1

这是我的代码:

namespace RequestApi
{
    public partial class MainPage : PhoneApplicationPage
    {
        private BackgroundWorker bw;
        private string ans;
        private JObject ansJson;
        private static ManualResetEvent allDone = new ManualResetEvent(false);
        // Constructor
        public MainPage()
        {
            InitializeComponent();

        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            string url = "http://192.168.0.43:8182/Account/SignIn";
            CreateRequest(url);

            userId.Text = ansJson.Value<int>("user_id").ToString();

        }


        private void CreateRequest(string url)
        {
            Debug.WriteLine("CreateRequest");
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
            req.ContentType = "application/json";
            req.Method = "POST";
            req.BeginGetRequestStream(new AsyncCallback(RequestCallback), req);
            allDone.WaitOne();
        }

        private  void RequestCallback(IAsyncResult aresult)
        {
            Debug.WriteLine("RequestCallback");
            HttpWebRequest req = (HttpWebRequest)aresult.AsyncState;
            Stream postStream = req.EndGetRequestStream(aresult);

            string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
            JObject json = JObject.Parse(obj);
            string s = JsonConvert.SerializeObject(json);
            byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);

            postStream.Write(postdata, 0, postdata.Length);
            postStream.Close();

            req.BeginGetResponse(new AsyncCallback(ResponseCallback), req);


        }

        private  void ResponseCallback(IAsyncResult aresult)
        {
            Debug.WriteLine("ResponseCallback");
            HttpWebRequest req = (HttpWebRequest)aresult.AsyncState;
            HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult);
            StreamReader reader = new StreamReader(resp.GetResponseStream());
            string response = reader.ReadToEnd();
            Debug.WriteLine(response);
            JObject responseJson = JObject.Parse(response);
            ansJson = responseJson;
            Debug.WriteLine("ansJson from responseCallback {0}", ansJson);
            reader.Close();
            resp.Close();
            allDone.Set();

        }
    }
}

当我调试应用程序时,它输入了 CreateRequest,然后输入了 RequestCallback,但随后它停止并且从不输入 ResponseCallback,而是尝试使用 userId.Text 分配 asnJson 值为 null,因为它没有输入 ResponseCallback。当我做错时,为什么它永远不会进入ResponseCallback?

4

2 回答 2

2

ManualResetEventtrue作为参数创建的,所以它已经发出信号开始了。这意味着allDone.Wait()调用将立即继续......所以CreateRequest将完成,您将立即尝试使用asnJson变量,正如您所说的那样null。我怀疑这会杀死应用程序 - 所以你永远没有机会得到回应。

现在,解决这个问题的方法是不要更改ManualResetEvent构造函数——无论如何,你不应该在 UI 线程中那样等待!你会阻止它,并且你已经删除了 Windows Phone 7 的全部要点,使一切从一开始都是异步的。

相反,您的回调应该在完成后使用调度程序回调到 UI 线程。请注意,如果请求出现任何问题,您还应该进行强大的错误处理。

于 2011-10-06T16:48:41.683 回答
1

与回答问题不完全相关,但答案块似乎是唯一适合我即将提出的建议的地方......您应该通过使用using块来围绕流进行适当的资源保护:

原始代码:

        Stream postStream = req.EndGetRequestStream(aresult);

        string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
        JObject json = JObject.Parse(obj);
        string s = JsonConvert.SerializeObject(json);
        byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);

        postStream.Write(postdata, 0, postdata.Length);
        postStream.Close();

新代码(还要确保您的编码对于请求是正确的:您的 Web 服务真的需要 UTF-16 吗?Web 服务器使用 UTF-8 (Encoding.UTF8) 更为常见):

        using (Stream postStream = req.EndGetRequestStream(aresult))
        {
            string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
            JObject json = JObject.Parse(obj);
            string s = JsonConvert.SerializeObject(json);
            byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);

            postStream.Write(postdata, 0, postdata.Length);
        }

原始代码:

        HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult);
        StreamReader reader = new StreamReader(resp.GetResponseStream());
        string response = reader.ReadToEnd();
        Debug.WriteLine(response);
        JObject responseJson = JObject.Parse(response);
        ansJson = responseJson;
        Debug.WriteLine("ansJson from responseCallback {0}", ansJson);
        reader.Close();
        resp.Close();

新代码:

        using (HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult))
        using (StreamReader reader = new StreamReader(resp.GetResponseStream()))
        {
            string response = reader.ReadToEnd();
            Debug.WriteLine(response);
            JObject responseJson = JObject.Parse(response);
            ansJson = responseJson;
            Debug.WriteLine("ansJson from responseCallback {0}", ansJson);
        }

我还建议用块包围你的reqandresp操作,try..catch以允许处理异常情况——否则它会冒泡到 AppDomain 的异常处理程序(也可以被 UnhandledException 事件挂钩)。

于 2011-10-06T17:52:07.933 回答