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FileWebRequest.BeginGetResponse Method

Begins an asynchronous request for a file system resource.

[Visual Basic]
Overrides Public Function BeginGetResponse( _
   ByVal callback As AsyncCallback, _
   ByVal state As Object _
) As IAsyncResult
[C#]
public override IAsyncResult BeginGetResponse(
 AsyncCallback callback,
 object state
);
[C++]
public: IAsyncResult* BeginGetResponse(
 AsyncCallback* callback,
 Object* state
);
[JScript]
public override function BeginGetResponse(
   callback : AsyncCallback,
 state : Object
) : IAsyncResult;

Parameters

callback
The AsyncCallback delegate.
state
An object containing state information for this request.

Return Value

An IAsyncResult that references the asynchronous request.

Exceptions

Exception Type Condition
InvalidOperationException The stream is already in use by a previous call to BeginGetResponse.

Remarks

The BeginGetResponse method starts an asynchronous request for a file system resource. The asynchronous callback method that implements the AsyncCallback delegate uses the EndGetResponse method to return the actual FileWebResponse.

Example

[Visual Basic, C#, C++] The following example uses the BeginGetResponse method to asynchronously a file system resource.

[Visual Basic] 
Public Class RequestDeclare
    Public myFileWebRequest As FileWebRequest
     
    Public Sub New()
        myFileWebRequest = Nothing
    End Sub ' New
End Class ' RequestDeclare



Class FileWebRequest_resbeginend
    
    Public Shared allDone As New ManualResetEvent(False)
    
    ' Entry point which delegates to C-style main Private Function.
    Public Overloads Shared Sub Main()
        Main(GetCommandLineArgs())
    End Sub
    
    Overloads Shared Sub Main(args() As String)
        
        If args.Length < 2 Then
            Console.WriteLine(ControlChars.Cr + "Please enter the file name as command line parameter:")
            Console.WriteLine("Usage:FileWebRequest_resbeginend " + ChrW(60) + "systemname" + ChrW(62) + "/" + ChrW(60) + "sharedfoldername" + ChrW(62) + "/" + ChrW(60) + "filename" + ChrW(62) + ControlChars.Cr + "Example:FileWebRequest_resbeginend shafeeque/shaf/hello.txt")
        
        Else
            Try

                ' Place a webrequest.
                Dim myWebRequest As WebRequest = WebRequest.Create(("file://" + args(1)))
                ' Create an instance of the 'RequestDeclare' and associating the 'myWebRequest' to it.        
                Dim myRequestDeclare As New RequestDeclare()
                myRequestDeclare.myFileWebRequest = CType(myWebRequest, FileWebRequest)
                
                ' Begin the Asynchronous request for getting file content using 'BeginGetResponse()' method.    
                 Dim asyncResult As IAsyncResult = CType(myRequestDeclare.myFileWebRequest.BeginGetResponse(AddressOf RespCallback, myRequestDeclare), IAsyncResult)
                 allDone.WaitOne()

            
            Catch e As ArgumentNullException
                Console.WriteLine(("ArgumentNullException is :" + e.Message))
            Catch e As UriFormatException
                Console.WriteLine(("UriFormatException is :" + e.Message))
            End Try
        End If
    End Sub ' Main
    
    
    Private Shared Sub RespCallback(ar As IAsyncResult)



        ' State of request is asynchronous.
        Dim requestDeclare As RequestDeclare = CType(ar.AsyncState, RequestDeclare)
        
        Dim myFileWebRequest As FileWebRequest = requestDeclare.myFileWebRequest
        
        ' End the Asynchronus request by calling the 'EndGetResponse()' method.
        Dim myFileWebResponse As FileWebResponse = CType(myFileWebRequest.EndGetResponse(ar), FileWebResponse)
        
        ' Reade the response into Stream.
        Dim streamReader As New StreamReader(myFileWebResponse.GetResponseStream())

       
        Dim readBuffer(256) As [Char]
        
        Dim count As Integer = streamReader.Read(readBuffer, 0, 256)
        
        Console.WriteLine("The contents of the file are :"+ControlChars.Cr)
        
        While count > 0
            Dim str As New [String](readBuffer, 0, count)
            Console.WriteLine(str)
            count = streamReader.Read(readBuffer, 0, 256)
        End While
         streamReader.Close()
        ' Release the response object resources.
         myFileWebResponse.Close()
        allDone.Set()
        Console.WriteLine("File reading is over.")
    End Sub ' RespCallback 
End Class ' FileWebRequest_resbeginend


[C#] 

    public class RequestDeclare
    {
       public FileWebRequest myFileWebRequest;    
       
         public RequestDeclare()
        {
            myFileWebRequest = null;
        }
    }
    
    
    class FileWebRequest_resbeginend
    {

        public static ManualResetEvent allDone = new ManualResetEvent(false);

        static void Main(string[] args)
        {
            
            if (args.Length < 1)
            {
               Console.WriteLine("\nPlease enter the file name as command line parameter:");
                Console.WriteLine("Usage:FileWebRequest_resbeginend <systemname>/<sharedfoldername>/<filename>\nExample:FileWebRequest_resbeginend shafeeque/shaf/hello.txt");
            }  
            else
            {
              try
            {


