WebRequest.BeginGetResponse(AsyncCallback, Object) Metodo

Definizione

Spazio dei nomi:

System.Net

Assembly:

netstandard.dll, System.Net.Requests.dll

Origine:

WebRequest.cs

Quando sottoposto a override in una classe discendente, avvia una richiesta asincrona per una risorsa Internet.

public:
 virtual IAsyncResult ^ BeginGetResponse(AsyncCallback ^ callback, System::Object ^ state);

public virtual IAsyncResult BeginGetResponse(AsyncCallback? callback, object? state);

abstract member BeginGetResponse : AsyncCallback * obj -> IAsyncResult
override this.BeginGetResponse : AsyncCallback * obj -> IAsyncResult

Public Overridable Function BeginGetResponse (callback As AsyncCallback, state As Object) As IAsyncResult

Parametri

callback

AsyncCallback

Delegato AsyncCallback.

state

Object

Oggetto contenente informazioni sullo stato per questa richiesta asincrona.

Restituisce

IAsyncResult

IAsyncResult che fa riferimento alla richiesta asincrona.

Eccezioni

NotImplementedException

Qualsiasi tentativo viene effettuato per accedere al metodo, quando il metodo non viene sottoposto a override in una classe discendente.

Esempio

L'esempio seguente usa BeginGetResponse per richiedere in modo asincrono la risorsa di destinazione. Dopo aver ottenuto la risorsa, verrà eseguito il metodo di callback specificato.

#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

Commenti

Cautela

WebRequest, HttpWebRequest, ServicePointe WebClient sono obsoleti e non è consigliabile usarli per nuovi sviluppi. Usare invece HttpClient.

Il metodo BeginGetResponse avvia una richiesta asincrona per una risposta. Il metodo di callback che implementa il delegato AsyncCallback utilizza il metodo EndGetResponse per restituire il WebResponse dalla risorsa Internet.

Nota

La classe WebRequest è una classe abstract. Il comportamento effettivo delle istanze di WebRequest in fase di esecuzione è determinato dalla classe discendente restituita dal metodo WebRequest.Create. Per altre informazioni sui valori predefiniti e sulle eccezioni, vedere la documentazione per le classi discendenti, ad esempio HttpWebRequest e FileWebRequest.

Nota

Se viene generata un'eccezione WebException, utilizzare le proprietà Response e Status dell'eccezione per determinare la risposta dal server.

Vedi anche

• EndGetResponse(IAsyncResult)
• GetResponse()
• effettuare richieste asincrone