swiftui不显示警报.onappear

Question

我对swiftui有一个了解性的问题。我想在Alamofire视图的开始处下载文件。如果无法下载，则应显示警报。不幸的是，我总是收到错误消息：“'AlertView'初始化程序的结果未使用”。

func download_file() {
    print("FILE GEDOWNLOAD")
    Alamofire.request("rubriken.json").responseJSON { response in
        print("Request: \(String(describing: response.request))")   // original url request
        print("Response: \(String(describing: response.response))") // http url response
        print("Result: \(response.result)")                         // response serialization result

        if let status = response.response?.statusCode
        {
            switch(status)
            {
            case 200:
                Alert(title: Text("Important message"), message: Text("Wear sunscreen"), dismissButton: .default(Text("Got it!")))
            case 500:
                print("The response failed")
            default:
                print("error with response status: \(status)")
            }
        }
     }
}

struct MainView: View {
    @EnvironmentObject var loginViewModel: LoginViewModel
    @State private var selection = 0

    var body: some View {
        NavigationView {
                List(0 ..< 30) { item in
                    Image(systemName: "photo")
                    VStack(alignment: .leading) {
                        Text("Apple Support")
                        Text("Passwort für die App")
                            .font(.subheadline)
                            .foregroundColor(.secondary)
                    }
                }.navigationBarItems(trailing:
                                Button(action: {
                                    self.loginViewModel.isLoggedIn = false
                                }) {
                                    Text("Sperren")
                                })
                .navigationBarTitle("Meine Passwörter")
        } .onAppear() {
            print("GESTARTET")
            download_file()
        }
    }
}

查询应在View .onappear的构造过程中进行。