}

struct DetailView: View {
    var body: some View {
        VStack {
            Text("Second View")
        }
        .onAppear {
            print("DetailView appeared!")
        }
        .onDisappear {
            print("DetailView disappeared!")
        }
    }
}