Around and About .NET World

  1 using System;
  2 using System.ComponentModel;
  3 using System.Threading;
  4 using System.Net;
  5 
  6 namespace System.Net.NetworkInformation
  7 {
  8     public delegate void InternetAvailabilityChangedEventHandler(object sender, InternetAvailabilityEventArgs e);
  9     
 10     public static class NetworkMonitor
 11     {
 12         private const string HOST = "http://www.microsoft.com";
 13 
 14         private static AsyncOperation operation;
 15         private static SendOrPostCallback internetAvailabilityCallback;
 16         private static bool internetAvailable;
 17         
 18         private static Timer checkConnection;
 19         private const int CHECK_CONNECTION_TIMEOUT = 5000;
 20 
 21         public static event InternetAvailabilityChangedEventHandler InternetAvailabilityChanged;
 22 
 23         static NetworkMonitor()
 24         {
 25             internetAvailable = false;
 26 
 27             operation = AsyncOperationManager.CreateOperation(null);
 28             internetAvailabilityCallback = new SendOrPostCallback(InternetAvailabilityHandler);
 29 
 30             //Attiva il timer che controlla la disponibilità della connessione.
 31             checkConnection = new Timer(new TimerCallback(IsConnectionAvailable), null, 1, CHECK_CONNECTION_TIMEOUT);
 32         }
 33 
 34         public static bool IsConnectionAvailable()
 35         {
 36             HttpWebRequest request = null;
 37             HttpWebResponse response = null;
 38             bool isAvailable = false;
 39 
 40             try
 41             {
 42                 request = (HttpWebRequest)HttpWebRequest.Create(HOST);
 43                 response = (HttpWebResponse)request.GetResponse();
 44 
 45                 if (response.StatusCode == HttpStatusCode.OK)
 46                 {
 47                     // HTTP = 200 - Internet connection available, server online
 48                     isAvailable = true;
 49                 }
 50             }
 51             catch (WebException)
 52             { }
 53             finally
 54             {
 55                 try
 56                 {
 57                     if (response != null)
 58                         response.Close();
 59                 }
 60                 catch { }
 61             }
 62 
 63             return isAvailable;
 64         }
 65 
 66         private static void IsConnectionAvailable(object stateInfo)
 67         {
 68             checkConnection.Change(Timeout.Infinite, Timeout.Infinite);
 69 
 70             bool isAvailable = IsConnectionAvailable();            
 71             if (isAvailable != internetAvailable)
 72             {
 73                 internetAvailable = isAvailable;
 74                 operation.Post(internetAvailabilityCallback, new InternetAvailabilityEventArgs(isAvailable));
 75             }
 76 
 77             checkConnection.Change(CHECK_CONNECTION_TIMEOUT, CHECK_CONNECTION_TIMEOUT);
 78         }
 79 
 80         private static void InternetAvailabilityHandler(object stateInfo)
 81         {
 82             if (InternetAvailabilityChanged != null)
 83                 InternetAvailabilityChanged(null, (InternetAvailabilityEventArgs)stateInfo);
 84         }
 85     }
 86 
 87     public class InternetAvailabilityEventArgs : EventArgs
 88     {
 89         private bool isAvailable;
 90         public bool IsAvailable
 91         {
 92             get { return isAvailable; }
 93         }
 94 
 95         public InternetAvailabilityEventArgs(bool isAvailable)
 96         {
 97             this.isAvailable = isAvailable;
 98         }
 99     }
100 }