Comments

1. Ahmed Behairy
   08 Jan 2010 at 09:26

   Steve thanks for the article. It was really helpful. I am working on a project that somehow uses the web request technique. But I'm facing a tough problem, my application is a web scrapping application. The website I'm scrapping has a combo box list and which of course fires a do post back on change. I want to use the web request to raise or fire the event of the do post back with the value I want and extract the web source page. is that possible?

   Thanks in Advance, Happy holidays Beheiry

2. Adeyemi Opanuga
   16 Aug 2009 at 12:21

   Thanks for this article but I have a question concerning making asynchronous http requests. Is it possible to call the same script say [ http://buzzme.com/index.aspx?message=tasty ] three thousand times (3,000) asynchronously to submit different message parameters without it breaking? ... and at the same time getting the response of each request and logging the output somewhere in a db.

3. Adeyemi Opanuga
   16 Aug 2009 at 09:11

   Thanks for this article but I have a question concerning making asynchronous http requests. Is it possible to call the same script say [ http://buzzme.com/index.aspx?message=tasty ] three thousand times (3,000) asynchronously to submit different message parameters without it breaking? ... and at the same time getting the response of each request and logging the output somewhere in a db.

4. trey paschal
   18 Feb 2009 at 18:37
   It took me about 4 hrs searching around the inter webz to finally wrap my head around this concept. After digging through incomplete and just plain wrong code I ended up putting together a complete working example, from informayion found in a few different posts. The code below is not commented as the original poster in this forum did a great job of explaing, too bad he left some classes and, how to handle the cross threaded response. Enjoy Hope this makes some ones learning experience easier than mine was. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Threading; using System.Net; using System.IO; namespace sampleApp { public partial class Form1 : Form { List list = new List(); public DelegateAddString t_DelegateAddString; public Form1() { InitializeComponent(); t_DelegateAddString = new DelegateAddString(this.TbAddString); } private void Form1_Load(object sender, EventArgs e) { list.Add("http://google.com"); list.Add("http://yahoo.com"); list.Add("http://msn.com"); list.Add("http://aol.com"); } private void TbAddString(String str) { textBox1.Text += (str); } private void button1_Click(object sender, EventArgs e) { Thread t = new Thread(ScanSites); t.IsBackground = true; t.Start(); } private void ScanSites() { foreach (string uri in list) { WebRequest request = HttpWebRequest.Create(uri); request.Method = "GET"; object data = new object(); RequestState state = new RequestState(request, data, uri); IAsyncResult result = request.BeginGetResponse( new AsyncCallback(UpdateItem), state); ThreadPool.RegisterWaitForSingleObject( result.AsyncWaitHandle, new WaitOrTimerCallback(ScanTimeoutCallback), state, (30 * 1000), true); } } private void UpdateItem(IAsyncResult result) { String str; RequestState state = (RequestState)result.AsyncState; WebRequest request = (WebRequest)state.Request; HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result); Stream s=(Stream)response.GetResponseStream(); StreamReader readStream = new StreamReader( s ); string dataString= readStream.ReadToEnd(); response.Close(); s.Close(); readStream.Close(); string lastMod = String.Empty; if (response.Headers["last-modified"] != null) lastMod = response.Headers["last-modified"]; str = "Read: " + state.SiteUrl + ": " + response.ContentLength.ToString() + " bytes. Last-Mod: " + lastMod; Thread.Sleep(400); Invoke(t_DelegateAddString, new Object[] { str }); } private static void ScanTimeoutCallback(object state, bool timedOut) { if (timedOut) { RequestState reqState = (RequestState)state; if (reqState != null) reqState.Request.Abort(); MessageBox.Show("aborted- timeout"); } } class RequestState { public WebRequest Request; // holds the request public object Data; // store any data in this public string SiteUrl; // holds the UrlString to match up results (Database lookup, etc). public RequestState(WebRequest request, object data, string siteUrl) { this.Request = request; this.Data = data; this.SiteUrl = siteUrl; } } } }
5. gabe garza
   22 May 2007 at 20:17

   "Careful with that Axe Eugene" - I love that song.

    

6. Bernd Truckses
   30 Mar 2006 at 18:45

   Hi Steven
   
   I've got the following problem and your proposal seems to be the solution:
   
   

   I want to do a asynchronous Request, where I have to post a large amount of data to some old asp - component. "Asynchronous" means for me to start the posting and imideately continue with my workflow while in background the huge amount of data is posting...

   therrefore I call as suggested in msdn - help:

   // Start the asynchronous request.
   
   IAsyncResult result = ( IAsyncResult ) httpRequest.BeginGetResponse ( new AsyncCallback ( RespCallback ), state );

   // this line implements the timeout, if there is a timeout, the callback fires and the request becomes aborted
   
   ThreadPool.RegisterWaitForSingleObject (
   result.AsyncWaitHandle, new WaitOrTimerCallback ( TimeoutCallback ),
   httpRequest, DefaultTimeout, true );
   
   Now I set my breakpoint in the RespCallback() - Method and here'se the problem:
   after BeginGetResponse () the process first jumps to RespCallback() and then jumps to RegisterWaitForSingleObject()
   
   So this is not realy asynchronous...
   Did I miss something or is this general behaviour ?
   
   after trying your solution (perform this request in an extra thread) I saw that this would be the right way but I have some questions left:
   
   If you start this request in an extra thread, why do you make this request asynchronous ?
   I think, asynchronity in this place is achieved by the extra thread which runs in the background
   
   Is there a way to achieve the asynchronity I want without this extra thread (I'm not sure that what I want realy matches the meaning of "asynchronity" used by BeginGetResponse() ... EndGetResponse() ) ?
   
   
   thanx in advance and nice greetings
     Bernd
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

7. Developer Fusion Bot
   01 Jan 1999 at 00:00

   This thread is for discussions of Asynchronous HttpWebRequest.