WebRequest.BeginGetRequestStream(AsyncCallback, Object) Method
Definition
Important
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When overridden in a descendant class, provides an asynchronous version of the GetRequestStream() method.
public:
abstract IAsyncResult ^ BeginGetRequestStream(AsyncCallback ^ callback, System::Object ^ state);
public:
virtual IAsyncResult ^ BeginGetRequestStream(AsyncCallback ^ callback, System::Object ^ state);
public abstract IAsyncResult BeginGetRequestStream (AsyncCallback callback, object state);
public virtual IAsyncResult BeginGetRequestStream (AsyncCallback? callback, object? state);
public virtual IAsyncResult BeginGetRequestStream (AsyncCallback callback, object state);
abstract member BeginGetRequestStream : AsyncCallback * obj -> IAsyncResult
abstract member BeginGetRequestStream : AsyncCallback * obj -> IAsyncResult
override this.BeginGetRequestStream : AsyncCallback * obj -> IAsyncResult
Public MustOverride Function BeginGetRequestStream (callback As AsyncCallback, state As Object) As IAsyncResult
Public Overridable Function BeginGetRequestStream (callback As AsyncCallback, state As Object) As IAsyncResult
Parameters
- callback
- AsyncCallback
The AsyncCallback delegate.
- state
- Object
An object containing state information for this asynchronous request.
Returns
An IAsyncResult that references the asynchronous request.
Exceptions
Any attempt is made to access the method, when the method is not overridden in a descendant class.
Examples
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();
}
using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;
public class RequestState
{
// This class stores the request state of the request.
public WebRequest request;
public RequestState()
{
request = null;
}
}
class WebRequest_BeginGetRequeststream
{
public static ManualResetEvent allDone= new ManualResetEvent(false);
static void 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 it's request field.
RequestState myRequestState = 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.
IAsyncResult r=(IAsyncResult) myWebRequest.BeginGetRequestStream(
new AsyncCallback(ReadCallback),myRequestState);
// Pause the current thread until the async operation completes.
Console.WriteLine("main thread waiting...");
allDone.WaitOne();
// Assign the response object of 'WebRequest' to a 'WebResponse' variable.
WebResponse myWebResponse = myWebRequest.GetResponse();
Console.WriteLine("The string has been posted.");
Console.WriteLine("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("\nThe 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();
}
private static void ReadCallback(IAsyncResult asynchronousResult)
{
RequestState myRequestState =(RequestState) asynchronousResult.AsyncState;
WebRequest myWebRequest = myRequestState.request;
// End the Asynchronous 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.
byte[] byteArray = Encoding.UTF8.GetBytes(postData);
// Write the data to the stream.
streamResponse.Write(byteArray,0,postData.Length);
streamResponse.Close();
allDone.Set();
}
}
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
Public Class RequestState
' This class stores the request state of the request.
Public request As WebRequest
Public Sub New()
request = Nothing
End Sub
End Class
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
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
End Class
Remarks
Caution
WebRequest
, HttpWebRequest
, ServicePoint
, and WebClient
are obsolete, and you shouldn't use them for new development. Use HttpClient instead.
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.
Note
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.