HttpWebRequest.BeginGetResponse(AsyncCallback, Object) 方法

參考

定義

命名空間:: System.Net

組件:: System.Net.Requests.dll

組件:: System.dll

組件:: netstandard.dll

來源:: HttpWebRequest.cs

來源:: HttpWebRequest.cs

來源:: HttpWebRequest.cs

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

開始對因特網資源的異步要求。

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 -> IAsyncResult

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

參數

callback: AsyncCallback

AsyncCallback 委派。

state: Object

這個要求的狀態物件。

傳回

IAsyncResult

參考回應異步要求的 IAsyncResult。

例外狀況

InvalidOperationException

先前對 BeginGetResponse(AsyncCallback, Object) 的呼叫已使用數據流

-或-

TransferEncoding 設定為值，且 SendChunkedfalse。

-或-

線程集區已用盡線程。

ProtocolViolationException

Method 為 GET 或 HEAD，且 ContentLength 大於零或 SendChunked 為 true。

-或-

KeepAlive 是 true，AllowWriteStreamBuffering 是 false，ContentLength 為 -1，SendChunked 是 false，Method 為 POST 或 PUT。

-或-

HttpWebRequest 具有實體主體，但呼叫 BeginGetResponse(AsyncCallback, Object) 方法而不呼叫 BeginGetRequestStream(AsyncCallback, Object) 方法。

-或-

ContentLength 大於零，但應用程式不會寫入所有承諾的數據。

WebException

先前呼叫 Abort()。

範例

下列程式代碼範例會使用 BeginGetResponse 方法來對因特網資源提出異步要求。

注意

在異步要求的情況下，用戶端應用程式必須負責實作自己的逾時機制。下列程式代碼範例示範如何執行。

#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

備註

謹慎

WebRequest、HttpWebRequest、ServicePoint和 WebClient 已經過時，您不應該將它們用於新的開發。請改用 HttpClient。

BeginGetResponse 方法會啟動來自因特網資源的回應異步要求。異步回呼方法會使用 EndGetResponse 方法來傳回實際的 WebResponse。

當 HttpWebRequest 類別上設定的屬性發生衝突時，會在數種情況下擲回 ProtocolViolationException。如果應用程式將 ContentLength 屬性和 SendChunked 屬性設定為 true，然後傳送 HTTP GET 要求，就會發生這個例外狀況。如果應用程式嘗試將區塊傳送至只支援 HTTP 1.0 通訊協定的伺服器，但不支援此通訊協定，就會發生此例外狀況。如果應用程式嘗試在不設定 ContentLength 屬性的情況下傳送數據，或在停用緩衝處理時 falseSendChunked，且在保留連線上發生此例外狀況（KeepAlive 屬性為 true）.

如果擲回 WebException，請使用例外狀況的 Response 和 Status 屬性來判斷伺服器的回應。

BeginGetResponse 方法需要一些同步設定工作才能完成（例如 DNS 解析、Proxy 偵測和 TCP 套接字連線），然後這個方法才會變成異步。因此，這個方法不應該在使用者介面（UI）線程上呼叫，因為可能需要相當長的時間（視網路設定而定，最多幾分鐘的時間），才能完成初始同步設定工作，然後再擲回錯誤的例外狀況或方法成功。

若要深入瞭解線程集區，請參閱受控線程集區。

注意

您的應用程式無法混合特定要求的同步和異步方法。如果您呼叫 BeginGetRequestStream 方法，則必須使用 BeginGetResponse 方法來擷取回應。

注意

當您在應用程式中啟用網路追蹤時，此成員會輸出追蹤資訊。如需詳細資訊，請參閱 .NET Framework中的網路追蹤。

適用於

另請參閱

DefaultProxy 元素（網路設定）

共用方式為

HttpWebRequest.BeginGetResponse(AsyncCallback, Object) 方法

定義

參數

傳回

例外狀況

範例

備註

適用於

另請參閱

意見反應

其他資源