parse xml return after a post method - windows-phone-7

Question

I use post to post parameter to server and get the result in string, how do I parse that result and bind it to listbox? It seems that (for some reason) I can't output the string to textblock or messagebox. For parse xml I use XDocument (which take stream in parameter)
My code following:
private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
string post = "track=love";
// post = HttpUtility.UrlEncode(post);
Console.WriteLine(post);
try
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
Stream postStream = request.EndGetRequestStream(asynchronousResult);
// Convert the string into a byte array.
byte[] postBytes = Encoding.UTF8.GetBytes(post);
// Write to the request stream.
postStream.Write(postBytes, 0, postBytes.Length);
postStream.Close();
// Start the asynchronous operation to get the response
request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private static void GetResponseCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
HttpStatusCode rcode = response.StatusCode;
Stream streamResponse = response.GetResponseStream();
StreamReader streamRead = new StreamReader(streamResponse);
//THIS ALWAYS RETURN "" VALUE, EXPECT TO RETURN XML STRING
string str = streamRead.ReadToEnd();
//Console.WriteLine(responseString);
// Close the stream object
streamResponse.Close();
streamRead.Close();
// Release the HttpWebResponse
response.Close();
}
and I want to use XDocument to parse the data like this:
XDocument xdoc = XDocument.Load(str);
var data = from query in xdoc.Descendants("tracks").Elements("item")
select new searchResult
{
artist = (string)query.Element("artist"),
album = (string)query.Element("album"),
track = (string)query.Element("track"),
// artistA = (string)query.Element("artists").Element("artist"),
};
listBox1.ItemsSource = data;
var data1 = from query in xdoc.Descendants("artists").Elements("item")
select new searchResult
{
artistA = (string)query.Element("artist"),
};
listBox2.ItemsSource = data1;