WebRequest::BeginGetRequestStream Method (AsyncCallback^, Object^)

 

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

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

public:
[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
virtual IAsyncResult^ BeginGetRequestStream(
	AsyncCallback^ callback,
	Object^ 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.

Exception Condition
NotImplementedException

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

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.

System_CAPS_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.

#using <System.dll>

using namespace System;
using namespace System::Net;
using namespace System::IO;
using namespace System::Text;
using namespace System::Threading;
public ref class RequestState
{
public:

   // This class stores the request state of the request.
   WebRequest^ request;
   RequestState()
   {
      request = nullptr;
   }

};

ref class WebRequest_BeginGetRequeststream
{
public:
   static ManualResetEvent^ allDone = gcnew 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( "Please enter a string to be posted:" );
      String^ postData = Console::ReadLine();

      // Convert  the string into a Byte array.
      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( "http://www.contoso.com" );

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

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

   // Start the Asynchronous 'BeginGetRequestStream' method call.
   IAsyncResult^ r = dynamic_cast<IAsyncResult^>(myWebRequest->BeginGetRequestStream( gcnew AsyncCallback( WebRequest_BeginGetRequeststream::ReadCallback ), myRequestState ));
   WebRequest_BeginGetRequeststream::allDone->WaitOne();
   WebResponse^ myWebResponse = myWebRequest->GetResponse();
   Console::WriteLine( "The String* entered has been posted." );
   Console::WriteLine( "Please wait for the response..." );
   Stream^ streamResponse = myWebResponse->GetResponseStream();
   StreamReader^ streamRead = gcnew StreamReader( streamResponse );
   array<Char>^readBuff = gcnew array<Char>(256);
   int count = streamRead->Read( readBuff, 0, 256 );
   Console::WriteLine( "The contents of the HTML page are " );
   while ( count > 0 )
   {
      String^ outputData = gcnew String( readBuff,0,count );
      Console::Write( outputData );
      count = streamRead->Read( readBuff, 0, 256 );
   }

   streamResponse->Close();
   streamRead->Close();

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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