silverlight – HttpWebRequest.EndGetResponse在Windows Phone 7中抛出NotSupportedException异常

我的生产代码要复杂得多,但是我可以把它缩小到这个小代码：

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？