The method of modifying the User-Agent of the WebBrowser control in Winform (the test has been successful)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Reflection;
namespace WindowsFormsApplication2
{
public class UserAgentHelper
{
    private static string defaultUserAgent = null;
    [DllImport("urlmon.dll", CharSet = CharSet.Ansi)]
    private static extern int UrlMkSetSessionOption(int dwOption, string pBuffer, int dwBufferLength, int dwReserved);
    const int URLMON_OPTION_USERAGENT = 0x10000001;
    /// <summary>
    /// Add a part after the default UserAgent
    /// </summary>
    public static void AppendUserAgent(string appendUserAgent)
    {
      if (string.IsNullOrEmpty(defaultUserAgent))
        defaultUserAgent = GetDefaultUserAgent();
      string ua = defaultUserAgent   ";"   appendUserAgent;
      ChangeUserAgent(ua);
    }
    /// <summary>
    /// Modify UserAgent
    /// </summary>
    public static void ChangeUserAgent(string userAgent)
    {
      UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, userAgent, userAgent.Length, 0);
    }
    /// <summary>
    /// A very BT method to get the default UserAgent of IE
    /// </summary>
    private static string GetDefaultUserAgent()
    {
      WebBrowser wb = new WebBrowser ();
      wb.Navigate("about:blank");
      while (wb.IsBusy) Application.DoEvents();
      object window = wb.Document.Window.DomWindow;
      Type wt = window.GetType();
      object navigator = wt.InvokeMember("navigator", BindingFlags.GetProperty,
          null, window, new object[] { });
      Type nt = navigator.GetType();
      object userAgent = nt.InvokeMember("userAgent", BindingFlags.GetProperty,
          null, navigator, new object[] { });
      return userAgent.ToString();
    }
}
}