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.
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;
}
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;
}
}
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.
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;
}
}
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。
