WebBrowser control external scripting doesn't work

This is the HTML, which is stored in a string resource:

<!DOCTYPE html>
<html>
    <head></head>
    <body>
        <script>
           (function(){
               window.external.hello()
           })()
        </script>
    </body> 
</html>

This is the contents of Form1.cs:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace JSIE
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            webBrowser1.Navigate("about:blank");
            webBrowser1.Document.Write(String.Empty);
            webBrowser1.Document.Write(Properties.Resources.DDocument);
            webBrowser1.ObjectForScripting = new JSCallbacks();
        }
    }
}

and this is JSCallbacks.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Permissions;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace JSIE
{
    [PermissionSet(SecurityAction.Demand, Name = "FullTrust")]
    [ComVisible(true)]

    public class JSCallbacks
    {
        public void hello() {
            MessageBox.Show("Hello, world!");
        }
    }
}

When I run this, it can't access the hello() method in the JavaScript window.external object, and gives me a script error message box. I have tried using this as the ObjectForScripting, but it doesn't work either.

Solution

Got it: You have to use the DocumentText property to load HTML before the page is executed.