HttpCachePolicy.AddValidationCallback Method (HttpCacheValidateHandler, Object)


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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


Type: System.Web.HttpCacheValidateHandler

The HttpCacheValidateHandler value.

Type: System.Object

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

Exception Condition

The specified handler is null.

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.

AddValidationCallback is introduced in the .NET Framework version 3.5. For more information, see .NET Framework Versions and Dependencies.

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;


.NET Framework
Available since 1.1
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