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WebRequest.BeginGetResponse Method

When overridden in a descendant class, begins an asynchronous request for an Internet resource.

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

'Declaration
Public Overridable Function BeginGetResponse ( _
	callback As AsyncCallback, _
	state As Object _
) As IAsyncResult
'Usage
Dim instance As WebRequest
Dim callback As AsyncCallback
Dim state As Object
Dim returnValue As IAsyncResult

returnValue = instance.BeginGetResponse(callback, state)
public IAsyncResult BeginGetResponse (
	AsyncCallback callback, 
	Object state
)
public function BeginGetResponse (
	callback : AsyncCallback, 
	state : Object
) : IAsyncResult
Not applicable.

Parameters

callback

The AsyncCallback delegate.

state

An object containing state information for this asynchronous request.

Return Value

An IAsyncResult that references the asynchronous request.

Exception typeCondition

NotImplementedException

Any attempt is made to access the method, when the method is not overridden in a descendant class.

The BeginGetResponse method starts an asynchronous request for a response. The callback method that implements the AsyncCallback delegate uses the EndGetResponse method to return the WebResponse from the Internet resource.

NoteNote:

The WebRequest class is an abstract class. The actual behavior of WebRequest instances at run time is determined by the descendant class returned by the WebRequest.Create method. For more information about default values and exceptions, see the documentation for the descendant classes, such as HttpWebRequest and FileWebRequest.

NoteNote:

If a WebException is thrown, use the Response and Status properties of the exception to determine the response from the server.

The following example uses BeginGetResponse to asynchronously request the target resource. When the resource has been obtained, the specified callback method will be executed.


Imports System
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
Imports Microsoft.VisualBasic



Public Class RequestState
  ' This class stores the state of the request
  Private Shared BUFFER_SIZE As Integer = 1024
  Public requestData As StringBuilder
  Public bufferRead() As Byte
  Public request As WebRequest
  Public response As WebResponse
  Public responseStream As Stream
  
  Public Sub New()
    bufferRead = New Byte(BUFFER_SIZE) {}
    requestData = New StringBuilder("")
    request = Nothing
    responseStream = Nothing
  End Sub ' New
End Class ' RequestState

Class WebRequest_BeginGetResponse
  Public Shared allDone As New ManualResetEvent(False)
  Private Shared BUFFER_SIZE As Integer = 1024
  
  Shared Sub Main()
    Try


      ' Create a new webrequest to the mentioned URL.
      Dim myWebRequest As WebRequest = WebRequest.Create("http://www.contoso.com")
      'Please, set the proxy to a correct value.
      Dim proxy As New WebProxy("itgproxy:80")
      proxy.Credentials = New NetworkCredential("srikun", "simrin123")
      myWebRequest.Proxy = proxy
      ' Create a new instance of the RequestState.
      Dim myRequestState As New RequestState()
      ' The 'WebRequest' object is associated to the 'RequestState' object.
      myRequestState.request = myWebRequest
      ' Start the Asynchronous call for response.
      Dim asyncResult As IAsyncResult = CType(myWebRequest.BeginGetResponse(AddressOf RespCallback, myRequestState), IAsyncResult)
      allDone.WaitOne()
	  ' Release the WebResponse resource.
	  myRequestState.response.Close()
      Console.Read()
    Catch e As WebException
      Console.WriteLine("WebException raised!")
      Console.WriteLine(ControlChars.Cr + "{0}", e.Message)
      Console.WriteLine(ControlChars.Cr + "{0}", e.Status)
    Catch e As Exception
      Console.WriteLine("Exception raised!")
      Console.WriteLine(("Source : " + e.Source))
      Console.WriteLine(("Message : " + e.Message))
    End Try
  End Sub ' Main

