Some times you may have a page with output cache enabled , and for some reason you don't want to use its output cache ,
Take this seanrio:
you have a page that displays a Dynamic data , and you have 2 users
- Viewers: they just View your page.
- Editors: they need to Edit the data in the page , and they must see the latest changes they did .
and you decided to Enable output Caching on the page to enhance the Performance ,
Now the problem is : the Editors can't Edit and See the Latest chages they did , because the page output is cached ,
you need to enforce the page to show and render the latest data without using its current cached output,and without affecting the current cached output.
The solution :
you need to use HttpCachePolicy.AddValidationCallback Method , so that you can register an output Cache validation Callback ,
Set the Output Caching for your page By setting the output cache in ASPX code as follows:
<%@ OutputCache VaryByParam="none" Duration="600" %>
and in Code behind :
Page_Load:
Public Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
If HttpContext.Current.User.Identity.IsAuthenticated Then
Response.Cache.AddValidationCallback(New HttpCacheValidateHandler(AddressOf ValidateCache), Nothing)
End If
End Sub
And the ValidateCache method:
'' this method will invoked every time the page requested
Public Shared Sub ValidateCache(ByVal Currentcontext As HttpContext, ByVal data As Object, ByRef status As HttpValidationStatus)
If Currentcontext.User.IsInRole("Editors") Then
' Dont use the output cache for the Editors
' and force the page to Excute ( handled as a cache miss)
status = HttpValidationStatus.IgnoreThisRequest
Else
' nothing needed , just use the Output cache
' also if you want to Invalidate the page Output cache ,
' you need to set the status value to HttpValidationStatus.Invalid
End If
End Sub
How to Test :
Add a break point on the Page_laod event Handler, Page_Load will not called for Non Editors Users (Unless the output Cache Expired )
Hope it Helps.
Anas Ghanem