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>

    /// 在默认的UserAgent后面加一部分

    /// </summary>

    public static void AppendUserAgent(string appendUserAgent)

    {

      if (string.IsNullOrEmpty(defaultUserAgent))

        defaultUserAgent = GetDefaultUserAgent();

      string ua = defaultUserAgent   ";"   appendUserAgent;

      ChangeUserAgent(ua);

    }

    /// <summary>

    /// 修改UserAgent

    /// </summary>

    public static void ChangeUserAgent(string userAgent)

    {

      UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, userAgent, userAgent.Length, );

    }

    /// <summary>

    /// 一个很BT的获取IE默认UserAgent的方法

    /// </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();

    }

}

}