HttpWebRequest inside a custom class - windows-phone-7

Question

I'm trying to make an app for windows phone 7 mango, to parse the content of a website. I managed to write all the code, but it was like a war zone ;). When i tried to rearrange the code in a better way, i start facing a very strange problem.
The problem is when i made a custom class called "MedinetMySchedule" inside my project and use breakpoint to step through this class. I found out that the app steps throught the first method getrequest() then return back to the mainpage for few steps, then returns back to the second methods GetRequestStreamCallback(). This jump to the mainpage leaves me with a string having a value of null to parse. Then it jump back to the third method ReadWebRequestCallback(). This last jump gives me nothing important as the debugg ends and i get nothing on the phone-emulator. The MedinetMySchedule class has the following code:-
namespace WindowsPhonePanoramaApplication1
{
public class MedinetMySchedule
{
//Medinet user url
public string url { get; set; }
public String myresponse;
public void getrequest()
{
HttpWebRequest request = HttpWebRequest.CreateHttp(url);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.BeginGetRequestStream(GetRequestStreamCallback, request);
}
private void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
using (Stream postStream = request.EndGetRequestStream(asynchronousResult))
{
string postData = string.Format("username={0}&password={1}&customer=******&doLogin=Logga+in&language=se", "*****", "******");
// Convert the string into a byte array.
byte[] data = Encoding.UTF8.GetBytes(postData);
// Write to the request stream.
postStream.Write(data, 0, data.Length);
postStream.Close();
}
//Initiating get response
request.BeginGetResponse(ReadWebRequestCallBack, request);
}
private void ReadWebRequestCallBack(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
WebResponse myResponse = (WebResponse)request.EndGetResponse(asynchronousResult);
Stream encodingStream = myResponse.GetResponseStream();
Encoding encode = Encoding.GetEncoding("iso-8859-1");
using (StreamReader httpwebStreamReader = new StreamReader(encodingStream, encode))
{
myresponse= httpwebStreamReader.ReadToEnd();
}
myResponse.Close();
}
}
}
Here is the code that calls the getrequest() and parses the content:-
MedinetMySchedule mittschema = new MedinetMySchedule();
mittschema.url = "https://medinet.se/cgi-bin/doctor.pl?action=login&customer=saskir&language=se";
mittschema.getrequest();
Dispatcher.BeginInvoke(() => parseResults(mittschema.myresponse));
private void parseResults(string myresponse)
{
if (string.IsNullOrEmpty(myresponse))
{
return;
}
//Initiating a listbox and add item to it
List<MediNetScheme> medinetScheme = new List<MediNetScheme>();
//Using HtmlAgilityPack to parse the HTMLcode from the response
HtmlDocument htdoc = new HtmlDocument();
htdoc.LoadHtml(myresponse);
foreach (HtmlNode table in htdoc.DocumentNode.SelectNodes("//table[#class='list-medium']/tbody[1]/tr[#class]"))
{
//Removing ChildNode
table.ChildNodes.RemoveAt(3);
string itemValue = table.InnerText;
//Changing the parsed date into a DateTime
string d;
DateTime datum = DateTime.Parse(itemValue.Remove(11));
d = datum.ToString("D");
//Adding items to the listbox
medinetScheme.Add(new MediNetScheme() { Datum = d, Sections = itemValue.Remove(0, 15) });
}
MediNetScheme.ItemsSource = medinetScheme;
}
Any ideas why this is happening and how to correct it?
Yours
/Omar

Answer 1

The execution going back and forth is because request.BeginGetRequestStream is asynchronous. Basically, it creates a new thread, and executes in parallel of your main code. Therefore, you end up calling parseResult before you've finished downloading the data. There's many ways to rewrite your code, my favorite is using a callback:
First, change the getRequest method to accept a callback, and store it:
private Action Callback;
public void getrequest(Action callback)
{
this.Callback = callback;
HttpWebRequest request = HttpWebRequest.CreateHttp(url);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.BeginGetRequestStream(GetRequestStreamCallback, request);
}
Then, at the end of ReadWebRequestCallback, invoke this callback:
private void ReadWebRequestCallBack(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
WebResponse myResponse = (WebResponse)request.EndGetResponse(asynchronousResult);
Stream encodingStream = myResponse.GetResponseStream();
Encoding encode = Encoding.GetEncoding("iso-8859-1");
using (StreamReader httpwebStreamReader = new StreamReader(encodingStream, encode))
{
myresponse= httpwebStreamReader.ReadToEnd();
}
myResponse.Close();
this.Callback();
}
Finally, from mainpage, call the getrequest method and tell it to use parseResults as callback:
Action callback = () => Dispatcher.BeginInvoke(() => parseResults(mittschema.myresponse));
mittschema.getrequest(callback);