HttpWebRequest.EndGetResponse抛出的Windows Phone 7 NotSupportedException异常

Question

在Silverlight,Windows Phone 7的项目我创建一个HttpWebRequest的,得到RequestStream,写的东西进入流,并得到响应,但我总是得到NotSupportedException异常:"System.Net.Browser.OHWRAsyncResult.AsyncWaitHandle抛出类型'System.NotSupportedException'的异常

我的生产代码要复杂得多,但我可以将其缩小到这一小段代码:

public class HttpUploadHelper
{
    private HttpWebRequest request;
    private RequestState state = new RequestState();

    public HttpUploadHelper(string url)
    {
        this.request = WebRequest.Create(url) as HttpWebRequest;
        state.Request = request;
    }

    public void Execute()
    {
        request.Method = "POST";
        this.request.BeginGetRequestStream(
            new AsyncCallback(BeginRequest), state);
    }

    private void BeginRequest(IAsyncResult ar)
    {
        Stream stream = state.Request.EndGetRequestStream(ar);
        state.Request.BeginGetResponse(
            new AsyncCallback(BeginResponse), state);
    }

    private void BeginResponse(IAsyncResult ar)
    {
        // BOOM: NotSupportedException was unhandled; 
        // {System.Net.Browser.OHWRAsyncResult}
        // AsyncWaitHandle = 'ar.AsyncWaitHandle' threw an 
        // exception of type 'System.NotSupportedException'
        HttpWebResponse response = state.Request.EndGetResponse(ar) as HttpWebResponse;
        Debug.WriteLine(response.StatusCode);
    }
}

public class RequestState
{
    public WebRequest Request;
}

}

有人知道这段代码有什么问题吗？

Answer 1

在NotSupportedException当请求流调用之前未关闭皆可抛EndGetResponse.当您尝试获取响应时,WebRequest流仍处于打开状态并将数据发送到服务器.由于stream实现了IDisposable接口,因此一个简单的解决方案是使用using块中的请求流来包装代码:

private void BeginRequest(IAsyncResult ar)
{
    using (Stream stream = request.EndGetRequestStream(ar))
    {
        //write to stream in here.
    }
    state.Request.BeginGetResponse(
        new AsyncCallback(BeginResponse), state);
}

在尝试从Web服务器获取响应之前,using块将确保关闭流.

Answer 2

问题在于您如何处理从 的回调中访问原始请求BeginGetResponse。

与其持有状态引用，不如使用以下命令获取对原始请求的引用：

var request = (HttpWebRequest)asynchronousResult.AsyncState;

看一下这个非常基本（但有效）的示例，该示例通过向网站发布电子邮件和密码凭据来实现登录。

public static string Email;

public static string Password;


private void LoginClick(object sender, RoutedEventArgs e)
{
    Email = enteredEmailAddress.Text.Trim().ToLower();

    Password = enteredPassword.Password;

    var request = (HttpWebRequest)WebRequest.Create(App.Config.ServerUris.Login);

    request.ContentType = "application/x-www-form-urlencoded";
    request.Method = "POST";
    request.BeginGetRequestStream(ReadCallback, request);
}

private void ReadCallback(IAsyncResult asynchronousResult)
{
    var request = (HttpWebRequest)asynchronousResult.AsyncState;

    using (var postStream = request.EndGetRequestStream(asynchronousResult))
    {
        using (var memStream = new MemoryStream())
        {
            var content = string.Format("Password={0}&Email={1}",
                                        HttpUtility.UrlEncode(Password), 
                                        HttpUtility.UrlEncode(Email));

            var bytes = System.Text.Encoding.UTF8.GetBytes(content);

            memStream.Write(bytes, 0, bytes.Length);

            memStream.Position = 0;
            var tempBuffer = new byte[memStream.Length];
            memStream.Read(tempBuffer, 0, tempBuffer.Length);

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

    request.BeginGetResponse(ResponseCallback, request);
}

private void ResponseCallback(IAsyncResult asynchronousResult)
{
    var request = (HttpWebRequest)asynchronousResult.AsyncState;

    using (var resp = (HttpWebResponse)request.EndGetResponse(asynchronousResult))
    {
        using (var streamResponse = resp.GetResponseStream())
        {
            using (var streamRead = new StreamReader(streamResponse))
            {
                string responseString = streamRead.ReadToEnd();

                // do something with responseString to check if login was successful
            }
        }
    }
}