WebRequest.BeginGetResponse(AsyncCallback, Object) Method
Important
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When overridden in a descendant class, begins an asynchronous request for an Internet resource.
public:
abstract IAsyncResult ^ BeginGetResponse(AsyncCallback ^ callback, System::Object ^ state);
public:
virtual IAsyncResult ^ BeginGetResponse(AsyncCallback ^ callback, System::Object ^ state);
public abstract IAsyncResult BeginGetResponse (AsyncCallback callback, object state);
public virtual IAsyncResult BeginGetResponse (AsyncCallback? callback, object? state);
public virtual IAsyncResult BeginGetResponse (AsyncCallback callback, object state);
abstract member BeginGetResponse : AsyncCallback * obj -> IAsyncResult
abstract member BeginGetResponse : AsyncCallback * obj -> IAsyncResult
override this.BeginGetResponse : AsyncCallback * obj -> IAsyncResult
Public MustOverride Function BeginGetResponse (callback As AsyncCallback, state As Object) As IAsyncResult
Public Overridable Function BeginGetResponse (callback As AsyncCallback, state As Object) As IAsyncResult
- callback
- AsyncCallback
The AsyncCallback delegate.
- state
- Object
An object containing state information for this asynchronous request.
An IAsyncResult that references the asynchronous request.
Any attempt is made to access the method, when the method is not overridden in a descendant class.
The following example uses BeginGetResponse to asynchronously request the target resource. When the resource has been obtained, the specified callback method will be executed.
#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
{
private:
// This class stores the state of the request.
literal int BUFFER_SIZE = 1024;
public:
StringBuilder^ requestData;
array<Byte>^bufferRead;
WebRequest^ request;
WebResponse^ response;
Stream^ responseStream;
RequestState()
{
bufferRead = gcnew array<Byte>(BUFFER_SIZE);
requestData = gcnew StringBuilder( "" );
request = nullptr;
responseStream = nullptr;
}
};
ref class WebRequest_BeginGetResponse
{
public:
static ManualResetEvent^ allDone = gcnew ManualResetEvent( false );
literal int BUFFER_SIZE = 1024;
static void RespCallback( IAsyncResult^ asynchronousResult )
{
try
{
// Set the State of request to asynchronous.
RequestState^ myRequestState = dynamic_cast<RequestState^>(asynchronousResult->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, gcnew AsyncCallback( ReadCallBack ), myRequestState );
}
catch ( WebException^ e )
{
Console::WriteLine( "WebException raised!" );
Console::WriteLine( "\n {0}", e->Message );
Console::WriteLine( "\n {0}", e->Status );
}
catch ( Exception^ e )
{
Console::WriteLine( "Exception raised!" );
Console::WriteLine( "Source : {0}", e->Source );
Console::WriteLine( "Message : {0}", e->Message );
}
}
static void ReadCallBack( IAsyncResult^ asyncResult )
{
try
{
// Result state is set to AsyncState.
RequestState^ myRequestState = dynamic_cast<RequestState^>(asyncResult->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::ASCII->GetString( myRequestState->bufferRead, 0, read ) );
IAsyncResult^ asynchronousResult = responseStream->BeginRead( myRequestState->bufferRead, 0, BUFFER_SIZE, gcnew AsyncCallback( ReadCallBack ), myRequestState );
}
else
{
Console::WriteLine( "\nThe HTML page Contents are: " );
if ( myRequestState->requestData->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->Message );
Console::WriteLine( "\n {0}", e->Status );
}
catch ( Exception^ e )
{
Console::WriteLine( "Exception raised!" );
Console::WriteLine( "Source : {0}", e->Source );
Console::WriteLine( "Message : {0}", e->Message );
}
}
};
int main()
{
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 = gcnew WebProxy( "myproxy:80" );
proxy->Credentials = gcnew NetworkCredential( "srikun","simrin123" );
myWebRequest->Proxy = proxy;
// Create a new instance of the RequestState.
RequestState^ myRequestState = gcnew RequestState;
// The 'WebRequest' object is associated to the 'RequestState' object.
myRequestState->request = myWebRequest;
// Start the Asynchronous call for response.
IAsyncResult^ asyncResult = dynamic_cast<IAsyncResult^>(myWebRequest->BeginGetResponse( gcnew AsyncCallback( WebRequest_BeginGetResponse::RespCallback ), myRequestState ));
WebRequest_BeginGetResponse::allDone->WaitOne();
// Release the WebResponse resource.
myRequestState->response->Close();
Console::Read();
}
catch ( WebException^ e )
{
Console::WriteLine( "WebException raised!" );
Console::WriteLine( "\n {0}", e->Message );
Console::WriteLine( "\n {0}", e->Status );
}
catch ( Exception^ e )
{
Console::WriteLine( "Exception raised!" );
Console::WriteLine( "Source : {0}", e->Source );
Console::WriteLine( "Message : {0}", e->Message );
}
}
using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;
public class RequestState
{
// This class stores the state of the request.
const int BUFFER_SIZE = 1024;
public StringBuilder requestData;
public byte[] bufferRead;
public WebRequest request;
public WebResponse response;
public Stream responseStream;
public RequestState()
{
bufferRead = new byte[BUFFER_SIZE];
requestData = new StringBuilder("");
request = null;
responseStream = null;
}
}
class WebRequest_BeginGetResponse
{
public static ManualResetEvent allDone= new ManualResetEvent(false);
const int BUFFER_SIZE = 1024;
static void Main()
{
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.Credentials=new NetworkCredential("srikun","simrin123");
myWebRequest.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.Message);
Console.WriteLine("\n{0}",e.Status);
}
catch(Exception e)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Source : " + e.Source);
Console.WriteLine("Message : " + e.Message);
}
}
private static void RespCallback(IAsyncResult asynchronousResult)
{
try
{
// Set the State of request to asynchronous.
RequestState myRequestState=(RequestState) asynchronousResult.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.Message);
Console.WriteLine("\n{0}",e.Status);
}
catch(Exception e)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Source : " + e.Source);
Console.WriteLine("Message : " + e.Message);
}
}
private static void ReadCallBack(IAsyncResult asyncResult)
{
try
{
// Result state is set to AsyncState.
RequestState myRequestState = (RequestState)asyncResult.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.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.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.Message);
Console.WriteLine("\n{0}",e.Status);
}
catch(Exception e)
{
Console.WriteLine("Exception raised!");
Console.WriteLine("Source : {0}" , e.Source);
Console.WriteLine("Message : {0}" , e.Message);
}
}
}
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
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
End Class
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
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
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
End Class
Atenție
WebRequest
, HttpWebRequest
, ServicePoint
, and WebClient
are obsolete, and you shouldn't use them for new development. Use HttpClient instead.
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.
Notă
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.
Notă
If a WebException is thrown, use the Response and Status properties of the exception to determine the response from the server.
Produs | Versiuni |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 2.0, 2.1 |
UWP | 10.0 |
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