C#判断本地系统的网络连接状态

函数InternetGetConnectedState返回本地系统的网络连接状态。

语法：

BOOL InternetGetConnectedState(

__out LPDWORD lpdwFlags,

__in DWORD dwReserved

);

参数：

lpdwFlags[out]

指向一个变量，该变量接收连接描述内容。该参数在函数返回FLASE时仍可以返回一个有效的标记。该参数可以为下列值的一个或多个。

值	含义
INTERNET_CONNECTION_CONFIGURED0x40	Local system has a valid connection to the Internet, but it might or might not be currently connected.
INTERNET_CONNECTION_LAN 0x02	Local system uses a local area network to connect to the Internet.
INTERNET_CONNECTION_MODEM0x01	Local system uses a modem to connect to the Internet.
INTERNET_CONNECTION_MODEM_BUSY0x08	No longer used.
INTERNET_CONNECTION_OFFLINE 0x20	Local system is in offline mode.
INTERNET_CONNECTION_PROXY0x04	Local system uses a proxy server to connect to the Internet.
INTERNET_RAS_INSTALLED0x10	Local system has RAS installed.

dwReserved[in]

保留值。必须为0。

返回值：

当存在一个modem或一个LAN连接时，返回TRUE，当不存在internet连接或所有的连接当前未被激活时，返回false。

当该函数返回false时，程序可以调用GetLastError来接收错误代码。

示例：

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();
        }
    }
}