HttpWebRequest.BeginGetResponse(AsyncCallback, Object) Metodo
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Avvia una richiesta asincrona a una risorsa Internet.
public:
override IAsyncResult ^ BeginGetResponse(AsyncCallback ^ callback, System::Object ^ state);public override IAsyncResult BeginGetResponse (AsyncCallback callback, object state);public override IAsyncResult BeginGetResponse (AsyncCallback? callback, object? state);override this.BeginGetResponse : AsyncCallback * obj -> IAsyncResultPublic Overrides Function BeginGetResponse (callback As AsyncCallback, state As Object) As IAsyncResultParametri
- callback
- AsyncCallback
Delegato AsyncCallback.
- state
- Object
Oggetto stato per questa richiesta.
Restituisce
IAsyncResult che fa riferimento alla richiesta asincrona per una risposta.
Eccezioni
Il flusso è già in uso da una chiamata precedente a BeginGetResponse(AsyncCallback, Object)
-o-
TransferEncoding è impostato su un valore e SendChunked è false.
-o-
Il pool di thread sta esaurendo i thread.
Method è GET o HEAD e ContentLength è maggiore di zero o SendChunked è true.
-o-
KeepAlive è true, AllowWriteStreamBuffering è falsee ContentLength è -1, SendChunked è false e Method è POST o PUT.
-o-
Il HttpWebRequest ha un corpo dell'entità, ma il metodo BeginGetResponse(AsyncCallback, Object) viene chiamato senza chiamare il metodo BeginGetRequestStream(AsyncCallback, Object).
-o-
Il ContentLength è maggiore di zero, ma l'applicazione non scrive tutti i dati promessi.
Abort() è stato chiamato in precedenza.
Esempio
Nell'esempio di codice seguente viene utilizzato il metodo BeginGetResponse per effettuare una richiesta asincrona per una risorsa Internet.
Nota
Nel caso di richieste asincrone, è responsabilità dell'applicazione client implementare il proprio meccanismo di timeout. Nell'esempio di codice seguente viene illustrato come eseguire questa operazione.
#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.
const int BUFFER_SIZE;
public:
StringBuilder^ requestData;
array<Byte>^BufferRead;
HttpWebRequest^ request;
HttpWebResponse^ response;
Stream^ streamResponse;
RequestState()
: BUFFER_SIZE( 1024 )
{
BufferRead = gcnew array<Byte>(BUFFER_SIZE);
requestData = gcnew StringBuilder( "" );
request = nullptr;
streamResponse = nullptr;
}
};
ref class HttpWebRequest_BeginGetResponse
{
public:
static ManualResetEvent^ allDone = gcnew ManualResetEvent( false );
literal int BUFFER_SIZE = 1024;
literal int DefaultTimeOut = 120000; // 2 minute timeout
// Abort the request if the timer fires.
static void TimeoutCallback( Object^ state, bool timedOut )
{
if ( timedOut )
{
HttpWebRequest^ request = dynamic_cast<HttpWebRequest^>(state);
if ( request != nullptr )
{
request->Abort();
}
}
}
static void RespCallback( IAsyncResult^ asynchronousResult )
{
try
{
// State of request is asynchronous.
RequestState^ myRequestState = dynamic_cast<RequestState^>(asynchronousResult->AsyncState);
HttpWebRequest^ myHttpWebRequest = myRequestState->request;
myRequestState->response = dynamic_cast<HttpWebResponse^>(myHttpWebRequest->EndGetResponse( asynchronousResult ));
// Read the response into a Stream object.
Stream^ responseStream = myRequestState->response->GetResponseStream();
myRequestState->streamResponse = responseStream;
// Begin the Reading of the contents of the HTML page and print it to the console.
IAsyncResult^ asynchronousInputRead = responseStream->BeginRead( myRequestState->BufferRead, 0, BUFFER_SIZE, gcnew AsyncCallback( ReadCallBack ), myRequestState );
return;
}
catch ( WebException^ e )
{
Console::WriteLine( "\nRespCallback Exception raised!" );
Console::WriteLine( "\nMessage: {0}", e->Message );
Console::WriteLine( "\nStatus: {0}", e->Status );
}
allDone->Set();
}
static void ReadCallBack( IAsyncResult^ asyncResult )
{
try
{
RequestState^ myRequestState = dynamic_cast<RequestState^>(asyncResult->AsyncState);
Stream^ responseStream = myRequestState->streamResponse;
int read = responseStream->EndRead( asyncResult );
// Read the HTML page and then print it 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 );
return;
}
else
{
Console::WriteLine( "\nThe contents of the Html page are : " );
if ( myRequestState->requestData->Length > 1 )
{
String^ stringContent;
stringContent = myRequestState->requestData->ToString();
Console::WriteLine( stringContent );
}
Console::WriteLine( "Press any key to continue.........." );
Console::ReadLine();
responseStream->Close();
}
}
catch ( WebException^ e )
{
Console::WriteLine( "\nReadCallBack Exception raised!" );
Console::WriteLine( "\nMessage: {0}", e->Message );
Console::WriteLine( "\nStatus: {0}", e->Status );
}
allDone->Set();
}
};
int main()
{
try
{
// Create a HttpWebrequest object to the desired URL.
