How to Reliably Handle WebBrowser Control Navigation Completion in a Separate Thread?

Web Browser Automation: Ensuring Navigation Completion on a Separate Thread

Automating web browsing with a WebBrowser control in a separate thread often presents challenges with detecting document load completion. The DocumentCompleted event might not fire before the thread ends, preventing access to the loaded document.

The Solution: Utilizing an STA Thread

The key to resolving this is using a Single-Threaded Apartment (STA) thread and a message loop. STA threads provide the necessary environment for ActiveX components like WebBrowser. Here's how to implement this:

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

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

This StartBrowserThread method creates an STA thread. Application.Run() initiates a message pump, crucial for the WebBrowser control's event handling. The WebBrowser_DocumentCompleted event handler confirms navigation completion, logs the URL, and then terminates the thread using Application.ExitThread(), ensuring clean resource management.

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