Class DnsBeginGetHostByName
    
    Class RequestState
        Public host As IPHostEntry
        
        Public Sub New()
            host = Nothing
        End Sub
    End Class
    
    
    Public Shared Sub Main()
     Try
        ' Create an instance of the RequestState class.
        Dim myRequestState As New RequestState()
        
        ' Begin an asynchronous request for information such as the host name, IP addresses, 
        ' or aliases for the specified URI.
        Dim asyncResult As IAsyncResult = CType(Dns.BeginResolve("www.contoso.com", AddressOf RespCallback, myRequestState),IAsyncResult)

        ' Wait until asynchronous call completes.
        While asyncResult.IsCompleted <> True
        End While
        
        Console.WriteLine(("Host name : " + myRequestState.host.HostName))
        Console.WriteLine(ControlChars.Cr + "IP address list : ")
        Dim index As Integer
        For index = 0 To myRequestState.host.AddressList.Length - 1
            Console.WriteLine(myRequestState.host.AddressList(index))
        Next index
        Console.WriteLine(ControlChars.Cr + "Aliases : ")

        For index = 0 To myRequestState.host.Aliases.Length - 1
            Console.WriteLine(myRequestState.host.Aliases(index))
        Next index
    catch e as Exception
            Console.WriteLine("Exception caught!!!")
            Console.WriteLine(("Source : " + e.Source))
            Console.WriteLine(("Message : " + e.Message))
    End Try
    End Sub
    
    
    Private Shared Sub RespCallback(ar As IAsyncResult)
        Try
            ' Convert the IAsyncResult object to a RequestState object.
            Dim tempRequestState As RequestState = CType(ar.AsyncState, RequestState)

            ' End the asynchronous request.
            tempRequestState.host = Dns.EndResolve(ar)
            Catch e As ArgumentNullException
            Console.WriteLine("ArgumentNullException caught!!!")
            Console.WriteLine(("Source : " + e.Source))
            Console.WriteLine(("Message : " + e.Message))
            Catch e As Exception
            Console.WriteLine("Exception caught!!!")
            Console.WriteLine(("Source : " + e.Source))
            Console.WriteLine(("Message : " + e.Message))
        End Try
    End Sub

' 导入命名空间
Imports System.Net
Imports System.Net.Sockets


Public Class Tester
    Public Shared Sub Main

        Dim myThread As Threading.Thread
        myThread = New Threading.Thread(AddressOf BeginResolveIP)
        myThread.Start()

    End Sub
    Private Shared Sub BeginResolveIP()
        Try
            Dim myAsyncCallback As New AsyncCallback(AddressOf GetIPList)


            Dim myIAsyncResult As IAsyncResult = Dns.BeginResolve("www.google.com", myAsyncCallback, Nothing)

            Do While Not myIAsyncResult.IsCompleted
                Threading.Thread.Sleep(10)
            Loop
            Threading.Thread.Sleep(2000)
        Catch ex As SocketException
            Console.WriteLine(ex.Message)
        End Try

    End Sub

    Private Shared Sub GetIPList(ByVal pIAsyncResult As IAsyncResult)
        Dim myIPHostEntry As IPHostEntry
        myIPHostEntry = Dns.EndResolve(pIAsyncResult)

        Dim myIPAddresses() As IPAddress = myIPHostEntry.AddressList
        Dim myIPAddress As IPAddress

        For Each myIPAddress In myIPAddresses
            Console.WriteLine(myIPAddress.ToString)
        Next
    End Sub

    
End Class