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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 DateTime IfModifiedSince { get; set; }

Property Value

Type: System.DateTime
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 =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.
Uri* myUri = new Uri(S"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(S"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(S"\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(S"\nPress 'Enter' key to continue.................");
   Console::Read();
} else {
   Console::WriteLine(S"\nThe page has been modified since {0}", __box( today));
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

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