C# 示例：检测网络连接

       我们的应用程序的某些功能，可能需要一个互联网连接的运行时间测试。 一旦检测到互联网连接，可能会暂时被禁用的功能需要访问Internet和/或用户可以通过警报消息通知。 否则，应用程序可能会导致在操作过程中的错误，否则可能会导致恼人的问题.

引用这里: https://www.codeproject.com/Tips/147662/Testing-Internet-Connectivity

Method 1: WebRequest

We may send a web request to a website which assumed to be online always, for example google.com. If we can get a response, then obviously the device that runs our application is connected to the internet.
 

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	public static bool WebRequestTest()
        {
            string url = "http://www.google.com";
            try
            {
                System.Net.WebRequest myRequest = System.Net.WebRequest.Create(url);
                System.Net.WebResponse myResponse = myRequest.GetResponse();
            }
            catch (System.Net.WebException)
            {
                return false;
            }
            return true;
        }

 

Method 2: TCP Socket

There can be some delay in response of web request therefore this method may not be fast enough for some applications. A better way is to check whether port 80, default port for http traffic, of an always online website.

 

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	public static bool TcpSocketTest()
        {
            try
            {
                System.Net.Sockets.TcpClient client =
                    new System.Net.Sockets.TcpClient("www.google.com", 80);
                client.Close();
                return true;
            }
            catch (System.Exception ex)
            {
                return false;
            }
        }

 

Method 3: Ping

There can be some delay in response of web request, therefore this method may not be fast enough for some applications. A better way is to check whether port 80, default port for http traffic, of an always online website.
 

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public bool PingTest()
        {
            System.Net.NetworkInformation.Ping ping = new System.Net.NetworkInformation.Ping();
 
            System.Net.NetworkInformation.PingReply pingStatus =
                ping.Send(IPAddress.Parse("208.69.34.231"),1000);
 
            if (pingStatus.Status == System.Net.NetworkInformation.IPStatus.Success)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

 

You cannot use this method in .NET Compact Framework because there is no NetworkInformation namespace that comes with Compact Framework. However, you can use Smart Device Framework (http://www.opennetcf.com[^], Community Edition is free for download) provided by OpenNETCF. This framework comes with many other useful tools that .NET Compact Framework does not contain.

 

Notice that I used Google’s IP address 208.69.34.231. We could use Google’s web address www.google.com:

 

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  System.Net.NetworkInformation.PingReply pingStatus = ping.Send("www.google.com",1000);

 

However, that will require DNS lookup which causes extra delay.

 

Method 4: DNS Lookup

Alternatively you can use DNS lookup to check internet connectivity. This method is faster than Ping method.
 

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	public static bool DnsTest()
        {
            try
            {
                System.Net.IPHostEntry ipHe =
                    System.Net.Dns.GetHostByName("www.google.com");
                return true;
            }
            catch
            {
                return false;
            }
        }

 

Method 5: Windows Internet API (WinINet)

WinINet API provides functions to test internet connectivity, such as InternetCheckConnection andInternetGetConnectedState. I do not have any idea about what these fucntions do exactly to test internet connectivity. You may refer to http://msdn.microsoft.com/en-us/library/aa384346(v=VS.85).aspx andhttp://msdn.microsoft.com/en-us/library/aa384702(v=VS.85).aspx for details.
 

An example usage can be:

 

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	[DllImport("wininet.dll")]
        private extern static bool InternetGetConnectedState(out int connDescription, int ReservedValue);
 
	//check if a connection to the Internet can be established 
        public static bool IsConnectionAvailable()
        {
            int Desc;
            return InternetGetConnectedState(out connDesc, 0);
        }

这个示例很好，自带监听网络状态：http://www.codeproject.com/Articles/64975/Detect-Internet-Network-Availability

1. win32 API函数的做法:

要用的函数：InternetGetConnectedState

函数原形：BOOL InternetGetConnectedState(LPDWORD lpdwFlags,DWORD dwReserved);

参数lpdwFlags返回当前网络状态,，参数dwReserved依然是保留参数，设置为0即可。

INTERNET_CONNECTION_MODEM 通过调治解调器连接网络

INTERNET_CONNECTION_LAN 通过局域网连接网络

这个函数的功能是很强的。它可以：

　　1. 判断网络连接是通过网卡还是通过调治解调器

　　2. 是否通过代理上网

　　3. 判断连接是On Line还是Off Line

　　4. 判断是否安装“拨号网络服务”

