HttpWebRequest.EndGetResponse 在 Windows Phone 7 中引发 NotSupportedException

问题描述

在 Silverlight-Windows Phone 7 项目中，我正在创建一个 HttpWebRequest，获取 RequestStream，将一些内容写入 Stream 并尝试获取响应，但我总是收到 NotSupportedException:System.Net.Browser.OHWRAsyncResult.AsyncWaitHandle 抛出了‘System.NotSupportedException’类型的异常

in a Silverlight-Windows Phone 7-project I am creating an HttpWebRequest, get the RequestStream, write something into the Stream and try to get the response, but I always get a NotSupportedException:"System.Net.Browser.OHWRAsyncResult.AsyncWaitHandle threw an exception of type 'System.NotSupportedException'

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:

My production code is far more complicated, but I can narrow it down to this small piece of code:

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?

Does anybody know what is wrong with this code?

推荐答案

NotSupportedException 在调用 EndGetResponse 之前没有关闭请求流时，可以抛出 NotSupportedException.当您尝试获取响应时，WebRequest 流仍处于打开状态并向服务器发送数据.由于流实现了 IDisposable 接口，一个简单的解决方案是使用请求流将代码包装在 using 块中:

The NotSupportedException can be thrown when the request stream isn't closed before the call to EndGetResponse. The WebRequest stream is still open and sending data to the server when you're attempting to get the response. Since stream implements the IDisposable interface, a simple solution is to wrap your code using the request stream in a using block:

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

using 块将确保在您尝试从 Web 服务器获取响应之前关闭流.

The using block will ensure that the stream is closed before you attempt to get the response from the web server.

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