c# - Get ReadyState from WebBrowser control without DoEvents

Question

This has been awnsered many times here and at other sites and its working, but I would like ideas to other ways to:

get the ReadyState = Complete after using a navigate or post, without using DoEvents because of all of its cons.

I would also note that using the DocumentComplete event woud not help here as I wont be navigating on only one page, but one after another like this.

wb.navigate("www.microsoft.com")
//dont use DoEvents loop here
wb.Document.Body.SetAttribute(textbox1, "login")
//dont use DoEvents loop here
if (wb.documenttext.contais("text"))
//do something

The way it is today its working by using DoEvents. I would like to know if anyone have a proper way to wait the async call of the browser methods to only then proceed with the rest of the logic. Just for the sake of it.

Thanks in advance.

Answer 1

Below is a basic WinForms app code, illustrating how to wait for the DocumentCompleted event asynchronously, using async/await. It navigates to multiple pages, one after another. Everything is taking place on the main UI thread.

Instead of calling this.webBrowser.Navigate(url), it might be simulating a form button click, to trigger a POST-style navigation.

The webBrowser.IsBusy async loop logic is optional, its purpose is to account (non-deterministically) for the page's dynamic AJAX code which may take place after window.onload event.

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

namespace WebBrowserApp
{
    public partial class MainForm : Form
    {
        WebBrowser webBrowser;

        public MainForm()
        {
            InitializeComponent();

            // create a WebBrowser
            this.webBrowser = new WebBrowser();
            this.webBrowser.Dock = DockStyle.Fill;
            this.Controls.Add(this.webBrowser);

            this.Load += MainForm_Load;
        }

        // Form Load event handler
        async void MainForm_Load(object sender, EventArgs e)
        {
            // cancel the whole operation in 30 sec
            var cts = new CancellationTokenSource(30000);

            var urls = new String[] { 
                    "http://www.example.com", 
                    "http://www.gnu.org", 
                    "http://www.debian.org" };

            await NavigateInLoopAsync(urls, cts.Token);
        }

        // navigate to each URL in a loop
        async Task NavigateInLoopAsync(string[] urls, CancellationToken ct)
        {
            foreach (var url in urls)
            {
                ct.ThrowIfCancellationRequested();
                var html = await NavigateAsync(ct, () => 
                    this.webBrowser.Navigate(url));
                Debug.Print("url: {0}, html: 
{1}", url, html);
            }
        }

        // asynchronous navigation
        async Task<string> NavigateAsync(CancellationToken ct, Action startNavigation)
        {
            var onloadTcs = new TaskCompletionSource<bool>();
            EventHandler onloadEventHandler = null;

            WebBrowserDocumentCompletedEventHandler documentCompletedHandler = delegate
            {
                // DocumentCompleted may be called several time for the same page,
                // if the page has frames
                if (onloadEventHandler != null)
                    return;

                // so, observe DOM onload event to make sure the document is fully loaded
                onloadEventHandler = (s, e) =>
                    onloadTcs.TrySetResult(true);
                this.webBrowser.Document.Window.AttachEventHandler("onload", onloadEventHandler);
            };

            this.webBrowser.DocumentCompleted += documentCompletedHandler;
            try
            {
                using (ct.Register(() => onloadTcs.TrySetCanceled(), useSynchronizationContext: true))
                {
                    startNavigation();
                    // wait for DOM onload event, throw if cancelled
                    await onloadTcs.Task;
                }
            }
            finally
            {
                this.webBrowser.DocumentCompleted -= documentCompletedHandler;
                if (onloadEventHandler != null)
                    this.webBrowser.Document.Window.DetachEventHandler("onload", onloadEventHandler);
            }

            // the page has fully loaded by now

            // optional: let the page run its dynamic AJAX code,
            // we might add another timeout for this loop
            do { await Task.Delay(500, ct); }
            while (this.webBrowser.IsBusy);

            // return the page's HTML content
            return this.webBrowser.Document.GetElementsByTagName("html")[0].OuterHtml;
        }
    }
}

If you're looking to do something similar from a console app, here is an example of that.