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Dns.BeginResolve Method

NOTE: This method is now obsolete.

Begins an asynchronous request to resolve a DNS host name or IP address to an IPAddress instance.

Namespace: System.Net
Assembly: System (in system.dll)

'Declaration
<ObsoleteAttribute("BeginResolve is obsoleted for this type, please use BeginGetHostEntry instead. http://go.microsoft.com/fwlink/?linkid=14202")> _
Public Shared Function BeginResolve ( _
	hostName As String, _
	requestCallback As AsyncCallback, _
	stateObject As Object _
) As IAsyncResult
'Usage
Dim hostName As String
Dim requestCallback As AsyncCallback
Dim stateObject As Object
Dim returnValue As IAsyncResult

returnValue = Dns.BeginResolve(hostName, requestCallback, stateObject)
/** @attribute ObsoleteAttribute("BeginResolve is obsoleted for this type, please use BeginGetHostEntry instead. http://go.microsoft.com/fwlink/?linkid=14202") */ 
public static IAsyncResult BeginResolve (
	String hostName, 
	AsyncCallback requestCallback, 
	Object stateObject
)
ObsoleteAttribute("BeginResolve is obsoleted for this type, please use BeginGetHostEntry instead. http://go.microsoft.com/fwlink/?linkid=14202") 
public static function BeginResolve (
	hostName : String, 
	requestCallback : AsyncCallback, 
	stateObject : Object
) : IAsyncResult

Parameters

hostName

The DNS name of the host.

requestCallback

An AsyncCallback delegate that references the method to invoke when the operation is complete.

stateObject

A user-defined object that contains information about the operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

An IAsyncResult instance that references the asynchronous request.

Exception typeCondition

ArgumentNullException

hostName is a null reference (Nothing in Visual Basic).

SocketException

The caller does not have permission to access DNS information.

The asynchronous BeginResolve operation must be completed by calling the EndResolve method. Typically, the method is invoked by the requestCallback delegate.

This method does not block until the operation is complete. To block until the operation is complete, use the Resolve method.

For more information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.

NoteNote

This member emits trace information when you enable network tracing in your application. For more information, see Network Tracing.

The following example uses BeginResolve to resolve a DNS host name to an IPAddress.

Class DnsBeginGetHostByName
    
    Class RequestState
        Public host As IPHostEntry
        
        Public Sub New()
            host = Nothing
        End Sub 'New
    End Class 'RequestState
    
    
    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 'Main
    
    
    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 'RespCallback

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

    static class RequestState
    {
        public IPHostEntry host;

        public RequestState()
        {
            host = null;
        } //RequestState
    } //RequestState

    public static void main(String[] args)
    {
        allDone = new ManualResetEvent(false);        
        
        // Create an instance of the RequestState class.
        RequestState myRequestState = new DnsBeginGetHostByName.
            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.get_HostName());
        Console.WriteLine("\nIP address list : ");
        for (int index = 0; index < myRequestState.host.
            get_AddressList().length; index++) {
            Console.WriteLine(myRequestState.host.get_AddressList().
                get_Item(index));
        }
        Console.WriteLine("\nAliases : ");
        for (int index = 0; index < myRequestState.host.get_Aliases().
            length; index++) {
            Console.WriteLine(myRequestState.host.get_Aliases().
                get_Item(index));
        }
    } //main

    private static void RespCallback(IAsyncResult ar)
    {
        try {
            // Convert the IAsyncResult object to a RequestState object.
            RequestState tempRequestState = (RequestState)ar.get_AsyncState();

            // End the asynchronous request.
            tempRequestState.host = Dns.EndResolve(ar);
            allDone.Set();
        }
        catch (ArgumentNullException e) {
            Console.WriteLine("ArgumentNullException caught!!!");
            Console.WriteLine("Source : " + e.get_Source());
            Console.WriteLine("Message : " + e.get_Message());
        }
        catch (System.Exception e) {
            Console.WriteLine("Exception caught!!!");
            Console.WriteLine("Source : " + e.get_Source());
            Console.WriteLine("Message : " + e.get_Message());
        }
    } //RespCallback
} //DnsBeginGetHostByName

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 1.0, 1.1
Obsolete (compiler warning) in 2.0

.NET Compact Framework

Supported in: 1.0
Obsolete (compiler warning) in 2.0

Reference

Dns Class
Dns Members
System.Net Namespace

Other Resources

Asynchronous Calls

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