  Private Shared Sub RespCallback(asynchronousResult As IAsyncResult)
    Try
      ' Set the State of request to asynchronous.
      Dim myRequestState As RequestState = CType(asynchronousResult.AsyncState, RequestState)
      Dim myWebRequest1 As WebRequest = myRequestState.request
      ' End the Asynchronous response.
      myRequestState.response = myWebRequest1.EndGetResponse(asynchronousResult)
      ' Read the response into a 'Stream' object.
      Dim responseStream As Stream = myRequestState.response.GetResponseStream()
      myRequestState.responseStream = responseStream
      ' Begin the reading of the contents of the HTML page and print it to the console.
      Dim asynchronousResultRead As IAsyncResult = responseStream.BeginRead(myRequestState.bufferRead, 0, BUFFER_SIZE, AddressOf ReadCallBack, myRequestState)
    Catch e As WebException
      Console.WriteLine("WebException raised!")
      Console.WriteLine(ControlChars.Cr + "{0}", e.Message)
      Console.WriteLine(ControlChars.Cr + "{0}", e.Status)
    Catch e As Exception
      Console.WriteLine("Exception raised!")
      Console.WriteLine(("Source : " + e.Source))
      Console.WriteLine(("Message : " + e.Message))
    End Try
  End Sub ' RespCallback
  Private Shared Sub ReadCallBack(asyncResult As IAsyncResult)
    Try
      ' Result state is set to AsyncState.
      Dim myRequestState As RequestState = CType(asyncResult.AsyncState, RequestState)
      Dim responseStream As Stream = myRequestState.responseStream
      Dim read As Integer = responseStream.EndRead(asyncResult)
      ' Read the contents of the HTML page and then print to the console.
      If read > 0 Then
        myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.bufferRead, 0, read))
        Dim asynchronousResult As IAsyncResult = responseStream.BeginRead(myRequestState.bufferRead, 0, BUFFER_SIZE, AddressOf ReadCallBack, myRequestState)
      Else
        Console.WriteLine(ControlChars.Cr + "The HTML page Contents are:  ")
        If myRequestState.requestData.Length > 1 Then
          Dim sringContent As String
          sringContent = myRequestState.requestData.ToString()
          Console.WriteLine(sringContent)
        End If
        Console.WriteLine(ControlChars.Cr + "Press 'Enter' key to continue........")
        responseStream.Close()
	       allDone.Set()
      End If
    Catch e As WebException
      Console.WriteLine("WebException raised!")
      Console.WriteLine(ControlChars.Cr + "{0}", e.Message)
      Console.WriteLine(ControlChars.Cr + "{0}", e.Status)
    Catch e As Exception
      Console.WriteLine("Exception raised!")
      Console.WriteLine("Source :{0} ", e.Source)
      Console.WriteLine("Message :{0} ", e.Message)
    End Try
  End Sub ' ReadCallBack 

End Class ' WebRequest_BeginGetResponse


import System.*;
import System.Net.*;
import System.IO.*;
import System.Text.*;
import System.Threading.*;

public class RequestState
{
    // This class stores the state of the request.
    private static final int BUFFER_SIZE = 1024;
    public StringBuilder requestData;
    public ubyte bufferRead[];
    public WebRequest request;
    public WebResponse response;
    public Stream responseStream;

    public RequestState()
    {
        bufferRead = new ubyte[BUFFER_SIZE];
        requestData = new StringBuilder("");
        request = null;
        responseStream = null;
    } //RequestState
} //RequestState

class WebRequest_BeginGetResponse
{
    public static ManualResetEvent allDone = new ManualResetEvent(false);
    private static final int BUFFER_SIZE = 1024;

    public static void main(String[] args)
    {
        try {
            // Create a new webrequest to the mentioned URL.   
            WebRequest myWebRequest = 
                WebRequest.Create("http://www.contoso.com");
            // Please, set the proxy to a correct value. 
            WebProxy proxy = new WebProxy("myproxy:80");

