HttpWebRequest.IfModifiedSince-Eigenschaft

Ruft den Wert des If-Modified-Since-HTTP-Headers ab oder legt diesen fest.

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

Syntax

'Declaration
Public Property IfModifiedSince As DateTime
'Usage
Dim instance As HttpWebRequest
Dim value As DateTime

value = instance.IfModifiedSince

instance.IfModifiedSince = value

public DateTime IfModifiedSince { get; set; }

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)

Eigenschaftenwert

Eine DateTime mit dem Inhalt des If-Modified-Since-HTTP-Headers. Der Standardwert ist das aktuelle Datum und die aktuelle Uhrzeit.

Hinweise

Es wird davon ausgegangen, dass der IfModifiedSince-Eigenschaft die Ortszeit zugrunde liegt.

Hinweis

Der Wert für diese Eigenschaft wird in der WebHeaderCollection gespeichert. Wenn WebHeaderCollection festgelegt wird, geht der Eigenschaftenwert verloren.

Beispiel

Im folgenden Codebeispiel wird die IfModifiedSince-Eigenschaft überprüft.

    ' Create a new 'Uri' object with the mentioned string.
    Dim myUri As New Uri("https://www.contoso.com")
    ' Create a new 'HttpWebRequest' object with the above 'Uri' object.
    Dim myHttpWebRequest As HttpWebRequest = CType(WebRequest.Create(myUri), HttpWebRequest)
    ' Create a new 'DateTime' object.
    Dim today As DateTime = DateTime.Now
    If DateTime.Compare(today, myHttpWebRequest.IfModifiedSince) = 0 Then
        ' Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
        Dim myHttpWebResponse As HttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
        Console.WriteLine("Response headers " + ControlChars.Cr + "{0}" + ControlChars.Cr, myHttpWebResponse.Headers)
        Dim streamResponse As Stream = myHttpWebResponse.GetResponseStream()
        Dim streamRead As New StreamReader(streamResponse)
        Dim readBuff(256) As [Char]
        Dim count As Integer = streamRead.Read(readBuff, 0, 256)
        Console.WriteLine(ControlChars.Cr + "The contents of Html Page are :  " + ControlChars.Cr)
        While count > 0
            Dim outputData As New [String](readBuff, 0, count)
            Console.Write(outputData)
            count = streamRead.Read(readBuff, 0, 256)
        End While
   ' Close the Stream object.
streamResponse.Close()
streamRead.Close()
   ' Release the HttpWebResponse Resource.
myHttpWebResponse.Close()
        Console.WriteLine(ControlChars.Cr + "Press 'Enter' key to continue.................")
        Console.Read()
    Else
        Console.WriteLine((ControlChars.Cr + "The page has been modified since " + today))
    End If

// Create a new 'Uri' object with the mentioned string.
Uri myUri =new Uri("https://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.Now;
if (DateTime.Compare(today,myHttpWebRequest.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.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);
}

      // Create a new 'Uri' object with the mentioned string.
      Uri^ myUri = gcnew Uri( "https://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("https://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);
}

Plattformen

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

.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.

Versionsinformationen

.NET Framework

Unterstützt in: 2.0, 1.1, 1.0

.NET Compact Framework

Unterstützt in: 2.0, 1.0

Siehe auch

Referenz

HttpWebRequest-Klasse
HttpWebRequest-Member
System.Net-Namespace