HttpWebRequest^ myHttpWebRequest = dynamic_cast<HttpWebRequest^>(WebRequest::Create( "http://www.contoso.com" ));
/**
* If you are behind a firewall and you do not have your browser proxy setup
* you need to use the following proxy creation code.
// Create a proxy object.
WebProxy* myProxy = new WebProxy();
// Associate a new Uri object to the _wProxy object, using the proxy address
// selected by the user.
myProxy.Address = new Uri(S"http://myproxy");
// Finally, initialize the Web request object proxy property with the _wProxy
// object.
myHttpWebRequest.Proxy=myProxy;
***/
// Create an instance of the RequestState and assign the previous myHttpWebRequest
// object to its request field.
RequestState^ myRequestState = gcnew RequestState;
myRequestState->request = myHttpWebRequest;
// Start the asynchronous request.
IAsyncResult^ result = dynamic_cast<IAsyncResult^>(myHttpWebRequest->BeginGetResponse( gcnew AsyncCallback( HttpWebRequest_BeginGetResponse::RespCallback ), myRequestState ));
// this line impliments the timeout, if there is a timeout, the callback fires and the request becomes aborted
ThreadPool::RegisterWaitForSingleObject( result->AsyncWaitHandle, gcnew WaitOrTimerCallback( HttpWebRequest_BeginGetResponse::TimeoutCallback ), myHttpWebRequest, HttpWebRequest_BeginGetResponse::DefaultTimeOut, true );
// The response came in the allowed time. The work processing will happen in the
// callback function.
HttpWebRequest_BeginGetResponse::allDone->WaitOne();
// Release the HttpWebResponse resource.
myRequestState->response->Close();
}
catch ( WebException^ e )
{
Console::WriteLine( "\nMain Exception raised!" );
Console::WriteLine( "\nMessage: {0}", e->Message );
Console::WriteLine( "\nStatus: {0}", e->Status );
Console::WriteLine( "Press any key to continue.........." );
}
catch ( Exception^ e )
{
Console::WriteLine( "\nMain Exception raised!" );
Console::WriteLine( "Source : {0} ", e->Source );
Console::WriteLine( "Message : {0} ", e->Message );
Console::WriteLine( "Press any key to continue.........." );
Console::Read();
}
}
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 HttpWebRequest request;
public HttpWebResponse response;
public Stream streamResponse;
public RequestState()
{
BufferRead = new byte[BUFFER_SIZE];
requestData = new StringBuilder("");
request = null;
streamResponse = null;
}
}
class HttpWebRequest_BeginGetResponse
{
public static ManualResetEvent allDone= new ManualResetEvent(false);
const int BUFFER_SIZE = 1024;
const int DefaultTimeout = 2 * 60 * 1000; // 2 minutes timeout
// Abort the request if the timer fires.
private static void TimeoutCallback(object state, bool timedOut) {
if (timedOut) {
HttpWebRequest request = state as HttpWebRequest;
if (request != null) {
request.Abort();
}
}
}
static void Main()
{
try
{
// Create a HttpWebrequest object to the desired URL.
HttpWebRequest myHttpWebRequest= (HttpWebRequest)WebRequest.Create("http://www.contoso.com");
/**
* If you are behind a firewall and you do not have your browser proxy setup
* you need to use the following proxy creation code.
// Create a proxy object.
WebProxy myProxy = new WebProxy();
// Associate a new Uri object to the _wProxy object, using the proxy address
// selected by the user.
myProxy.Address = new Uri("http://myproxy");
// Finally, initialize the Web request object proxy property with the _wProxy
// object.
myHttpWebRequest.Proxy=myProxy;
***/
// Create an instance of the RequestState and assign the previous myHttpWebRequest
// object to its request field.
RequestState myRequestState = new RequestState();
myRequestState.request = myHttpWebRequest;
// Start the asynchronous request.
