如何在 windows phone 7 中的每个请求之前发送预请求

Question

我想在发送每个请求之前向我的服务器发送一个预请求。从该预请求中，我将从我的服务器接收令牌，然后我必须将该令牌添加到所有请求中。这就是过程。

我尝试了一些方法来实现这一点。但我面临一个问题。也就是说，当我尝试发送预请求时，它正在处理当前请求。这意味着两个请求并行进行。

我想先发送预请求并解析响应。在解析了预请求响应之后，我只想发送另一个请求。但是第一个请求不等待预请求响应。请让我在所有请求之前以任何方式发送预请求。

这是我的代码：

ViewModel:

`public class ListExampleViewModel
    {
        SecurityToken sToken = null;
        public ListExampleViewModel()
        {
            GlobalConstants.isGetToken = true;
            var listResults = REQ_RESP.postAndGetResponse((new ListService().GetList("xx","xxx")));

            listResults.Subscribe(x =>
            {
                Console.WriteLine("\n\n..................................2");
                Console.WriteLine("Received Response==>" + x);
            });
        }
    }`

常量 Class 用于请求和响应：

`public class REQ_RESP
    {
        private static string receivedAction = "";
        private static string receivedPostDate = "";


        public static IObservable<string> postAndGetResponse(String postData)
        {
            if (GlobalConstants.isGetToken)
            {
    //Pre Request for every reusest               
                receivedPostDate = postData;
                GlobalConstants.isGetToken = false;
                getServerTokenMethod();
                postData = receivedPostDate;
            }

            HttpWebRequest serviceRequest =
            (HttpWebRequest)WebRequest.Create(new Uri(Constants.SERVICE_URI));


            var fetchRequestStream =
                 Observable.FromAsyncPattern<Stream>(serviceRequest.BeginGetRequestStream,
                                                                 serviceRequest.EndGetRequestStream);
            var fetchResponse =
                Observable.FromAsyncPattern<WebResponse>(serviceRequest.BeginGetResponse,
                                                            serviceRequest.EndGetResponse);

            Func<Stream, IObservable<HttpWebResponse>> postDataAndFetchResponse = st =>
            {
                using (var writer = new StreamWriter(st) as StreamWriter)
                {
                    writer.Write(postData);
                    writer.Close();
                }
                return fetchResponse().Select(rp => (HttpWebResponse)rp);
            };

            Func<HttpWebResponse, IObservable<string>> fetchResult = rp =>
            {
                if (rp.StatusCode == HttpStatusCode.OK)
                {

                    using (var reader = new StreamReader(rp.GetResponseStream()))
                    {
                        string result = reader.ReadToEnd();
                        reader.Close();
                        rp.GetResponseStream().Close();
                        XDocument xdoc = XDocument.Parse(result);
                        Console.WriteLine(xdoc);
                        return Observable.Return<string>(result);
                    }
                }
                else
                {
                    var msg = "HttpStatusCode == " + rp.StatusCode.ToString();
                    var ex = new System.Net.WebException(msg,
                        WebExceptionStatus.ReceiveFailure);
                    return Observable.Throw<string>(ex);
                }

            };

            return
                from st in fetchRequestStream()
                from rp in postDataAndFetchResponse(st)
                from str in fetchResult(rp)
                select str;
        }

        public static void getServerTokenMethod()
        {
            SecurityToken token = new SecurityToken();

            var getTokenResults = REQ_RESP.postAndGetResponse((new ServerToken().GetServerToken()));

            getTokenResults.Subscribe(x =>
            {
                ServerToken serverToken = new ServerToken();
                ServiceModel sm = new ServiceModel();
    //Parsing Response
                serverToken = extract(x, sm);
                if (!(string.IsNullOrEmpty(sm.NetErrorCode)))
                {
        MessageBox.Show("Show Error Message");
                }
                else
                {
                    Console.WriteLine("\n\n..................................1");
                    Console.WriteLine("\n\nserverToken.token==>" + serverToken.token);
                    Console.WriteLine("\n\nserverToken.pk==>" + serverToken.pk);                   
                }
            },
            ex =>
            {
                MessageBox.Show("Exception = " + ex.Message);
            },
            () =>
            {
                Console.WriteLine("End of Process.. Releaseing all Resources used.");
            });
        }
    }`

Answer 1

这里有几个选项：

对于在 WP7 中使用 HttpClient (you also need Microsoft.Bcl.Async 的 Web 请求，您可以使用更简单的 async/await 模型替换 Reactive Extensions 模型。使用 HttpClient，您的代码最终将如下所示：

请求和响应：

        public static async Task<string> postAndGetResponse(String postData)
    {
        if (GlobalConstants.isGetToken)
        {
            //Pre Request for every reusest               
            await getServerTokenMethod();
        }

        var client = new HttpClient();
        var postMessage = new HttpRequestMessage(HttpMethod.Post, new Uri(Constants.SERVICE_URI));
        var postResult = await client.SendAsync(postMessage);

        var stringResult = await postResult.Content.ReadAsStringAsync();

        return stringResult;
    }

视图模型：

    public class ListExampleViewModel
{
    SecurityToken sToken = null;
    public ListExampleViewModel()
    {
        GetData();
    }

    public async void GetData()
    {
        GlobalConstants.isGetToken = true;
        var listResults = await REQ_RESP.postAndGetResponse("postData");
    }
}

另一种选择是，如果您想继续使用 Reactive Extensions，请查看 RX 的 Concat 方法。有了它，您可以链接令牌请求和实际的网络请求：

如何在 windows phone 7 中的每个请求之前发送预请求

How to send pre request before every request in windows phone 7

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