            proxy.set_Credentials(new NetworkCredential("srikun", "simrin123"));
            myWebRequest.set_Proxy(proxy);
            // Create a new instance of the RequestState.
            RequestState myRequestState = new RequestState();
            // The 'WebRequest' object is associated to the 'RequestState' object.
            myRequestState.request = myWebRequest;
            // Start the Asynchronous call for response.
            IAsyncResult asyncResult = (IAsyncResult)(myWebRequest.
                BeginGetResponse(new AsyncCallback(RespCallback),
                myRequestState));
            allDone.WaitOne();
            // Release the WebResponse resource.
            myRequestState.response.Close();
            Console.Read();
        }
        catch (WebException e) {
            Console.WriteLine("WebException raised!");
            Console.WriteLine("\n{0}", e.get_Message());
            Console.WriteLine("\n{0}", e.get_Status());
        }
        catch (System.Exception e) {
            Console.WriteLine("Exception raised!");
            Console.WriteLine("Source : " + e.get_Source());
            Console.WriteLine("Message : " + e.get_Message());
        }
    } //main

    private static void RespCallback(IAsyncResult asynchronousResult)
    {
        try {
            // Set the State of request to asynchronous.
            RequestState myRequestState = (RequestState)(
                asynchronousResult.get_AsyncState());
            WebRequest myWebRequest1 = myRequestState.request;
            // End the Asynchronous response.
            myRequestState.response = myWebRequest1.EndGetResponse(
                asynchronousResult);
            // Read the response into a 'Stream' object.
            Stream responseStream = myRequestState.response.GetResponseStream();
            myRequestState.responseStream = responseStream;
            // Begin the reading of the contents of the HTML page and print it 
            // to the console.
            IAsyncResult asynchronousResultRead = responseStream.BeginRead(
                myRequestState.bufferRead, 0, BUFFER_SIZE, new AsyncCallback(
                ReadCallBack), myRequestState);
        }
        catch (WebException e) {
            Console.WriteLine("WebException raised!");
            Console.WriteLine("\n{0}", e.get_Message());
            Console.WriteLine("\n{0}", e.get_Status());
        }
        catch (System.Exception e) {
            Console.WriteLine("Exception raised!");
            Console.WriteLine("Source : " + e.get_Source());
            Console.WriteLine("Message : " + e.get_Message());
        }
    } //RespCallback

    private static void ReadCallBack(IAsyncResult asyncResult)
    {
        try {
            // Result state is set to AsyncState.
            RequestState myRequestState = (RequestState)(
                asyncResult.get_AsyncState());
            Stream responseStream = myRequestState.responseStream;
            int read = responseStream.EndRead(asyncResult);
            // Read the contents of the HTML page and then print to the console.
            if (read > 0) {
                myRequestState.requestData.Append(Encoding.get_ASCII().
                    GetString(myRequestState.bufferRead, 0, read));
                IAsyncResult asynchronousResult = responseStream.BeginRead(
                    myRequestState.bufferRead, 0, BUFFER_SIZE,
                    new AsyncCallback(ReadCallBack), myRequestState);
            }
            else {
                Console.WriteLine("\nThe HTML page Contents are:  ");
                if (myRequestState.requestData.get_Length() > 1) {
                    String sringContent;
                    sringContent = myRequestState.requestData.ToString();
                    Console.WriteLine(sringContent);
                }
                Console.WriteLine("\nPress 'Enter' key to continue........");
                responseStream.Close();
                allDone.Set();
            }
        }
        catch (WebException e) {
            Console.WriteLine("WebException raised!");
            Console.WriteLine("\n{0}", e.get_Message());
            Console.WriteLine("\n{0}", e.get_Status());
        }
        catch (System.Exception e) {
            Console.WriteLine("Exception raised!");
            Console.WriteLine("Source : {0}", e.get_Source());
            Console.WriteLine("Message : {0}", e.get_Message());
        }
    } //ReadCallBack
} //WebRequest_BeginGetResponse

Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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