IAsyncResult result=
(IAsyncResult) myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestState);
// this line implements the timeout, if there is a timeout, the callback fires and the request becomes aborted
ThreadPool.RegisterWaitForSingleObject (result.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), myHttpWebRequest, DefaultTimeout, true);
// The response came in the allowed time. The work processing will happen in the
// callback function.
allDone.WaitOne();
// Release the HttpWebResponse resource.
myRequestState.response.Close();
}
catch(WebException e)
{
Console.WriteLine("\nMain Exception raised!");
Console.WriteLine("\nMessage:{0}",e.Message);
Console.WriteLine("\nStatus:{0}",e.Status);
Console.WriteLine("Press any key to continue..........");
}
catch(Exception e)
{
Console.WriteLine("\nMain Exception raised!");
Console.WriteLine("Source :{0} " , e.Source);
Console.WriteLine("Message :{0} " , e.Message);
Console.WriteLine("Press any key to continue..........");
Console.Read();
}
}
private static void RespCallback(IAsyncResult asynchronousResult)
{
try
{
// State of request is asynchronous.
RequestState myRequestState=(RequestState) asynchronousResult.AsyncState;
HttpWebRequest myHttpWebRequest=myRequestState.request;
myRequestState.response = (HttpWebResponse) myHttpWebRequest.EndGetResponse(asynchronousResult);
// Read the response into a Stream object.
Stream responseStream = myRequestState.response.GetResponseStream();
myRequestState.streamResponse=responseStream;
// Begin the Reading of the contents of the HTML page and print it to the console.
IAsyncResult asynchronousInputRead = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
return;
}
catch(WebException e)
{
Console.WriteLine("\nRespCallback Exception raised!");
Console.WriteLine("\nMessage:{0}",e.Message);
Console.WriteLine("\nStatus:{0}",e.Status);
}
allDone.Set();
}
private static void ReadCallBack(IAsyncResult asyncResult)
{
try
{
RequestState myRequestState = (RequestState)asyncResult.AsyncState;
Stream responseStream = myRequestState.streamResponse;
int read = responseStream.EndRead( asyncResult );
// Read the HTML page and then print it 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);
return;
}
else
{
Console.WriteLine("\nThe contents of the Html page are : ");
if(myRequestState.requestData.Length>1)
{
string stringContent;
stringContent = myRequestState.requestData.ToString();
Console.WriteLine(stringContent);
}
Console.WriteLine("Press any key to continue..........");
Console.ReadLine();
responseStream.Close();
}
}
catch(WebException e)
{
Console.WriteLine("\nReadCallBack Exception raised!");
Console.WriteLine("\nMessage:{0}",e.Message);
Console.WriteLine("\nStatus:{0}",e.Status);
}
allDone.Set();
}
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
Public Class RequestState
' This class stores the State of the request.
Private BUFFER_SIZE As Integer = 1024
Public requestData As StringBuilder
Public BufferRead() As Byte
Public request As HttpWebRequest
Public response As HttpWebResponse
Public streamResponse As Stream
Public Sub New()
BufferRead = New Byte(BUFFER_SIZE) {}
requestData = New StringBuilder("")
request = Nothing
streamResponse = Nothing
End Sub
End Class
Class HttpWebRequest_BeginGetResponse
Public Shared allDone As New ManualResetEvent(False)
Private BUFFER_SIZE As Integer = 1024
Private DefaultTimeout As Integer = 2 * 60 * 1000
' 2 minutes timeout
' Abort the request if the timer fires.
Private Shared Sub TimeoutCallback(state As Object, timedOut As Boolean)
If timedOut Then
Dim request As HttpWebRequest = state
If Not (request Is Nothing) Then
request.Abort()
End If
End If
End Sub
Shared Sub Main()
Try
' Create a HttpWebrequest object to the desired URL.
Dim myHttpWebRequest As HttpWebRequest = WebRequest.Create("http://www.contoso.com")
' Create an instance of the RequestState and assign the previous myHttpWebRequest
' object to its request field.
Dim myRequestState As New RequestState()
myRequestState.request = myHttpWebRequest
Dim myResponse As New HttpWebRequest_BeginGetResponse()
' Start the asynchronous request.
Dim result As IAsyncResult = CType(myHttpWebRequest.BeginGetResponse(New AsyncCallback(AddressOf RespCallback), myRequestState), IAsyncResult)
' this line implements the timeout, if there is a timeout, the callback fires and the request aborts.
ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, New WaitOrTimerCallback(AddressOf TimeoutCallback), myHttpWebRequest, myResponse.DefaultTimeout, True)
' The response came in the allowed time. The work processing will happen in the
' callback function.
allDone.WaitOne()
' Release the HttpWebResponse resource.
myRequestState.response.Close()
Catch e As WebException
Console.WriteLine(ControlChars.Lf + "Main Exception raised!")
Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
Console.WriteLine("Press any key to continue..........")
Catch e As Exception
Console.WriteLine(ControlChars.Lf + "Main Exception raised!")
Console.WriteLine("Source :{0} ", e.Source)
Console.WriteLine("Message :{0} ", e.Message)
Console.WriteLine("Press any key to continue..........")
Console.Read()
End Try
End Sub
Private Shared Sub RespCallback(asynchronousResult As IAsyncResult)
Try
' State of request is asynchronous.
Dim myRequestState As RequestState = CType(asynchronousResult.AsyncState, RequestState)
Dim myHttpWebRequest As HttpWebRequest = myRequestState.request
myRequestState.response = CType(myHttpWebRequest.EndGetResponse(asynchronousResult), HttpWebResponse)
' Read the response into a Stream object.
Dim responseStream As Stream = myRequestState.response.GetResponseStream()
myRequestState.streamResponse = responseStream
' Begin the Reading of the contents of the HTML page and print it to the console.
Dim asynchronousInputRead As IAsyncResult = responseStream.BeginRead(myRequestState.BufferRead, 0, 1024, New AsyncCallback(AddressOf ReadCallBack), myRequestState)
Return
Catch e As WebException
Console.WriteLine(ControlChars.Lf + "RespCallback Exception raised!")
Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
End Try
allDone.Set()
End Sub
Private Shared Sub ReadCallBack(asyncResult As IAsyncResult)
Try
Dim myRequestState As RequestState = CType(asyncResult.AsyncState, RequestState)
Dim responseStream As Stream = myRequestState.streamResponse
Dim read As Integer = responseStream.EndRead(asyncResult)
' Read the HTML page and then print it 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, 1024, New AsyncCallback(AddressOf ReadCallBack), myRequestState)
Return
Else
Console.WriteLine(ControlChars.Lf + "The contents of the Html page are : ")
If myRequestState.requestData.Length > 1 Then
Dim stringContent As String
stringContent = myRequestState.requestData.ToString()
Console.WriteLine(stringContent)
End If
Console.WriteLine("Press any key to continue..........")
Console.ReadLine()
responseStream.Close()
End If
Catch e As WebException
Console.WriteLine(ControlChars.Lf + "ReadCallBack Exception raised!")
Console.WriteLine(ControlChars.Lf + "Message:{0}", e.Message)
Console.WriteLine(ControlChars.Lf + "Status:{0}", e.Status)
End Try
allDone.Set()
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 dalla risorsa Internet. Il metodo di callback asincrono usa il metodo EndGetResponse per restituire il WebResponseeffettivo .
Un ProtocolViolationException viene generato in diversi casi quando le proprietà impostate nella classe HttpWebRequest sono in conflitto. Questa eccezione si verifica se un'applicazione imposta la proprietà ContentLength e la proprietà SendChunked su truee quindi invia una richiesta HTTP GET. Questa eccezione si verifica se un'applicazione tenta di inviare blocchi a un server che supporta solo il protocollo HTTP 1.0, in cui non è supportato. Questa eccezione si verifica se un'applicazione tenta di inviare dati senza impostare la proprietà ContentLength o il SendChunked viene false quando il buffering è disabilitato e in una connessione keepalive (la proprietà KeepAlive è true).
Se viene generata una WebException, utilizzare le proprietà Response e Status dell'eccezione per determinare la risposta dal server.
Il metodo BeginGetResponse richiede il completamento di alcune attività di configurazione sincrone (risoluzione DNS, rilevamento proxy e connessione socket TCP, ad esempio) prima che questo metodo diventi asincrono. Di conseguenza, questo metodo non deve mai essere chiamato su un thread dell'interfaccia utente perché potrebbe richiedere molto tempo (fino a diversi minuti a seconda delle impostazioni di rete) per completare le attività di installazione sincrone iniziali prima che venga generata un'eccezione per un errore o il metodo abbia esito positivo.
Per altre informazioni sul pool di thread, vedere Pool di thread gestiti.
Nota
L'applicazione non può combinare metodi sincroni e asincroni per una determinata richiesta. Se si chiama il metodo BeginGetRequestStream, è necessario usare il metodo BeginGetResponse per recuperare la risposta.
Nota
Questo membro restituisce informazioni di traccia quando si abilita la traccia di rete nell'applicazione. Per altre informazioni, vedere Traccia di rete in .NET Framework.
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