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Revision: 6185
at May 5, 2008 17:21 by BlueCockatoo
Initial Code 
byte[] response;

WebClient webClient = new WebClient();
response = webClient.DownloadData(LOGIN_URL);

string viewstate = ExtractViewState(
      Encoding.ASCII.GetString(response)
   );

string postData = String.Format(
   "__VIEWSTATE={0}&UsernameTextBox={1}&PasswordTextBox={2}&LoginButton=Login",
   viewstate, USERNAME, PASSWORD);

webClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
response = webClient.UploadData(
        LOGIN_URL, "POST", Encoding.ASCII.GetBytes(postData)
    );

private string ExtractViewState(string s)
{
   string viewStateNameDelimiter = "__VIEWSTATE";
   string valueDelimiter = "value=\"";
            
   int viewStateNamePosition = s.IndexOf(viewStateNameDelimiter);     
   int viewStateValuePosition = s.IndexOf(
         valueDelimiter, viewStateNamePosition
      );

   int viewStateStartPosition = viewStateValuePosition + 
                                valueDelimiter.Length;
   int viewStateEndPosition = s.IndexOf("\"", viewStateStartPosition);

   return HttpUtility.UrlEncodeUnicode(
            s.Substring(
               viewStateStartPosition, 
               viewStateEndPosition - viewStateStartPosition
            )
         );  
}
Initial URL 
http://odetocode.com/articles/162.aspx
Initial Description 
How to use WebClient to post to an ASP.Net page and maintain viewstate for proxy purposes.
Initial Title 
Screen Scraping, ViewState, and Authentication using ASP.Net
Initial Tags 
c, aspnet
Initial Language 
C#