How Can I Reliably Use the WebBrowser Control's DocumentComplete Event in a New Thread?

Addressing WebBrowser Control Challenges in Multithreaded Environments

Web scraping and automation often involve multithreading for efficient web request processing. However, using the WebBrowser control within a separate thread presents significant difficulties, especially concerning the DocumentComplete event, crucial for ensuring complete page load before data extraction or interaction.

The Core Problem:

The WebBrowser control, being an ActiveX component, necessitates an STA (Single-Threaded Apartment) thread with a message pump. Standard .NET threads are typically MTA (Multi-Threaded Apartment) threads, lacking this essential requirement.

The Solution: Explicit STA Thread Creation

The solution involves creating an STA thread and explicitly starting a message pump within it. Here's an illustrative example:

<code class="language-csharp">private void RunBrowserThread(Uri url)
{
    var thread = new Thread(() =>
    {
        var webBrowser = new WebBrowser();
        webBrowser.DocumentCompleted += Browser_DocumentCompleted;
        webBrowser.Navigate(url);
        Application.Run(); // Crucial for the message pump
    });
    thread.SetApartmentState(ApartmentState.STA);
    thread.Start();
}

private void Browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    var webBrowser = (WebBrowser)sender;
    if (webBrowser.Url == e.Url)
    {
        Console.WriteLine($"Navigated to {e.Url}");
        Application.ExitThread(); // Safely terminates the thread
    }
}</code>

This code creates a new STA thread, assigns the WebBrowser to it, subscribes to the DocumentCompleted event, and importantly, includes Application.Run() to initiate the message pump. Upon event firing, Application.ExitThread() cleanly stops the thread. This ensures reliable DocumentComplete event triggering.

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