class DnsBeginGetHostByName
{   
   public static System.Threading.ManualResetEvent allDone = null;

   class RequestState
   {
      public IPHostEntry host;
      public RequestState()
      {
         host = null;
      }
   }

   public static void Main()
   {
     allDone = new ManualResetEvent(false);
     // Create an instance of the RequestState class.
     RequestState myRequestState = new RequestState();

     // Begin an asynchronous request for information like host name, IP addresses, or 
     // aliases for specified the specified URI.
     IAsyncResult asyncResult = Dns.BeginResolve("www.contoso.com", new AsyncCallback(RespCallback), myRequestState );

     // Wait until asynchronous call completes.
     allDone.WaitOne();
     Console.WriteLine("Host name : " + myRequestState.host.HostName);
     Console.WriteLine("\nIP address list : ");
     for(int index=0; index < myRequestState.host.AddressList.Length; index++)
     {
       Console.WriteLine(myRequestState.host.AddressList[index]);
     }      
     Console.WriteLine("\nAliases : ");
     for(int index=0; index < myRequestState.host.Aliases.Length; index++)
     {
       Console.WriteLine(myRequestState.host.Aliases[index]);
     }      
   }
   
   private static void RespCallback(IAsyncResult ar)
   {
     try 
     {
       // Convert the IAsyncResult object to a RequestState object.
       RequestState tempRequestState = (RequestState)ar.AsyncState;
       // End the asynchronous request.
       tempRequestState.host = Dns.EndResolve(ar);
       allDone.Set();
     }
       catch(ArgumentNullException e) 
     {
       Console.WriteLine("ArgumentNullException caught!!!");
       Console.WriteLine("Source : " + e.Source);
       Console.WriteLine("Message : " + e.Message);
     }   
     catch(Exception e)
     {
       Console.WriteLine("Exception caught!!!");
       Console.WriteLine("Source : " + e.Source);
       Console.WriteLine("Message : " + e.Message);
     }
   }
}

//引入命名空间
using System;
using System.Drawing;
using System.Net;
using System.Text;
using System.Windows.Forms;

class MainClass
{
   private static void Resolved(IAsyncResult ar)
   {
      string buffer;

      IPHostEntry iphe = Dns.EndResolve(ar);

      buffer = "Host name: " + iphe.HostName;
      Console.WriteLine(buffer);

      foreach(string alias in iphe.Aliases)
      {
         buffer = "Alias: " + alias;
         Console.WriteLine(buffer);
      }
      foreach(IPAddress addrs in iphe.AddressList)
      {
         buffer = "Address: " + addrs.ToString();
         Console.WriteLine(buffer);
      }
   }

   public static void Main()
   {
      AsyncCallback OnResolved;

      OnResolved = new AsyncCallback(Resolved);

      string addr = "www.java2s.com";
      Object state = new Object();

      Dns.BeginResolve(addr, OnResolved, state);
   }
}