Question

I’m quite new at c# and am trying to build a program that logs into a website and returns it’s source code. Problem is, I register an event listener for when the page is loaded, but when I debug it it quits after setting the same event, not actually doing what I want it to do after the page “loads”.

Here’s the source –

using System;
using System.Windows.Forms;

namespace WIN
{
    class Program
    {
        string url = -snip-;
        string username = -snip-;
        string password = -snip-;
        string task = -snip-;
        string action = -snip-;
        string timezone = -snip-;

        private void Login()
        {
            Console.WriteLine("Started.");
            Console.ReadLine();
            Console.WriteLine("Declaring WebBrowser instance browser...");
            WebBrowser browser = new WebBrowser();
            Console.WriteLine("Done.");
            Console.ReadLine();
            Console.WriteLine("Registering an event for when the page finishes loading...");
            browser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(pageLoaded);
            Console.WriteLine("Done.");
            Console.ReadLine();
            Console.WriteLine("Using method Navigate of browser instance with url parameter...");
            browser.Navigate(url);
            Console.WriteLine("Done.");
            Console.ReadLine();

        }

        private void pageLoaded(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            Console.WriteLine("Declaring WebBrowser instance browser as sender...");
            WebBrowser browser = sender as WebBrowser;
            Console.WriteLine("Done.");
            Console.ReadLine();
            string response = browser.DocumentText;

            Console.WriteLine("Searching for authenticity token...");
            // looks in the page source to find the authenticity token.
            // could also use regular expressions here.
            int index = response.IndexOf("authenticity_token");
            int startIndex = index + 41;
            string authenticityToken = response.Substring(startIndex, 40);
            Console.WriteLine("Found authenticity token.");

            Console.WriteLine("Unregistering first event handler...");
            // unregisters the first event handler
            // adds a second event handler
            browser.DocumentCompleted -= new WebBrowserDocumentCompletedEventHandler(pageLoaded);
            Console.WriteLine("Done.");
            Console.WriteLine("Adding second event handler...");
            browser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(pageLoaded2);
            Console.WriteLine("Done.");
            Console.Read();

            Console.WriteLine("Formatting data to be posted to server...");
            string postData = string.Format("_user={0}&_pass={1}&authenticity_token={2}&_task{3}&_action{4}&_timezone{5}", username, password, authenticityToken, task, action, timezone);
            Console.WriteLine("Done.");
            Console.Read();

            Console.WriteLine("Declaring ASCIIEncoding instance enc...");
            System.Text.ASCIIEncoding enc = new System.Text.ASCIIEncoding();
            Console.WriteLine("Done.");
            Console.Read();

            //  we are encoding the postData to a byte array
            Console.WriteLine("Encoding postData to a byte array...");
            browser.Navigate(url, "", enc.GetBytes(postData), "Content-Type: application/x-www-form-urlencoded\r\n");
            Console.WriteLine("Done..");
            Console.Read();

        }

        [STAThread]
        static void Main(string[] args)
        {
            Program p = new Program();
            p.Login();
        }
    }
}

From all those console outputs, it only gets to Using method Navigate of browser instance with url parameter…

Answer 1

WebBrowser requires that your program pumps a message loop. It won’t fire its events otherwise. This is in general a requirement for any program that uses a single-threaded COM component. Or to put it in more understandable terms: you can’t get a program to be busy reading from the console and at the same time fire events like DocumentCompleted. A thread can do only one thing at time. You pump a message loop by writing a Winforms app or starting one yourself with Application.Run(). With a message loop, a thread can do more than one thing at a time. But that does require very different code from what you’ve written right now, you still can’t use Console.ReadLine(), you’d use a TextBox instead.

You can rescue what you have by running the browser in a separate thread, you’ll find the code you need for that in this answer.