■

パーツその１：WebBrowserEx.cs
（パーツ２も作ってください）

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

namespace ABCS.Classes
{
    public class WebBrowserEx : ExtendedWebBrowser
    {
        #region NewWindow2 イベント関連

        private AxHost.ConnectionPointCookie cookie;
        private WebBrowser2EventHelper helper;

        [DesignerSerializationVisibility(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
        [DispIdAttribute(200)]
        public object Application
        {
            get
            {
                if (this.ActiveXInstance == null)
                {
                    throw new AxHost.InvalidActiveXStateException("Application", AxHost.ActiveXInvokeKind.PropertyGet);
                }
                return (this.ActiveXInstance as IWebBrowser2).Application;
            }
        }

        [DesignerSerializationVisibility(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
        [DispIdAttribute(552)]
        public bool RegisterAsBrowser
        {
            get
            {
                if (this.ActiveXInstance == null)
                {
                    throw new AxHost.InvalidActiveXStateException("RegisterAsBrowser", AxHost.ActiveXInvokeKind.PropertyGet);
                }
                return (this.ActiveXInstance as IWebBrowser2).RegisterAsBrowser;
            }
            set
            {
                if (this.ActiveXInstance == null)
                {
                    throw new AxHost.InvalidActiveXStateException("RegisterAsBrowser", AxHost.ActiveXInvokeKind.PropertyGet);
                }
                (this.ActiveXInstance as IWebBrowser2).RegisterAsBrowser = value;
            }
        }

        [PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
        protected override void CreateSink()
        {
            base.CreateSink();
            helper = new WebBrowser2EventHelper(this);
            cookie = new AxHost.ConnectionPointCookie(this.ActiveXInstance, helper, typeof(DWebBrowserEvents2));
        }

        [PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
        protected override void DetachSink()
        {
            if (cookie != null)
            {
                cookie.Disconnect();
                cookie = null;
            }
            base.DetachSink();
        }

        public event WebBrowserNewWindow2EventHandler NewWindow2;

        protected virtual void OnNewWindow2(WebBrowserNewWindow2EventArgs e)
        {
            NewWindow2(this, e);
        }

        private class WebBrowser2EventHelper : StandardOleMarshalObject, DWebBrowserEvents2
        {
            private WebBrowserEx parent;

            public WebBrowser2EventHelper(WebBrowserEx parent)
            {
                this.parent = parent;
            }

            public void NewWindow2(ref object ppDisp, ref bool cancel)
            {
                WebBrowserNewWindow2EventArgs e = new WebBrowserNewWindow2EventArgs(ppDisp);
                this.parent.OnNewWindow2(e);
                ppDisp = e.ppDisp;
                cancel = e.Cancel;
            }


            void ABCS.Classes.ExtendedWebBrowser.DWebBrowserEvents2.NewWindow3(object ppDisp, ref bool cancel, ref object a2, ref object a3, ref object a4)
            {
                WebBrowserNewWindow2EventArgs e = new WebBrowserNewWindow2EventArgs(ppDisp);
                this.parent.OnNewWindow2(e);
                ppDisp = e.ppDisp;
                cancel = e.Cancel;
            }

            void ABCS.Classes.ExtendedWebBrowser.DWebBrowserEvents2.BeforeNavigate2(object sender, ref object a1, ref object a2, ref object a3, ref object a4, ref object a5, ref bool a6)
            {
            }


        }
        #endregion

    }

    public delegate void WebBrowserNewWindow2EventHandler(object sender, WebBrowserNewWindow2EventArgs e);

    public class WebBrowserNewWindow2EventArgs : CancelEventArgs
    {
        private object ppdisp_ = null;
        public object ppDisp
        {
            get
            {
                return this.ppdisp_;
            }
            set
            {
                this.ppdisp_ = value;
            }
        }

        public WebBrowserNewWindow2EventArgs(object ppDisp)
        {
            this.ppDisp = ppDisp;
        }
    }

    [ComImport, Guid("34A715A0-6587-11D0-924A-0020AFC7AC4D")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    [TypeLibType(TypeLibTypeFlags.FHidden)]
    public interface DWebBrowserEvents2
    {
        [DispId(251)]
        void NewWindow2(
        [InAttribute(), OutAttribute(), MarshalAs(UnmanagedType.IDispatch)] ref object ppDisp,
        [InAttribute(), OutAttribute()] ref bool cancel);
    }

    [ComImport, Guid("D30C1661-CDAF-11D0-8A3E-00C04FC9E26E")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface IWebBrowser2
    {
        object Application { get; }
        bool RegisterAsBrowser { get; set; }
    }




    public class WebBrowserExtendedNavigatingEventArgs : CancelEventArgs
    {
        private string _Url;
        public string Url
        {
            get { return _Url; }
        }

        private string _Frame;
        public string Frame
        {
            get { return _Frame; }
        }

        public WebBrowserExtendedNavigatingEventArgs(string url, string frame)
            : base()
        {
            _Url = url;
            _Frame = frame;
        }
    }

    public class ExtendedWebBrowser : System.Windows.Forms.WebBrowser
    {
        protected string url_ = null;

