换用代理IP的Webbrowser方法

转自：http://www.cnblogs.com/pmars/archive/2012/06/28/2567599.html

用webbrowser做浏览器，换取代理IP是常用的功能，下面贴一段用到的换ip的代码！

public class MyWebBrowser : WebBrowser
    {
        [ComImport, Guid("34A715A0-6587-11D0-924A-0020AFC7AC4D"),
        InterfaceType(ComInterfaceType.InterfaceIsIDispatch),
        TypeLibType(TypeLibTypeFlags.FHidden)]
        public interface DWebBrowserEvents2
        {
            [DispId(271)]
            void NavigateError(
                [In, MarshalAs(UnmanagedType.IDispatch)] object pDisp,
                [In] ref object URL, [In] ref object frame,
                [In] ref object statusCode, [In, Out] ref bool cancel);
        }
        AxHost.ConnectionPointCookie cookie;
        MyWebBrowserEventHelper helper;
        public delegate void WebBrowserNavigateErrorEventHandler(object sender,
            WebBrowserNavigateErrorEventArgs e);

        [PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
        protected override void CreateSink()
        {
            base.CreateSink();
            // Create an instance of the client that will handle the event
            // and associate it with the underlying ActiveX control.
            helper = new MyWebBrowserEventHelper(this);
            cookie = new AxHost.ConnectionPointCookie(
                this.ActiveXInstance, helper, typeof(DWebBrowserEvents2));
        }
        [PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
        protected override void DetachSink()
        {
            // Disconnect the client that handles the event
            // from the underlying ActiveX control.
            if (cookie != null)
            {
                cookie.Disconnect();
                cookie = null;
            }
            base.DetachSink();
        }
        public event WebBrowserNavigateErrorEventHandler NavigateError;
        // Raises the NavigateError event.
        protected virtual void OnNavigateError(
            WebBrowserNavigateErrorEventArgs e)
        {
            if (this.NavigateError != null)
            {
                this.NavigateError(this, e);
            }
        }
        // Handles the NavigateError event from the underlying ActiveX 
        // control by raising the NavigateError event defined in this class.
        private class MyWebBrowserEventHelper :
            StandardOleMarshalObject, DWebBrowserEvents2
        {
            private MyWebBrowser parent;
            public MyWebBrowserEventHelper(MyWebBrowser parent)
            {
                this.parent = parent;
            }
            public void NavigateError(object pDisp, ref object url,
                ref object frame, ref object statusCode, ref bool cancel)
            {
                // Raise the NavigateError event.
                this.parent.OnNavigateError(
                    new WebBrowserNavigateErrorEventArgs(
                    (String)url, (String)frame, (Int32)statusCode, cancel));
            }
        }
    }
    public class WebBrowserNavigateErrorEventArgs : EventArgs
    {
        private String urlValue;
        private String frameValue;
        private Int32 statusCodeValue;
        private Boolean cancelValue;
        public WebBrowserNavigateErrorEventArgs(
            String url, String frame, Int32 statusCode, Boolean cancel)
        {
            urlValue = url;
            frameValue = frame;
            statusCodeValue = statusCode;
            cancelValue = cancel;
        }
        public String Url
        {
            get { return urlValue; }
            set { urlValue = value; }
        }
        public String Frame
        {
            get { return frameValue; }
            set { frameValue = value; }
        }
        public Int32 StatusCode
        {
            get { return statusCodeValue; }
            set { statusCodeValue = value; }
        }
        public Boolean Cancel
        {
            get { return cancelValue; }
            set { cancelValue = value; }
        }
    }

使用函数

[DllImport("wininet.dll", SetLastError = true)]
        private static extern bool InternetSetOption(IntPtr hInternet, int dwOption, IntPtr lpBuffer, int lpdwBufferLength);
        public struct Struct_INTERNET_PROXY_INFO
        {
            public int dwAccessType;
            public IntPtr proxy;
            public IntPtr proxyBypass;
        };
        private void RefreshIESettings(string strProxy)
        {
            const int INTERNET_OPTION_PROXY = 38;
            const int INTERNET_OPEN_TYPE_PROXY = 3;

            Struct_INTERNET_PROXY_INFO struct_IPI;

            // Filling in structure 
            struct_IPI.dwAccessType = INTERNET_OPEN_TYPE_PROXY;
            struct_IPI.proxy = Marshal.StringToHGlobalAnsi(strProxy);
            struct_IPI.proxyBypass = Marshal.StringToHGlobalAnsi("local");

            // Allocating memory 
            IntPtr intptrStruct = Marshal.AllocCoTaskMem(Marshal.SizeOf(struct_IPI));

            // Converting structure to IntPtr 
            Marshal.StructureToPtr(struct_IPI, intptrStruct, true);

            bool iReturn = InternetSetOption(IntPtr.Zero, INTERNET_OPTION_PROXY, intptrStruct, Marshal.SizeOf(struct_IPI));
        }