Making a Silverlight app getting data from Google app Engine

Recently I am interested in Silverlight2 and Google App Engine.
So I've made a simple Silvelight2 app getting data from a mod on Google App Engine.

I adopted REST Protocol in communication between Silverlight2 and App Engine.

Here is the Server-Side code written in Python,about which you don't have any other choice.

  #!-*- coding:utf-8 -*-
  from google.appengine.ext import webapp
  from google.appengine.ext.webapp.util import run_wsgi_app

  class MainPage(webapp.RequestHandler):
    def get(self):
      self.response.headers['Content-Type'] = 'text/xml'
      self.response.out.write('<?xml version="1.0" encoding="UTF-8" ?>')
      self.response.out.write('<Person>')
      self.response.out.write('<LastName>Jackson</LastName>')
      self.response.out.write('<FirstName>Michael</FirstName>')
      self.response.out.write('</Person>')

  application = webapp.WSGIApplication(
                                     [('/', MainPage)],
                                     debug=True)

  def main():
    run_wsgi_app(application)

  if __name__ == "__main__":
    main()

The code above simply returns XML format string.

XML Format:

  <?xml version="1.0" encoding="UTF-8" ?>
  <Person>
  <LastName>Jackson</LastName>
  <FirstName>Michael</FirstName>
  </Person>

Next is the Client-Side code.

Silverlight2 has XML Serialize API. With it you can Deserialize XML String to a C# Class insntance.

So I defined Person class in first that corresponds to the XML format.

Person.cs:

  public class Person
  {
     public String LastName { get; set; }
     public String FirstName { get; set; }
  }

The following code makes an Asynchronous http request.
WebRequest class in Silverlight doesn't have GetResponse() which is synchronous version of BeginGetResponse() existing in .NET Framework.

  private String _svrUrl = "http://localhost:8080/";

  private void OnLoaded(Object sender, RoutedEventArgs e)
  {
      try
      {
           WebRequest req = WebRequest.Create(new Uri(_svrUrl));
          req.Method = "GET";

          req.BeginGetResponse(new AsyncCallback(GetResponseCallback), req);
      }
      catch { }
  }

The callback method is called when the server return a response,
then I start reading data from the response stream asynchronously using ThreadPool class.

  private void GetResponseCallback(IAsyncResult ar)
  {
      try
      {
          WebRequest req = ar.AsyncState as WebRequest;
          WebResponse res = req.EndGetResponse(ar);

           Stream stream = res.GetResponseStream();

           ThreadPool.QueueUserWorkItem(new WaitCallback(ReadContents), stream);
      }
      catch { }
  }

In the last part,we deserialize the person class instance from the XML Stirng read from stream.

Be sure to use Dispather accessing to a control in a code block executed by a diffrent thread.

  private void ReadContents(Object stream)
  {
      Person person = null;

      using (StreamReader reader = new StreamReader(stream as Stream))
      {
          XmlSerializer serializer = new XmlSerializer(typeof(Person));

          person = serializer.Deserialize(reader) as Person;
      }

      Dispatcher.BeginInvoke(
          () => {
              _lastName.Text = person.LastName;
            _firstName.Text = person.FirstName;
          }
      );
  }