        System.Windows.Forms.AxHost.ConnectionPointCookie cookie;
        WebBrowserExtendedEvents events;

        //This method will be called to give you a chance to create your own event sink
        protected override void CreateSink()
        {
            //MAKE SURE TO CALL THE BASE or the normal events won't fire
            base.CreateSink();
            events = new WebBrowserExtendedEvents(this);
            cookie = new System.Windows.Forms.AxHost.ConnectionPointCookie(this.ActiveXInstance, events, typeof(DWebBrowserEvents2));
        }

        protected override void DetachSink()
        {
            if (null != cookie)
            {
                cookie.Disconnect();
                cookie = null;
            }
            base.DetachSink();
        }

        //This new event will fire when the page is navigating
        public event EventHandler BeforeNavigate;
        public event EventHandler BeforeNewWindow;

        protected void OnBeforeNewWindow(string url, out bool cancel)
        {
            EventHandler h = BeforeNewWindow;
            WebBrowserExtendedNavigatingEventArgs args = new WebBrowserExtendedNavigatingEventArgs(url, null);
            if (null != h)
            {
                h(this, args);
            }
            cancel = args.Cancel;
        }

        protected void OnBeforeNavigate(string url, string frame, out bool cancel)
        {
            EventHandler h = BeforeNavigate;
            WebBrowserExtendedNavigatingEventArgs args = new WebBrowserExtendedNavigatingEventArgs(url, frame);
            if (null != h)
            {
                h(this, args);
            }
            //Pass the cancellation chosen back out to the events
            cancel = args.Cancel;
        }

        //This class will capture events from the WebBrowser
        class WebBrowserExtendedEvents : System.Runtime.InteropServices.StandardOleMarshalObject, DWebBrowserEvents2
        {
            ExtendedWebBrowser _Browser;
            public WebBrowserExtendedEvents(ExtendedWebBrowser browser) { _Browser = browser; }

            //Implement whichever events you wish
            public void BeforeNavigate2(object pDisp, ref object URL, ref object flags, ref object targetFrameName, ref object postData, ref object headers, ref bool cancel)
            {
                _Browser.OnBeforeNavigate((string)URL, (string)targetFrameName, out cancel);
                _Browser.url_ = URL.ToString();
            }

            public void NewWindow3(object pDisp, ref bool cancel, ref object flags, ref object URLContext, ref object URL)
            {
                _Browser.OnBeforeNewWindow((string)URL, out cancel);
            }

        }

        [System.Runtime.InteropServices.ComImport(), System.Runtime.InteropServices.Guid("34A715A0-6587-11D0-924A-0020AFC7AC4D"),
        System.Runtime.InteropServices.InterfaceTypeAttribute(System.Runtime.InteropServices.ComInterfaceType.InterfaceIsIDispatch),
        System.Runtime.InteropServices.TypeLibType(System.Runtime.InteropServices.TypeLibTypeFlags.FHidden)]
        public interface DWebBrowserEvents2
        {

            [System.Runtime.InteropServices.DispId(250)]
            void BeforeNavigate2(
                [System.Runtime.InteropServices.In,
                System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.IDispatch)] object pDisp,
                [System.Runtime.InteropServices.In] ref object URL,
                [System.Runtime.InteropServices.In] ref object flags,
                [System.Runtime.InteropServices.In] ref object targetFrameName, [System.Runtime.InteropServices.In] ref object postData,
                [System.Runtime.InteropServices.In] ref object headers,
                [System.Runtime.InteropServices.In,
                System.Runtime.InteropServices.Out] ref bool cancel);
            [System.Runtime.InteropServices.DispId(273)]
            void NewWindow3(
                [System.Runtime.InteropServices.In,
                System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.IDispatch)] object pDisp,
                [System.Runtime.InteropServices.In, System.Runtime.InteropServices.Out] ref bool cancel,
                [System.Runtime.InteropServices.In] ref object flags,
                [System.Runtime.InteropServices.In] ref object URLContext,
                [System.Runtime.InteropServices.In] ref object URL);
        }
    }

}

パーツその２：MyWebBrowser.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace ABCS.Classes
{
    public class MyWebBrowser : WebBrowserEx
    {
        private string beforeurl_ = null;

        public MyWebBrowser()
            : base()
        {
            this.NewWindow2 += new WebBrowserNewWindow2EventHandler(myWebBrowser_NewWindow2);
            this.BeforeNewWindow += new EventHandler(OnMyBeforeNewWindow);

        }

        protected void OnMyBeforeNewWindow(object sender, EventArgs e)
        {
            WebBrowserExtendedNavigatingEventArgs we = e as WebBrowserExtendedNavigatingEventArgs;
            if (we != null)
            {
                this.beforeurl_ = we.Url;
            }
        }
        // 新しくウィンドウを開かれようとするときに発生する
        void myWebBrowser_NewWindow2(object sender, WebBrowserNewWindow2EventArgs e)
        {
            this.Navigate(this.beforeurl_);
            e.Cancel = true;
        }

    }
}