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HttpCachePolicy.AddValidationCallback Method

Registers a validation callback for the current response.

Namespace: System.Web
Assembly: System.Web (in system.web.dll)

public void AddValidationCallback (
	HttpCacheValidateHandler handler,
	Object data
public void AddValidationCallback (
	HttpCacheValidateHandler handler, 
	Object data
public function AddValidationCallback (
	handler : HttpCacheValidateHandler, 
	data : Object
Not applicable.



The HttpCacheValidateHandler value.


The arbitrary user-supplied data that is passed back to the AddValidationCallback delegate.

Exception typeCondition


The specified handler is a null reference (Nothing in Visual Basic).

TheAddValidationCallback method provides a mechanism to check the response programmatically in the cache before the response is returned to the client by the output cache.

Before the response is served from the Web server cache, all registered handlers are queried to ensure resource validity. If any handler sets a flag indicating that the cached response is not valid, the entry is marked as not valid and expelled from the cache. In this case, as well as when any handler indicates that the cached response should be ignored for this request, the request is then handled as if it were a cache miss.

The following code example demonstrates how to add a delegate to validate a request based on query string values.

<%@ Page Language="C#" %>
<%@ OutputCache VaryByParam="none" Duration="600" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

<script language="c#" runat="server">

   static string validationstate;
   public void Page_Load()
      Response.Cache.AddValidationCallback(new HttpCacheValidateHandler(ValidateCache), null);
      stamp.InnerHtml = DateTime.Now.ToString("r");

   public static void ValidateCache(HttpContext context, Object data, ref HttpValidationStatus status) 
      if (context.Request.QueryString["Valid"] == "false") 
         status = HttpValidationStatus.Invalid;
      else if (context.Request.QueryString["Valid"] == "ignore") 
         status = HttpValidationStatus.IgnoreThisRequest;
         status = HttpValidationStatus.Valid;


Windows 98, Windows Server 2000 SP4, 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

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