在C#中可以使用多种方法来判断网络的连接状态，比如使用WIN32的API来判断，也可以直接Ping某个网址来判断。

下面来介绍下我最进行写的一个判断网络连接的方法类，使用了Wine32的API函数与Ping.Send结合的方法，代码如下：

using System;

using System.Collections.Generic;

using System.Text;

using System.Runtime.InteropServices;

using System.Net.NetworkInformation;

namespace TestNetConnectWin32

{

    public class GetInternetConStatus

    {

        private const int INTERNET_CONNECTION_MODEM = 1;

        private const int INTERNET_CONNECTION_LAN = 2;

        [DllImport("winInet.dll")]

        private static extern bool InternetGetConnectedState(

        ref   int dwFlag,

        int dwReserved

        );

        /// <summary>

        /// 判断网络的连接状态

        /// </summary>

        /// <returns>

        /// 网络状态(1-->未联网;2-->采用调治解调器上网;3-->采用网卡上网)

        ///</returns>

        public static int GetNetConStatus(string strNetAddress)

        {

            int iNetStatus = 0;

            System.Int32 dwFlag = new int();

            if (!InternetGetConnectedState(ref dwFlag, 0))

            {  

                //没有能连上互联网

                iNetStatus = 1;

            }

            else if ((dwFlag & INTERNET_CONNECTION_MODEM) != 0)

            {

                //采用调治解调器上网,需要进一步判断能否登录具体网站

                if (PingNetAddress(strNetAddress))

                {

                    //可以ping通给定的网址,网络OK

                    iNetStatus = 2;

                }

                else

                {

                    //不可以ping通给定的网址,网络不OK

                    iNetStatus = 4;

                }

            }

            

            else if ((dwFlag & INTERNET_CONNECTION_LAN) != 0)

            {

                //采用网卡上网,需要进一步判断能否登录具体网站

                if (PingNetAddress(strNetAddress))

                {

                    //可以ping通给定的网址,网络OK

                    iNetStatus = 3;

                }

                else

                {

                    //不可以ping通给定的网址,网络不OK

                    iNetStatus = 5;

                }

            }

            return iNetStatus;

        }

        /// <summary>

        /// ping 具体的网址看能否ping通

        /// </summary>

        /// <param name="strNetAdd"></param>

        /// <returns></returns>

        private static bool PingNetAddress(string strNetAdd)

        {

            bool Flage = false;

            Ping ping = new Ping();

            try

            {

                PingReply pr = ping.Send(strNetAdd, 3000);

                if (pr.Status == IPStatus.TimedOut)

                {

                    Flage = false;

                }

                if (pr.Status == IPStatus.Success)

                {

                    Flage = true;

                }

                else

                {

                    Flage = false;

                }

            }

            catch

            {

                Flage = false;

            }

            return Flage;

        }

    }

}

//判断方法

 private void btnJudge_Click(object sender, EventArgs e)

        {

            int iNetStatus = GetInternetConStatus.GetNetConStatus("baidu.com");

            if (iNetStatus == 1)

            {

                lblNetStatus.Text = "网络未连接";

            }

            else if(iNetStatus==2)

            {

                lblNetStatus.Text = "采用调治解调器上网";

            }

            else if (iNetStatus == 3)

            {

                lblNetStatus.Text = "采用网卡上网";

            }

            else if (iNetStatus == 4)

            {

                lblNetStatus.Text = "采用调治解调器上网,但是联不通指定网络";

            }

            else if (iNetStatus == 5)

            {

                lblNetStatus.Text = "采用网卡上网,但是联不通指定网络";

            }

        }