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WebRequest.BeginGetRequestStream Method

When overridden in a descendant class, provides an asynchronous version of the GetRequestStream method.

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

'Declaration
<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _
Public Overridable Function BeginGetRequestStream ( _
	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.BeginGetRequestStream(callback, _
	state)

Parameters

callback
Type: System.AsyncCallback

The AsyncCallback delegate.

state
Type: System.Object

An object containing state information for this asynchronous request.

Return Value

Type: System.IAsyncResult
An IAsyncResult that references the asynchronous request.

ExceptionCondition
NotImplementedException

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

NoteNote:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The BeginGetRequestStream method starts an asynchronous request for a stream used to send data to an Internet resource. The callback method that implements the AsyncCallback delegate uses the EndGetRequestStream method to return the request stream.

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.

The following example uses the BeginGetRequestStream to asynchronously obtain the request stream.

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

Public Class RequestState
    ' This class stores the request state of the request. 
    Public request As WebRequest

    Public Sub New()
        request = Nothing 
    End Sub ' New 
End Class ' RequestState


Class WebRequest_BeginGetRequeststream
    Public Shared allDone As New ManualResetEvent(False)

    Shared Sub Main()
          ' Create a new request. 
            Dim myWebRequest As WebRequest = WebRequest.Create("http://www.contoso.com/codesnippets/next.asp")
 ' Create an instance of the RequestState and assign  
            ' myWebRequest' to it's request field. 
            Dim myRequestState As New RequestState()
            myRequestState.request = myWebRequest
            myWebRequest.ContentType = "application/x-www-form-urlencoded" 

            ' Set the 'Method' property  to 'POST' to post data to a Uri.
            myRequestState.request.Method = "POST" 
            ' Start the asynchronous 'BeginGetRequestStream' method call. 
            Dim r As IAsyncResult = CType(myWebRequest.BeginGetRequestStream(AddressOf ReadCallback, myRequestState), IAsyncResult)
            ' Pause the current thread until the async operation completes.
            allDone.WaitOne()
            ' Send the Post and get the response. 
            Dim myWebResponse As WebResponse = myWebRequest.GetResponse()
            Console.WriteLine(ControlChars.Cr + "The string has been posted.")
            Console.WriteLine("Please wait for the response....")
            Dim streamResponse As Stream = myWebResponse.GetResponseStream()
            Dim streamRead As New StreamReader(streamResponse)
            Dim readBuff(256) As [Char]
            Dim count As Integer = streamRead.Read(readBuff, 0, 256)
            Console.WriteLine(ControlChars.Cr + "The contents of the HTML page are ")
            While count > 0
                Dim outputData As New [String](readBuff, 0, count)
                Console.WriteLine(outputData)
                count = streamRead.Read(readBuff, 0, 256)
            End While 

           ' Close the Stream Object.
            streamResponse.Close()
            streamRead.Close()
            ' Release the HttpWebResponse Resource.
             myWebResponse.Close()
    End Sub ' Main

    Private Shared Sub ReadCallback(asynchronousResult As IAsyncResult)
            Dim myRequestState As RequestState = CType(asynchronousResult.AsyncState, RequestState)
            Dim myWebRequest As WebRequest = myRequestState.request
            ' End the request. 
            Dim streamResponse As Stream = myWebRequest.EndGetRequestStream(asynchronousResult)
            ' Create a string that is to be posted to the uri.
            Console.WriteLine(ControlChars.Cr + "Please enter a string to be posted:")
            Dim postData As String = Console.ReadLine()
            Dim encoder As New ASCIIEncoding()
            ' Convert  the string into a byte array. 
            Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData)
            ' Write the data to the stream.
            streamResponse.Write(byteArray, 0, postData.Length)
            streamResponse.Close()
            ' Allow the main thread to resume.
            allDone.Set()
    End Sub ' ReadCallback 
End Class ' WebRequest_BeginGetRequeststream 
#using <mscorlib.dll>
#using <System.dll>
using namespace System;
using namespace System::Net;
using namespace System::IO;
using namespace System::Text;
using namespace System::Threading;

public __gc class RequestState {
   // This class stores the request state of the request.
public:
   WebRequest*  request;

   RequestState() {
      request = 0;
   }
};

__gc class WebRequest_BeginGetRequeststream {
public:
   static ManualResetEvent* allDone = new ManualResetEvent(false);
   static void ReadCallback(IAsyncResult* asynchronousResult) {

         RequestState* myRequestState =
            dynamic_cast<RequestState*> (asynchronousResult->AsyncState);
         WebRequest*  myWebRequest = myRequestState->request;

         // End of the Asynchronus request.
         Stream* streamResponse =
            myWebRequest->EndGetRequestStream(asynchronousResult);

         // Create a string that is to be posted to the uri.
         Console::WriteLine(S"Please enter a string to be posted:");
         String* postData=Console::ReadLine();
         // Convert  the string into a Byte array.
         Byte byteArray[] = Encoding::UTF8->GetBytes(postData);

         // Write data to the stream.
         streamResponse->Write(byteArray, 0, postData->Length);
         streamResponse->Close();
         allDone->Set();

   }
};

int main() {

      // Create a new request to the mentioned URL.
      WebRequest* myWebRequest= WebRequest::Create(S"http://www.contoso.com");

      // Create an instance of the RequestState and assign 'myWebRequest' to its request field.
      RequestState* myRequestState = new RequestState();
      myRequestState->request = myWebRequest;
      myWebRequest->ContentType=S"application/x-www-form-urlencoded";

      // Set the 'Method' prperty  to 'POST' to post data to a Uri.
      myRequestState->request->Method=S"POST";

      // Start the Asynchronous 'BeginGetRequestStream' method call.
      IAsyncResult* r = 
         dynamic_cast<IAsyncResult*> (myWebRequest->BeginGetRequestStream(new AsyncCallback(r, 
         WebRequest_BeginGetRequeststream::ReadCallback), myRequestState));

      WebRequest_BeginGetRequeststream::allDone->WaitOne();
      WebResponse* myWebResponse = myWebRequest->GetResponse();
      Console::WriteLine(S"The String* entered has been posted.");
      Console::WriteLine(S"Please wait for the response...");

      Stream* streamResponse = myWebResponse->GetResponseStream();
      StreamReader* streamRead = new StreamReader(streamResponse);
      Char readBuff[] = new Char[256];
      int count = streamRead->Read(readBuff, 0, 256);
      Console::WriteLine(S"The contents of the HTML page are ");

      while (count > 0) {
         String* outputData = new String(readBuff, 0, count);
         Console::Write(outputData);
         count = streamRead->Read(readBuff, 0, 256);
      }
      // Close the Stream Object.
      streamResponse->Close();
      streamRead->Close();

      // Release the HttpWebResponse Resource.
      myWebResponse->Close();
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

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