　　5. 判断调治解调器是否正在使用

这个win32 API在系统system32文件夹中wininet.dll中

使用这个判断的话,需要在类中这样写:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace API
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        
        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);

        private void button1_Click(object sender, EventArgs e)
        {
            System.Int32 dwFlag = new int();
            if (!InternetGetConnectedState(ref dwFlag, 0))
            {
                MessageBox.Show("未连网!");
            }
            else if ((dwFlag & INTERNET_CONNECTION_MODEM) != 0)
            {
                MessageBox.Show("采用调治解调器上网!");
            }
            else if((dwFlag & INTERNET_CONNECTION_LAN)!=0)   
            {
                MessageBox.Show("采用网卡上网!");  
            }
        }
    }
}

2. 采用PING的方法 ping一个常见域名，如果ping通则网络正常

using System;
using System.Collections.Generic;
using System.Text;
using System.Net.NetworkInformation;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Ping p = new Ping();//创建Ping对象p
            PingReply pr = p.Send("10.13.88.111");//向指定IP或者主机名的计算机发送ICMP协议的ping数据包

            if (pr.Status == IPStatus.Success)//如果ping成功
            {
                Console.WriteLine("网络连接成功, 执行下面任务...");
            }
            else
            {
                int times = 0;//重新连接次数;
                do
                {
                    if (times >= 12)
                    {
                        Console.WriteLine("重新尝试连接超过12次,连接失败程序结束");
                        return;
                    }

                    Thread.Sleep(1000);//等待

                    pr = p.Send("10.13.88.111");

                    Console.WriteLine(pr.Status);

                    times++;

                }
                while (pr.Status != IPStatus.Success);

                Console.WriteLine("连接成功");
                times = 0;//连接成功，重新连接次数清为0;
            }
        }
    }
}

 一个完整的示例

ASP.net网站程序运行的时候，某些情况下需要判断网络的连通状态，包括局域网、互联网、aol等，甚至某个具体网站的连通情况。以下类库可以实现联网状态检测：

 

using System;
using System.Web;
using System.Net.Sockets;
using System.Runtime.InteropServices;
using System.Threading;
 
namespace VvxT.Web
{
    public class Internet
    {
        #region 利用API方式获取网络链接状态
        private static int NETWORK_ALIVE_LAN = 0x00000001;
        private static int NETWORK_ALIVE_WAN = 0x00000002;
        private static int NETWORK_ALIVE_AOL = 0x00000004;
 
        [DllImport("sensapi.dll")]
        private extern static bool IsNetworkAlive(ref int flags);
        [DllImport("sensapi.dll")]
        private extern static bool IsDestinationReachable(string dest, IntPtr ptr);
 
        [DllImport("wininet.dll")]
        private extern static bool InternetGetConnectedState(out int connectionDescription, int reservedValue);
 
        public Internet() { }
 
        public static bool IsConnected()
        {
            int desc = 0;
            bool state = InternetGetConnectedState(out desc, 0);
            return state;
        }
 
        public static bool IsLanAlive()
        {
            return IsNetworkAlive(ref NETWORK_ALIVE_LAN);
        }
        public static bool IsWanAlive()
        {
            return IsNetworkAlive(ref NETWORK_ALIVE_WAN);
        }
        public static bool IsAOLAlive()
        {
            return IsNetworkAlive(ref NETWORK_ALIVE_AOL);
        }
        public static bool IsDestinationAlive(string Destination)
        {
            return (IsDestinationReachable(Destination, IntPtr.Zero));
        }
        #endregion
 
        /// <summary>
        /// 在指定时间内尝试连接指定主机上的指定端口。 （默认端口：80,默认链接超时：5000毫秒）
        /// </summary>
        /// <param name="HostNameOrIp">主机名称或者IP地址</param>
        /// <param name="port">端口</param>
        /// <param name="timeOut">超时时间</param>
        /// <returns>返回布尔类型</returns>
        public static bool IsHostAlive(string HostNameOrIp, int? port, int? timeOut)
        {
            TcpClient tc = new TcpClient();
            tc.SendTimeout = timeOut ?? 5000;
            tc.ReceiveTimeout = timeOut ?? 5000;
 
            bool isAlive;
            try
            {
                tc.Connect(HostNameOrIp, port ?? 80);
                isAlive = true;
            }
            catch
            {
                isAlive = false;
            }
            finally
            {
                tc.Close();
            }
            return isAlive;
        }
 
