C#中判断本地系统的网络连接状态的方法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace ConsoleApplication1
{
    class Program
    {
        private const int INTERNET_CONNECTION_MODEM = 1;

        private const int INTERNET_CONNECTION_LAN = 2;

        private const int INTERNET_CONNECTION_PROXY = 4;

        private const int INTERNET_CONNECTION_MODEM_BUSY = 8;

        [DllImport("winInet.dll ")]

        //声明外部的函数：

        private static extern bool InternetGetConnectedState(
            ref  int Flag,
            int dwReserved
        );

        static void Main(string[] args)
        {
            int Flag = 0;

            string netStates = "";

            if (!InternetGetConnectedState(ref Flag, 0))
            {
                Console.WriteLine("no！");
            }
            else
            {

                if ((Flag & INTERNET_CONNECTION_MODEM) != 0)

                    netStates += " Connect by MODEM /n";

                if ((Flag & INTERNET_CONNECTION_LAN) != 0)

                    netStates += "Connect by LAN  /n";

                if ((Flag & INTERNET_CONNECTION_PROXY) != 0)

                    netStates += "Connect by PROXY /n";

                if ((Flag & INTERNET_CONNECTION_MODEM_BUSY) != 0)

                    netStates += " MODEM is busy  /n";

            }

            Console.WriteLine(netStates);
            Console.ReadLine();
        }
    }
}