                  // Place a 'Webrequest'.
                  WebRequest myWebRequest= WebRequest.Create("file://"+args[0]);
                  // Create an instance of the 'RequestDeclare' and associating the 'myWebRequest' to it.        
                  RequestDeclare myRequestDeclare = new RequestDeclare();
                  myRequestDeclare.myFileWebRequest = (FileWebRequest)myWebRequest;
              

                  // Begin the Asynchronous request for getting file content using 'BeginGetResponse()' method.    
                  IAsyncResult asyncResult =(IAsyncResult) myRequestDeclare.myFileWebRequest.BeginGetResponse(new AsyncCallback(RespCallback),myRequestDeclare);            
                  allDone.WaitOne();

            
               }
            catch(ArgumentNullException e)
               {
                  Console.WriteLine("ArgumentNullException is :"+e.Message);
               }
               catch(UriFormatException e)
              {
                  Console.WriteLine("UriFormatException is :"+e.Message);
              }
           }
        }

      private static void RespCallback(IAsyncResult ar)
      {    


               // State of request is asynchronous.
                RequestDeclare requestDeclare=(RequestDeclare) ar.AsyncState;
                    
                FileWebRequest  myFileWebRequest=requestDeclare.myFileWebRequest;
            
               // End the Asynchronus request by calling the 'EndGetResponse()' method.
                
                FileWebResponse myFileWebResponse = (FileWebResponse) myFileWebRequest.EndGetResponse(ar);


                // Reade the response into Stream.
                StreamReader streamReader= new StreamReader(myFileWebResponse.GetResponseStream());


                Char[] readBuffer = new Char[256];
                    
                int count = streamReader.Read( readBuffer, 0, 256 );

                Console.WriteLine("The contents of the file are :\n");
        
                while (count > 0) 
                {
                    String str = new String(readBuffer, 0, count);
                    Console.WriteLine(str);
                    count = streamReader.Read(readBuffer, 0, 256);
                }
                
                streamReader.Close();
                // Release the response object resources.
                myFileWebResponse.Close();
                allDone.Set();
                Console.WriteLine("File reading is over.");    
        }

    }

[C++] 
public __gc class RequestDeclare {
public:
   FileWebRequest*  myFileWebRequest;

   RequestDeclare() {
      myFileWebRequest = 0;
   }
};

__gc class FileWebRequest_resbeginend {
public:
   static ManualResetEvent* allDone = new ManualResetEvent(false);

   static void RespCallback(IAsyncResult* ar) {
      // State of request is asynchronous.
      RequestDeclare* requestDeclare = dynamic_cast<RequestDeclare*>(ar->AsyncState);

      FileWebRequest*  myFileWebRequest=requestDeclare->myFileWebRequest;

      // End the Asynchronus request by calling the 'EndGetResponse()' method.
      FileWebResponse* myFileWebResponse = dynamic_cast<FileWebResponse*> (myFileWebRequest->EndGetResponse(ar));

      // Reade the response into Stream.
      StreamReader* streamReader = new StreamReader(myFileWebResponse->GetResponseStream());

      Char readBuffer[] = new Char[256];
      int count = streamReader->Read(readBuffer, 0, 256);
      Console::WriteLine(S"The contents of the file are :\n");

      while (count > 0) {
         String* str = new String(readBuffer, 0, count);
         Console::WriteLine(str);
         count = streamReader->Read(readBuffer, 0, 256);
      }

      streamReader->Close();
      // Release the response Object* resources.
      myFileWebResponse->Close();
      allDone->Set();
      Console::WriteLine(S"File reading is over.");
   }
};

int main() {
   String* args[] = Environment::GetCommandLineArgs();
   if (args->Length < 2) {
      Console::WriteLine(S"\nPlease enter the file name as command line parameter:");
      Console::WriteLine(S"Usage:FileWebRequest_resbeginend <systemname>/<sharedfoldername>/<filename>\n");
      Console::WriteLine(S"Example:FileWebRequest_resbeginend shafeeque/shaf/hello.txt");
   } else {
      try {
         // Place a 'Webrequest'.
         WebRequest* myWebRequest= WebRequest::Create(String::Concat(S"file://", args[1]));
         // Create an instance of the 'RequestDeclare' and associating the 'myWebRequest' to it.
         RequestDeclare* myRequestDeclare = new RequestDeclare();
         myRequestDeclare->myFileWebRequest = dynamic_cast<FileWebRequest*>(myWebRequest);

         // Begin the Asynchronous request for getting file content using 'BeginGetResponse()' method.
         IAsyncResult* asyncResult = dynamic_cast<IAsyncResult*>
            (myRequestDeclare->myFileWebRequest->BeginGetResponse(new AsyncCallback(0, 
            &FileWebRequest_resbeginend::RespCallback), myRequestDeclare));
         FileWebRequest_resbeginend::allDone->WaitOne();
      } catch (ArgumentNullException* e) {
         Console::WriteLine(S"ArgumentNullException is : {0}", e->Message);
      } catch (UriFormatException* e) {
         Console::WriteLine(S"UriFormatException is : {0}", e->Message);
      }
   }
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

FileWebRequest Class | FileWebRequest Members | System.Net Namespace | GetResponse | EndGetResponse | Making Asynchronous Requests

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