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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));        }