C# 示例：檢測網路連線
我們的應用程式的某些功能，可能需要一個網際網路連線的執行時間測試。一旦檢測到網際網路連線，可能會暫時被禁用的功能需要訪問Internet和/或使用者可以通過警報訊息通知。否則，應用程式可能會導致在操作過程中的錯誤，否則可能會導致惱人的問題.
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.
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.
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.
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 noNetworkInformationnamespace 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 address208.69.34.231. We could use Google’s web addresswww.google.com:
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.
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)
WinINetAPI provides functions to test internet connectivity, such asInternetCheckConnectionandInternetGetConnectedState. I do not have any idea about what these fucntions do exactly to test internet connectivity. You may refer tohttp://msdn.microsoft.com/en-us/library/aa384346(v=VS.85).aspxandhttp://msdn.microsoft.com/en-us/library/aa384702(v=VS.85).aspxfor details.
An example usage can be:
[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); }
1. win32 API函式的做法:
要用的函式：InternetGetConnectedState
函式原形：BOOL InternetGetConnectedState(LPDWORD lpdwFlags,DWORD dwReserved);
引數lpdwFlags返回當前網路狀態,，引數dwReserved依然是保留引數，設定為0即可。
INTERNET_CONNECTION_MODEM 通過調治解調器連線網路
INTERNET_CONNECTION_LAN 通過區域網連線網路
這個函式的功能是很強的。它可以：
1. 判斷網路連線是通過網絡卡還是通過調治解調器
2. 是否通過代理上網
3. 判斷連線是On Line還是Off Line
4. 判斷是否安裝“撥號網路服務”
5. 判斷調治解調器是否正在使用
這個win32 API在系統system32資料夾中wininet.dll中
使用這個判斷的話,需要在類中這樣寫:
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("未連網!");
}
else if ((dwFlag & INTERNET_CONNECTION_MODEM) != 0)
{
MessageBox.Show("採用調治解調器上網!");
}
else if((dwFlag & INTERNET_CONNECTION_LAN)!=0)
{
MessageBox.Show("採用網絡卡上網!");
}
}
}
}
2. 採用PING的方法 ping一個常見域名，如果ping通則網路正常
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();//建立Ping物件p
PingReply pr = p.Send("10.13.88.111");//向指定IP或者主機名的計算機發送ICMP協議的ping資料包
if (pr.Status == IPStatus.Success)//如果ping成功
{
Console.WriteLine("網路連線成功, 執行下面任務...");
}
else
{
int times = 0;//重新連線次數;
do
{
if (times >= 12)
{
Console.WriteLine("重新嘗試連線超過12次,連線失敗程式結束");
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("連線成功");
times = 0;//連線成功，重新連線次數清為0;
}
}
}
}
一個完整的示例
ASP.net網站程式執行的時候，某些情況下需要判斷網路的連通狀態，包括區域網、網際網路、aol等，甚至某個具體網站的連通情況。以下類庫可以實現聯網狀態檢測：
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方式獲取網路連結狀態
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>
/// 在指定時間內嘗試連線指定主機上的指定埠。 （預設埠：80,預設連結超時：5000毫秒）
/// </summary>
/// <param name="HostNameOrIp">主機名稱或者IP地址</param>
/// <param name="port">埠</param>
/// <param name="timeOut">超時時間</param>
/// <returns>返回布林型別</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>
/// 在指定時間內嘗試連線指定主機上的指定埠。 （預設埠：80,預設連結超時：5000毫秒）
/// </summary>
/// <param name= "hostname ">要連線到的遠端主機的 DNS 名。</param>
/// <param name= "port ">要連線到的遠端主機的埠號。 </param>
/// <param name= "millisecondsTimeout ">要等待的毫秒數，或 -1 表示無限期等待。</param>
/// <returns>已連線的一個 TcpClient 例項。</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);//不推薦使用（無法實際控制超時時間）
bool IsHostAlive;
TcpClient tc = TcpClientConnector.Connect("hk.yahoo.com", null, null);//推薦使用（採用執行緒池強行中斷超時時間）
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 + " 耗時：" + ts1.TotalMilliseconds + "<br />");
Response.Write("TcpClient（hk.yahoo.com）：" + IsHostAlive + " 耗時：" + ts2.TotalMilliseconds + "<br />");
}
}
}
執行效果：
Connect：True
Lan：True
Wan：True
Aol：True
Sip（cn.yahoo.com）：True 耗時：265.625
TcpClient（hk.yahoo.com）：False 耗時：5000
當然，以上類庫也可以在C#windows程式中使用。