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HttpWebRequest.IfModifiedSince Property

Gets or sets the value of the If-Modified-Since HTTP header.

Namespace: System.Net
Assembly: System (in system.dll)

public:
property DateTime IfModifiedSince {
	DateTime get ();
	void set (DateTime value);
}
/** @property */
public DateTime get_IfModifiedSince ()

/** @property */
public void set_IfModifiedSince (DateTime value)

public function get IfModifiedSince () : DateTime

public function set IfModifiedSince (value : DateTime)

Not applicable.

Property Value

A DateTime that contains the contents of the If-Modified-Since HTTP header. The default value is the current date and time.

The IfModifiedSince property is assumed to be local time.

NoteNote:

The value for this property is stored in WebHeaderCollection. If WebHeaderCollection is set, the property value is lost.

The following code example checks the IfModifiedSince property.

      // Create a new 'Uri' object with the mentioned string.
      Uri^ myUri = gcnew Uri( "http://www.contoso.com" );
      
      // Create a new 'HttpWebRequest' object with the above 'Uri' object.
      HttpWebRequest^ myHttpWebRequest = dynamic_cast<HttpWebRequest^>(WebRequest::Create( myUri ));
      
      // Create a new 'DateTime' object.
      DateTime today = DateTime::Now;
      if ( DateTime::Compare( today, myHttpWebRequest->IfModifiedSince ) == 0 )
      {
         
         // Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
         HttpWebResponse^ myHttpWebResponse = dynamic_cast<HttpWebResponse^>(myHttpWebRequest->GetResponse());
         Console::WriteLine( "Response headers \n {0}\n", myHttpWebResponse->Headers );
         Stream^ streamResponse = myHttpWebResponse->GetResponseStream();
         StreamReader^ streamRead = gcnew StreamReader( streamResponse );
         array<Char>^readBuff = gcnew array<Char>(256);
         int count = streamRead->Read( readBuff, 0, 256 );
         Console::WriteLine( "\nThe contents of Html Page are :  \n" );
         while ( count > 0 )
         {
            String^ outputData = gcnew String( readBuff,0,count );
            Console::Write( outputData );
            count = streamRead->Read( readBuff, 0, 256 );
         }
         streamResponse->Close();
         streamRead->Close();
         
         // Release the HttpWebResponse Resource.
         myHttpWebResponse->Close();
         Console::WriteLine( "\nPress 'Enter' key to continue................." );
         Console::Read();
      }
      else
      {
         Console::WriteLine( "\nThe page has been modified since {0}", today );
      }
   }
   catch ( WebException^ e ) 
   {
      Console::WriteLine( "\nWebException Caught!" );
      Console::WriteLine( "Source  : {0}", e->Source );
      Console::WriteLine( "Message : {0}", e->Message );
   }
   catch ( Exception^ e ) 
   {
      Console::WriteLine( "\nException raised!" );
      Console::WriteLine( "Source  : {0}", e->Source );
      Console::WriteLine( "Message : {0}", e->Message );
   }

}


// Create a new 'Uri' object with the mentioned string.
Uri myUri = new Uri("http://www.contoso.com");

//Create a new 'HttpWebRequest' object with the above 'Uri' object.
HttpWebRequest myHttpWebRequest = (HttpWebRequest)
    (WebRequest.Create(myUri));
// Create a new 'DateTime' object.
DateTime today = DateTime.get_Now();

if (DateTime.Compare(today, 
    myHttpWebRequest.get_IfModifiedSince()) == 0) {
    // Assign the response object of 'HttpWebRequest' to a 
    //    'HttpWebResponse' variable.
    HttpWebResponse myHttpWebResponse = (HttpWebResponse)
        (myHttpWebRequest.GetResponse());
    Console.WriteLine("Response headers \n{0}\n", 
        myHttpWebResponse.get_Headers());
    Stream streamResponse = myHttpWebResponse.GetResponseStream();
    StreamReader streamRead = new StreamReader(streamResponse);
    char readBuff[] = new char[256];
    int count = streamRead.Read(readBuff, 0, 256);
    Console.WriteLine("\nThe contents of Html Page are :  \n");
    while (count > 0) {
        String outputData = new String(readBuff, 0, count);
        Console.Write(outputData);
        count = streamRead.Read(readBuff, 0, 256);
    }
    // Close the Stream object.
    streamResponse.Close();
    streamRead.Close();
    // Release the HttpWebResponse Resource.
    myHttpWebResponse.Close();
    Console.WriteLine("\nPress 'Enter' key to continue"
        + ".................");
    Console.Read();
}
else {
    Console.WriteLine("\nThe page has been modified since "
        + today);
}

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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