HttpWebRequest.IfModifiedSince Properti

Definisi

Ruang nama:

System.Net

Rakitan:

netstandard.dll, System.Net.Requests.dll

Sumber:

HttpWebRequest.cs

Mendapatkan atau mengatur nilai If-Modified-Since header HTTP.

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

Nilai Properti

DateTime

yang DateTime berisi konten If-Modified-Since header HTTP.

Contoh

Contoh kode berikut memeriksa IfModifiedSince properti .

// 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

Keterangan

Hati

WebRequest, , HttpWebRequestServicePoint, dan WebClient usang, dan Anda tidak boleh menggunakannya untuk pengembangan baru. Gunakan HttpClient sebagai gantinya.

If-Modified-Since Jika header adalah null, maka nilai yang dikembalikan akan diatur ke DateTime.MinValue.

Properti IfModifiedSince adalah objek standar System.DateTime dan dapat berisi System.DateTimeKind bidang DateTimeKind.Local, , DateTimeKind.Utcatau DateTimeKind.Unspecified. Setiap jenis waktu dapat diatur saat menggunakan IfModifiedSince properti . Jika DateTimeKind.Unspecified diatur atau diambil, IfModifiedSince properti diasumsikan ( DateTimeKind.Local waktu setempat).

Kelas di System.Net namespace selalu menuliskannya IfModifiedSince pada properti pada kawat selama transmisi dalam bentuk standar menggunakan format GMT (Utc).

IfModifiedSince Jika properti diatur ke DateTime.MinValue, maka If-Modified-Since header HTTP dihapus dari Headers properti dan WebHeaderCollection.

IfModifiedSince Jika properti adalah DateTime.MinValue, ini menunjukkan bahwa If-Modified-Since header HTTP tidak disertakan dalam Headers properti dan WebHeaderCollection.

Nota

Nilai untuk properti ini disimpan dalam WebHeaderCollection. Jika WebHeaderCollection diatur, nilai properti akan hilang.

IfModifiedSince Jika properti diatur dan kode status 304 (Tidak Diubah) dikembalikan, maka akan System.Net.WebException dilemparkan oleh BeginGetResponsemetode , GetResponse, dan EndGetResponse .