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Check for internet connection

Thursday, August 30, 2007 2:09 PM

Sometimes we can't trust networks or they may be unstable and our applications usually throw an unexpected error or the unusual occurs. Here is the snippet that I use to determine if the computer that the application is running on has an active internet connection. Note the use of unmanaged code.

   1: /// <summary>
   2: /// Performs actions on the network
   3: /// </summary>
   4: public class NetworkHandler
   5: {
   6:     // Extern Library
   7:     // UnManaged code - be careful.
   8:     [DllImport("wininet.dll")]
   9:     private extern static bool 
  10:         InternetGetConnectedState(out int Description, int ReservedValue);
  11:  
  12:     /// <summary>
  13:     /// Determines if there is an active connection on this computer
  14:     /// </summary>
  15:     /// <returns></returns>
  16:     public static bool HasActiveConnection()
  17:     {
  18:         try
  19:         {
  20:             int desc;
  21:             return InternetGetConnectedState(out desc, 0);
  22:         }
  23:         catch { }
  24:  
  25:         // If it gets here, then wininet.dll must have failed, so
  26:         // try resolving a host that is always going to be online such as google, microsoft
  27:         System.Uri Url = new System.Uri("http://www.google.com");
  28:         System.Net.WebRequest WebReq;
  29:         System.Net.WebResponse Resp;
  30:         WebReq = System.Net.WebRequest.Create(Url);
  31:         try
  32:         {
  33:             Resp = WebReq.GetResponse();
  34:             Resp.Close();
  35:             WebReq = null;
  36:             return true;
  37:         }
  38:         catch {}
  39:         finally
  40:         {
  41:             WebReq = null;
  42:         }
  43:  
  44:         // Oh, well we tried.
  45:         return false;
  46:     }
  47: }

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