c#使用winnet检测网络连接状况

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

    class NetStatus
    {
        private const long INTERNET_CONNECTION_MODEM = 1;//Local system uses a modem to connect to the Internet.

        private const long INTERNET_CONNECTION_LAN = 2; //Local system uses a local area network to connect to the Internet.

        private const long INTERNET_CONNECTION_PROXY = 4;//Local system uses a proxy server to connect to the Internet.

        private const long INTERNET_CONNECTION_MODEM_BUSY = 8;   //No longer used.

        private const long INTERNET_CONNECTION_CONFIGURED = 64; //Local system has a valid connection to the Internet, but it might or might not be currently connected.

        private const long INTERNET_CONNECTION_OFFLINE = 32; // Local system is in offline mode.

        private const long INTERNET_RAS_INSTALLED = 16; //Local system has RAS installed.

        [DllImport("wininet.dll")]

        public static extern bool InternetGetConnectedState(out   long lpdwFlags, long dwReserved);
        public static string NetCheck()
        {
            long lfag;
            string strConnectionDev = "";

            if (InternetGetConnectedState(out lfag, 0))
                strConnectionDev = "网络连接正常!";
            else
                strConnectionDev = "网络连接不可用!";

            if ((lfag & INTERNET_CONNECTION_OFFLINE) > 0)
                strConnectionDev += "OFFLINE 本地系统处于离线模式。";

            if ((lfag & INTERNET_CONNECTION_MODEM) > 0)
                strConnectionDev += "Modem 本地系统使用调制解调器连接到互联网。";

            if ((lfag & INTERNET_CONNECTION_LAN) > 0)
                strConnectionDev += "LAN 本地系统使用的局域网连接到互联网。";

            if ((lfag & INTERNET_CONNECTION_PROXY) > 0)
                strConnectionDev += "a   Proxy";

            if ((lfag & INTERNET_CONNECTION_MODEM_BUSY) > 0)
                strConnectionDev += "Modem   but   modem   is   busy";

            return strConnectionDev;
        } 
    }