WebBrowser Control in a new thread

I have a list Uri's that I want "clicked" To achieve this I"m trying to create a new web-browser control per Uri. I create a new thread per Uri. The problem I'm having is the thread end before the document is fully loaded, so I never get to make use of the DocumentComplete event. How can I overcome this?

var item = new ParameterizedThreadStart(ClicIt.Click); 
var thread = new Thread(item) {Name = "ClickThread"}; 
thread.Start(uriItem);

public static void Click(object o)
{
    var url = ((UriItem)o);
    Console.WriteLine(@"Clicking: " + url.Link);
    var clicker = new WebBrowser { ScriptErrorsSuppressed = true };
    clicker.DocumentCompleted += BrowseComplete;
    if (String.IsNullOrEmpty(url.Link)) return;
    if (url.Link.Equals("about:blank")) return;
    if (!url.Link.StartsWith("http://") && !url.Link.StartsWith("https://"))
        url.Link = "http://" + url.Link;
    clicker.Navigate(url.Link);
}

You have to create an STA thread that pumps a message loop. That's the only hospitable environment for an ActiveX component like WebBrowser. You won't get the DocumentCompleted event otherwise. Some sample code:

private void runBrowserThread(Uri url) {
    var th = new Thread(() => {
        var br = new WebBrowser();
        br.DocumentCompleted += browser_DocumentCompleted;
        br.Navigate(url);
        Application.Run();
    });
    th.SetApartmentState(ApartmentState.STA);
    th.Start();
}

void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) {
    var br = sender as WebBrowser;
    if (br.Url == e.Url) {
        Console.WriteLine("Natigated to {0}", e.Url);
        Application.ExitThread();   // Stops the thread
    }
}

Here is how to organize a message loop on a non-UI thread, to run asynchronous tasks like WebBrowser automation. It uses async/await to provide the convenient linear code flow and loads a set of web pages in a loop. The code is a ready-to-run console app which is partially based on this excellent post.

Related answers:

• https://stackoverflow.com/a/22262976/1768303

• https://stackoverflow.com/a/21775343/1768303

  using System; using System.Threading; using System.Threading.Tasks; using System.Windows.Forms;

  namespace ConsoleApplicationWebBrowser { // by Noseratio - https://stackoverflow.com/users/1768303/noseratio class Program { // Entry Point of the console app static void Main(string[] args) { try { // download each page and dump the content var task = MessageLoopWorker.Run(DoWorkAsync, "http://www.example.com";, "http://www.example.net";, "http://www.example.org";); task.Wait(); Console.WriteLine("DoWorkAsync completed."); } catch (Exception ex) { Console.WriteLine("DoWorkAsync failed: " + ex.Message); }

           Console.WriteLine("Press Enter to exit.");
           Console.ReadLine();
       }
  
       // navigate WebBrowser to the list of urls in a loop
       static async Task<object> DoWorkAsync(object[] args)
       {
           Console.WriteLine("Start working.");
  
           using (var wb = new WebBrowser())
           {
               wb.ScriptErrorsSuppressed = true;
  
               TaskCompletionSource<bool> tcs = null;
               WebBrowserDocumentCompletedEventHandler documentCompletedHandler = (s, e) =>
                   tcs.TrySetResult(true);
  
               // navigate to each URL in the list
               foreach (var url in args)
               {
                   tcs = new TaskCompletionSource<bool>();
                   wb.DocumentCompleted += documentCompletedHandler;
                   try
                   {
                       wb.Navigate(url.ToString());
                       // await for DocumentCompleted
                       await tcs.Task;
                   }
                   finally
                   {
                       wb.DocumentCompleted -= documentCompletedHandler;
                   }
                   // the DOM is ready
                   Console.WriteLine(url.ToString());
                   Console.WriteLine(wb.Document.Body.OuterHtml);
               }
           }
  
           Console.WriteLine("End working.");
           return null;
       }
  
   }
  
   // a helper class to start the message loop and execute an asynchronous task
   public static class MessageLoopWorker
   {
       public static async Task<object> Run(Func<object[], Task<object>> worker, params object[] args)
       {
           var tcs = new TaskCompletionSource<object>();
  
           var thread = new Thread(() =>
           {
               EventHandler idleHandler = null;
  
               idleHandler = async (s, e) =>
               {
                   // handle Application.Idle just once
                   Application.Idle -= idleHandler;
  
                   // return to the message loop
                   await Task.Yield();
  
                   // and continue asynchronously
                   // propogate the result or exception
                   try
                   {
                       var result = await worker(args);
                       tcs.SetResult(result);
                   }
                   catch (Exception ex)
                   {
                       tcs.SetException(ex);
                   }
  
                   // signal to exit the message loop
                   // Application.Run will exit at this point
                   Application.ExitThread();
               };
  
               // handle Application.Idle just once
               // to make sure we're inside the message loop
               // and SynchronizationContext has been correctly installed
               Application.Idle += idleHandler;
               Application.Run();
           });
  
           // set STA model for the new thread
           thread.SetApartmentState(ApartmentState.STA);
  
           // start the thread and await for the task
           thread.Start();
           try
           {
               return await tcs.Task;
           }
           finally
           {
               thread.Join();
           }
       }
   }
  

  }

From my experience in the past the webbrowser does not like operating outside of the main application thread.

Try using httpwebrequests instead, you can set them as asynchronous and create a handler for the response to know when it is succesfull:

how-to-use-httpwebrequest-net-asynchronously

A simple solution at which the simultaneous operation of several WebBrowsers occurs

1. Create a new Windows Forms application

2. Place the button named button1

3. Place the text box named textBox1

4. Set properties of text field: Multiline true and ScrollBars Both

5. Write the following button1 click handler:

   textBox1.Clear();
   textBox1.AppendText(DateTime.Now.ToString() + Environment.NewLine);
   int completed_count = 0;
   int count = 10;
   for (int i = 0; i < count; i++)
   {
       int tmp = i;
       this.BeginInvoke(new Action(() =>
       {
           var wb = new WebBrowser();
           wb.ScriptErrorsSuppressed = true;
           wb.DocumentCompleted += (cur_sender, cur_e) =>
           {
               var cur_wb = cur_sender as WebBrowser;
               if (cur_wb.Url == cur_e.Url)
               {
                   textBox1.AppendText("Task " + tmp + ", navigated to " + cur_e.Url + Environment.NewLine);
                   completed_count++;
               }
           };
           wb.Navigate("https://stackoverflow.com/questions/4269800/webbrowser-control-in-a-new-thread");
       }
       ));
   }
   
   while (completed_count != count)
   {
       Application.DoEvents();
       Thread.Sleep(10);
   }
   textBox1.AppendText("All completed" + Environment.NewLine);