C# WP8 async HttpWebRequest Post with xml request message

Question

i've been reading here for quite a long time, but in this case i'm not getting any further. I'm rather new to Windows Phone development and facing the following problem.

I'm calling a webservice were I have to post a xml request message. I've got the code working in regular c# (see code below)

private static string WebRequestPostData(string url, string postData)
{
    System.Net.WebRequest req = System.Net.WebRequest.Create(url);

    req.ContentType = "text/xml";
    req.Method = "POST";

    byte[] bytes = System.Text.Encoding.ASCII.GetBytes(postData);
    req.ContentLength = bytes.Length;

    using (Stream os = req.GetRequestStream())
    {
        os.Write(bytes, 0, bytes.Length);
    }

    using (System.Net.WebResponse resp = req.GetResponse())
    {
        if (resp == null) return null;
            using (System.IO.StreamReader sr = new System.IO.StreamReader(resp.GetResponseStream()))
        {
            return sr.ReadToEnd().Trim();
        }
    }
}

But for Windows Phone (8) development it needs to be async. After searching the web, and trying the various samples given here I came to the following code:

private async void DoCallWS()
{
    string url = "<my_url>";

        // HTTP web request
    var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
    httpWebRequest.ContentType = "text/xml";
    httpWebRequest.Method = "POST";

    // Write the request Asynchronously 
    using (var stream = await Task.Factory.FromAsync<Stream>(httpWebRequest.BeginGetRequestStream,
                                                                 httpWebRequest.EndGetRequestStream, null))
    {
        string requestXml = "<my_request_xml>";

        // convert request to byte array
        byte[] requestAsBytes = Encoding.UTF8.GetBytes(requestXml);

        // Write the bytes to the stream
        await stream.WriteAsync(requestAsBytes , 0, requestAsBytes .Length);

        stream.Position = 0;
        using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
        {
            //return reader.ReadToEnd();

            string result = reader.ReadToEnd();
        }
    }
}

The string result has the value of my request xml message i'm trying to sent....

I'm aware that async void methodes are not preferred but i will fix that later.

I've also tried to following the solution as described by Matthias Shapiro ( http://matthiasshapiro.com/2012/12/10/window-8-win-phone-code-sharing-httpwebrequest-getresponseasync/ ) but that caused the code to crash

Please point me in the right direction :)

Thnx Frank

Answer 1

What you're doing is only writing to the request stream. You're missing the code which reads from the response.

The reason you're getting back your request xml is that you reset the request stream and read from that exact stream.

Your method should look as follows:

private async Task DoCallWSAsync()
{
   string url = "<my_url>";

   // HTTP web request
   var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
   httpWebRequest.ContentType = "text/xml";
   httpWebRequest.Method = "POST";

   // Write the request Asynchronously 
   using (var stream = await Task.Factory.FromAsync<Stream>(httpWebRequest.BeginGetRequestStream,
                                                             httpWebRequest.EndGetRequestStream, null))
   {
       string requestXml = "<my_request_xml>";

       // convert request to byte array
       byte[] requestAsBytes = Encoding.UTF8.GetBytes(requestXml);

       // Write the bytes to the stream
       await stream.WriteAsync(requestAsBytes , 0, requestAsBytes .Length);
    }

    using (WebResponse responseObject = await Task<WebResponse>.Factory.FromAsync(httpWebRequest.BeginGetResponse, httpWebRequest.EndGetResponse, httpWebRequest))
    {
        var responseStream = responseObject.GetResponseStream();
        var sr = new StreamReader(responseStream);
        string received = await sr.ReadToEndAsync();

        return received;
    }
}