    }
 
    public class TcpClientConnector
    {
        /// <summary>
        /// 在指定时间内尝试连接指定主机上的指定端口。 （默认端口：80,默认链接超时：5000毫秒）
        /// </summary>
        /// <param name= "hostname ">要连接到的远程主机的 DNS 名。</param>
        /// <param name= "port ">要连接到的远程主机的端口号。 </param>
        /// <param name= "millisecondsTimeout ">要等待的毫秒数，或 -1 表示无限期等待。</param>
        /// <returns>已连接的一个 TcpClient 实例。</returns>
        public static TcpClient Connect(string hostname, int? port, int? millisecondsTimeout)
        {
            ConnectorState cs = new ConnectorState();
            cs.Hostname = hostname;
            cs.Port = port ?? 80;
            ThreadPool.QueueUserWorkItem(new WaitCallback(ConnectThreaded), cs);
            if (cs.Completed.WaitOne(millisecondsTimeout ?? 5000, false))
            {
                if (cs.TcpClient != null) return cs.TcpClient;
                return null;
                //throw cs.Exception;
            }
            else
            {
                cs.Abort();
                return null;
                //throw new SocketException(11001); // cannot connect
            }
        }
 
        private static void ConnectThreaded(object state)
        {
            ConnectorState cs = (ConnectorState)state;
            cs.Thread = Thread.CurrentThread;
            try
            {
                TcpClient tc = new TcpClient(cs.Hostname, cs.Port);
                if (cs.Aborted)
                {
                    try { tc.GetStream().Close(); }
                    catch { }
                    try { tc.Close(); }
                    catch { }
                }
                else
                {
                    cs.TcpClient = tc;
                    cs.Completed.Set();
                }
            }
            catch (Exception e)
            {
                cs.Exception = e;
                cs.Completed.Set();
            }
        }
 
        private class ConnectorState
        {
            public string Hostname;
            public int Port;
            public volatile Thread Thread;
            public readonly ManualResetEvent Completed = new ManualResetEvent(false);
            public volatile TcpClient TcpClient;
            public volatile Exception Exception;
            public volatile bool Aborted;
            public void Abort()
            {
                if (Aborted != true)
                {
                    Aborted = true;
                    try { Thread.Abort(); }
                    catch { }
                }
            }
        }
    }
}
 

使用方法：Default.aspx.cs

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net.Sockets;
 
namespace VvxT.Web
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            bool IsConnected = Internet.IsConnected();
            bool IsAOLAlive = Internet.IsAOLAlive();
 
            DateTime oldTime1 = DateTime.Now;
            bool IsDestinationAlive = Internet.IsDestinationAlive("cn.yahoo.com");
            DateTime newTime1 = DateTime.Now;
            TimeSpan ts1 = newTime1 - oldTime1;
 
            bool IsLanAlive = Internet.IsLanAlive();
            bool IsWanAlive = Internet.IsWanAlive();
 
            DateTime oldTime2 = DateTime.Now;
            //bool IsHostAlive = Internet.IsHostAlive("hk.yahoo.com", null, null);//不推荐使用（无法实际控制超时时间）
            bool IsHostAlive;
            TcpClient tc = TcpClientConnector.Connect("hk.yahoo.com", null, null);//推荐使用（采用线程池强行中断超时时间）
            try
            {
                if (tc != null)
                {
                    tc.GetStream().Close();
                    tc.Close();
                    IsHostAlive = true;
                }
                else
                    IsHostAlive = false;
            }
            catch { IsHostAlive = false; }
            DateTime newTime2 = DateTime.Now;
            TimeSpan ts2 = newTime2 - oldTime2;
 
            Response.Write("Connect：" + IsConnected + "<br />");
            Response.Write("Lan：" + IsLanAlive + "<br />");
            Response.Write("Wan：" + IsWanAlive + "<br />");
            Response.Write("Aol：" + IsAOLAlive + "<br />");
            Response.Write("Sip（cn.yahoo.com）：" + IsDestinationAlive + " 耗时：" + ts1.TotalMilliseconds + "<br />");
            Response.Write("TcpClient（hk.yahoo.com）：" + IsHostAlive + " 耗时：" + ts2.TotalMilliseconds + "<br />");
 
 
        }
    }
}
 
运行效果：
Connect：True
Lan：True
Wan：True
Aol：True
Sip（cn.yahoo.com）：True 耗时：265.625
TcpClient（hk.yahoo.com）：False 耗时：5000
 
当然，以上类库也可以在C#windows程序中使用。