C# WebClient, Post and Submit

Posted on 2011-10-16
Medium Priority
Last Modified: 2012-06-27
I'm learning about WebClient by using it to collect some data from a web page.  I've attached the page source as I see it through FireFox.

I want to post a zip code to the page, and then press the search button.

I think (but not sure) I'm posting the data correctly.  I don't see how to press the search button.

Here is my current code:
using System;
using System.Collections.Specialized;
using System.IO;
using System.Net;
using System.Text;

class Demo {
   static void Main(string[] args) {
      NameValueCollection nvc = new NameValueCollection();
      String response = TestPost("http://www.leginfo.ca.gov/yourleg.html",nvc);

   static String TestPost(String url,NameValueCollection nvc) {
      WebClient webClient = new WebClient();
      byte[] response = webClient.UploadValues(url,"POST",nvc);
      return System.Text.Encoding.UTF8.GetString(response);

Question by:josgood
  • 2
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LVL 75

Accepted Solution

käµfm³d   👽 earned 2000 total points
ID: 36976247
You have to understand how the web works. Buttons, text boxes, drop-down lists...  those are conveniences for users. You computer (and the remote computer) only care about data coming across the wire. To post to a page programmatically, you would not "click" the submit button; rather you would craft a message similar to that which your browser sends when you click the submit button.

For example, if you look at the source code for the page, the submit button is contained within a <form> tag. This <form> tag has an action. For web forms, the action attribute specifies to which page you are going to send data. In this case, the data will go to the default page located at "/cgi-bin/memberinfo" (either that, or that URL is rewritten on the server to some other URL, but you wouldn't know this unless you maintained that server). What you need to do is mimic this behavior.

How does one do that? Well, you've got a good chunk of the code set up already. You will be passing values back to the site, and you will be using the POST method, but you need to change the URL that you are pointing to. If I am not mistaken, it should be:

String response = TestPost("http://www.leginfo.ca.gov/cgi-bin/memberinfo",nvc);

Open in new window

This is because the URL in the action attribute is rooted (starts with a forward slash), so it should be found at root directory of the site. I haven't tested the code, but I believe that is all you should need to change.
LVL 13

Author Comment

ID: 36976283
Fabulous!  Exactly what I was looking for!

Your explanation is very clear and I appreciate it.  I did not understand the action attribute.  Now I know a bit more and I will read up on it.

Thank you very much for your help.

LVL 13

Author Comment

ID: 36976288
BTW, your fix works!
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 36978842
NP. Glad to help  = )

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