HttpWebRequest.IfModifiedSince Özellik

Tanım

Ad Alanı:

System.Net

Bütünleştirilmiş Kod:

System.Net.Requests.dll

Kaynak:

HttpWebRequest.cs

If-Modified-Since HTTP üst bilgisinin değerini alır veya ayarlar.

public:
 property DateTime IfModifiedSince { DateTime get(); void set(DateTime value); };

public DateTime IfModifiedSince { get; set; }

member this.IfModifiedSince : DateTime with get, set

Public Property IfModifiedSince As DateTime

Özellik Değeri

DateTime

If-Modified-Since HTTP üst bilgisinin içeriğini içeren bir DateTime.

Örnekler

Aşağıdaki kod örneği IfModifiedSince özelliğini denetler.

// 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 targetDate = DateTime::Now;
// Set a target date of a week ago
targetDate.AddDays(-7.0);
myHttpWebRequest->IfModifiedSince = targetDate;

try
{
     
  // 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();
}
catch ( WebException^ e )
{
  if (e->Response)
  {
    if ( ((HttpWebResponse ^)e->Response)->StatusCode == HttpStatusCode::NotModified)
      Console::WriteLine("\nThe page has not been modified since {0}", targetDate);
    else
      Console::WriteLine("\nUnexpected status code = {0}", ((HttpWebResponse ^)e->Response)->StatusCode);  
  }
  else
    Console::WriteLine("\nUnexpected Web Exception {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 targetDate = DateTime.Now;
// Set a target date of a week ago
targetDate.AddDays(-7.0);
myHttpWebRequest.IfModifiedSince = targetDate;

try
{
  // Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
  HttpWebResponse myHttpWebResponse=(HttpWebResponse)myHttpWebRequest.GetResponse();
  Console.WriteLine("Response headers for recently modified page\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();
}
catch(WebException e)
{
  if (e.Response != null)
  {
    if ( ((HttpWebResponse)e.Response).StatusCode == HttpStatusCode.NotModified)
      Console.WriteLine("\nThe page has not been modified since "+targetDate);
    else
      Console.WriteLine("\nUnexpected status code = " + ((HttpWebResponse)e.Response).StatusCode);
  }
  else
            {
                Console.WriteLine("\nUnexpected Web Exception " + e.Message);
            }
        }

' Create a new 'Uri' object with the mentioned string.
Dim myUri As New Uri("http://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 targetDate As DateTime = DateTime.Now
targetDate.AddDays(-7.0)
myHttpWebRequest.IfModifiedSince = targetDate

Try
  ' Assign the response object of 'HttpWebRequest' to a 'HttpWebResponse' variable.
  Dim myHttpWebResponse As HttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
  Console.WriteLine("Response headers for recently modified page" + 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()
Catch e As WebException
  If e.Response IsNot Nothing
  
    If CType(e.Response,HttpWebResponse).StatusCode = HttpStatusCode.NotModified
      Console.WriteLine((ControlChars.Cr + "The page has not been modified since " + targetDate))
    Else
      Console.WriteLine(ControlChars.Cr + "Unexpected status code = " + Ctype(e.Response,HttpWebResponse).StatusCode)
    End If
  Else
    Console.WriteLine(ControlChars.Cr + "Unexpected Web Exception " + e.Message) 
  End If
End Try

Açıklamalar

Dikkat

WebRequest, HttpWebRequest, ServicePointve WebClient kullanım dışıdır ve bunları yeni geliştirme için kullanmamalısınız. Bunun yerine HttpClient kullanın.

If-Modified-Since üst bilgisi nullise, dönüş değeri DateTime.MinValueolarak ayarlanır.

IfModifiedSince özelliği standart bir System.DateTime nesnesidir ve DateTimeKind.Local, DateTimeKind.Utcveya DateTimeKind.UnspecifiedSystem.DateTimeKind bir alanı içerebilir. IfModifiedSince özelliği kullanılırken herhangi bir zaman ayarlanabilir. DateTimeKind.Unspecified ayarlanır veya alınırsa, IfModifiedSince özelliğinin DateTimeKind.Local (yerel saat) olduğu varsayılır.

System.Net ad alanında sınıflar, GMT (Utc) biçimini kullanarak standart biçimde iletim sırasında kablodaki IfModifiedSince özelliğini her zaman yazar.

IfModifiedSince özelliği DateTime.MinValueolarak ayarlanırsa, If-Modified-Since HTTP üst bilgisi Headers özelliğinden ve WebHeaderCollectionkaldırılır.

IfModifiedSince özelliği DateTime.MinValueise, If-Modified-Since HTTP üst bilgisinin Headers özelliğine ve WebHeaderCollectiondahil olmadığını gösterir.

Not

Bu özelliğin değeri WebHeaderCollectioniçinde depolanır. WebHeaderCollection ayarlanırsa özellik değeri kaybolur.

IfModifiedSince özelliği ayarlanırsa ve 304 (Değiştirilmedi) durum kodu döndürülürse, BeginGetResponse, GetResponseve EndGetResponse yöntemleri tarafından bir System.Net.WebException oluşturulur.