public class WebBrowserEventManager
{
    private EventHandlerList _ehList = new EventHandlerList();
    private WebBrowser _wb = null;

    /// <summary>
    /// 构造函数
    /// </summary>
    /// <param name="webbrowser"></param>
    public WebBrowserEventManager(WebBrowser webbrowser)
    {
        _wb = webbrowser;
    }

    /// <summary>
    /// 注册事件(不可重复注册)
    /// </summary>
    /// <param name="eventHandler"></param>
    public void AddDocumentCompletedEvent(WebBrowserDocumentCompletedEventHandler eventHandler)
    {
        RemoveDocumentCompletedEvent(eventHandler);
        _wb.DocumentCompleted += eventHandler;
        _ehList.AddHandler(_wb.Name, eventHandler);
    }

    /// <summary>
    /// 注册事件(移除全部事件再注册)
    /// </summary>
    /// <param name="eventHandler"></param>
    public void AddDocumentCompletedEventEx(WebBrowserDocumentCompletedEventHandler eventHandler)
    {
        RemoveAllDocumentCompletedEvent();
        _wb.DocumentCompleted += eventHandler;
        _ehList.AddHandler(_wb.Name, eventHandler);
    }

    /// <summary>
    /// 移除事件
    /// </summary>
    /// <param name="eventHandler"></param>
    public void RemoveDocumentCompletedEvent(WebBrowserDocumentCompletedEventHandler eventHandler)
    {
        Delegate dg = _ehList[_wb.Name];
        if (dg != null)
        {
            Delegate[] ivList = dg.GetInvocationList();
            if (ivList != null)
            {
                for (int i = ivList.Length - 1; i >= 0; i--)
                {
                    if (eventHandler == null || (eventHandler != null && (ivList[i] as WebBrowserDocumentCompletedEventHandler) == eventHandler))
                    {
                        _wb.DocumentCompleted -= ivList[i] as WebBrowserDocumentCompletedEventHandler;
                        _ehList.RemoveHandler(_wb.Name, ivList[i]);
                    }
                    //return; //不退出循环移除重复注册事件
                }
            }
        }
    }

    /// <summary>
    /// 移除全部事件
    /// </summary>
    public void RemoveAllDocumentCompletedEvent()
    {
        RemoveDocumentCompletedEvent(null);
    }
}

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private WebBrowserEventManager manager;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            manager = new WebBrowserEventManager(webBrowser1);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            manager.AddDocumentCompletedEventEx(Todo1);
            webBrowser1.Navigate("http://www.baidu.com/");
        }

        private void button2_Click(object sender, EventArgs e)
        {
            manager.AddDocumentCompletedEventEx(Todo2);
            webBrowser1.Navigate("http://www.google.com/");
        }

        private void Todo1(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            MessageBox.Show("打开了百度。");
            //针对百度页面的操作
        }

        private void Todo2(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            MessageBox.Show("打开了谷歌。");
            //针对谷歌页面的操作
        }
    }
}