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HttpCacheValidateHandler Delegate

Represents a method that is called to validate a cached item before the item is served from the cache.

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

Public Delegate Sub HttpCacheValidateHandler ( _
	context As HttpContext, _
	data As Object, _
	ByRef validationStatus As HttpValidationStatus _
Dim instance As New HttpCacheValidateHandler(AddressOf HandlerMethod)
/** @delegate */
public delegate void HttpCacheValidateHandler (
	HttpContext context, 
	Object data, 
	/** @ref */ HttpValidationStatus validationStatus
JScript supports the use of delegates, but not the declaration of new ones.



The HttpContext object containing information about the current request.


User-supplied data used to validate the cached item.


An HttpValidationStatus enumeration value. Your delegate should set this value to indicate the result of the validation.

If a cached item is invalidated within the scope of the HttpCacheValidateHandler method, it is evicted from the cache and the request for the item is treated as a cache miss.

How to: Check the Validity of a Cached PageBuilding ASP .NET Web Applications
How to: Check the Validity of a Cached PageBuilding ASP .NET Web Applications

The following code example demonstrates how to add a new cache validation delegate to an application.

Private Sub Page_Load(sender As Object, e As EventArgs)
   Response.Cache.AddValidationCallback(New HttpCacheValidateHandler(AddressOf CacheValidate1), Nothing)
End Sub
Public Sub CacheValidate1(context As HttpContext, data As Object, ByRef status As HttpValidationStatus)
   If context.Request.QueryString("Valid") = "false" Then
      status = HttpValidationStatus.Invalid
      status = HttpValidationStatus.Valid
   End If
End Sub

    private void Page_Load(Object sender, EventArgs e)
            new HttpCacheValidateHandler(CacheValidate1), null);
    } //Page_Load

    public void CacheValidate1(HttpContext context, Object data,
        /**@ref*/HttpValidationStatus status)
        if (context.get_Request().get_QueryString().get_Item("Valid").
            Equals("false")) {
            status = HttpValidationStatus.Invalid;
        else {
            status = HttpValidationStatus.Valid;
    } //CacheValidate1
} //Page1 

Windows 98, Windows 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

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