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VaryByControl Caching problem w/ User Control & Properties
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Curtis Swartzentruber
-- Moved from [aspngfreeforall] to [aspngcache] by Marcie Jones <Click here to reveal e-mail address> --

Hi,

This might be better on the caching list or usercontrol
list, but not sure where. I have run into an issue that
appears to be caching-related as it only happens when
caching is enabled in my user control.

Here is the scenerio:

We run a music retail site, so a lot of content is based
on a particular genre. This is a perfect use for a user
control, with GenreID as a public property. First of all,
I want to make sure I am understanding the VaryByControl
param (can this be based on a public property of the control?)

Anyway, I am building a way to browse titles by genre and
obviously want to use caching since the paging and data
access can be expensive. I created a user control which
renders the "Sub Genres" of a particular Genre at the top
of a datagrid. If I try to cache this control, the first
time it is called it will render. If I browse to a new
GenreID, the call on that page fails with:

Object reference not set to an instance of an object.

at the point I am setting the GenreID property of the user
control. The same code works perfectly if I don't cache
the user control. Now I could probably use page level
caching to get around this, but I want to understand what
is going on.

Notes:

Main page is using VB code-behind
Control is using VB code-behind
Reference to user control is set in code-behind of main page
Property is being set in the Page_Load, using standard
    If Not Page.IsPostback

I'm curious if anyone can duplicate this problem. At this
point it seems to either be a misunderstanding on my part on
how to use varybycontrol caching or a bug.

Thanks,

Curtis
Reply to this message...
 
    
John Crim
AFAIK, you can't programatically set a property on a cached control,
because that control isn't actually created when cached output is used.
There probably is a way to do it, I just don't know how off the top of
my head.

However,
<TitlesUserControl Genre="xx" id="controlName">
Is legal. Genre must be a string property on the user control.

VaryByControl and VaryByParam do _not_ allow varying output by a
property of the control - they are both used to vary by the query string
or POST params. Additionally, VaryByControl allows you to cache output
for a specific user control name (id).

Regards,

John Crim
WebGecko Software
http://www.webgecko.com

-----Original Message-----
From: Curtis Swartzentruber [mailto:Click here to reveal e-mail address]

We run a music retail site, so a lot of content is based
on a particular genre. This is a perfect use for a user control, with
GenreID as a public property. First of all, I want to make sure I am
understanding the VaryByControl param (can this be based on a public
property of the control?)

Anyway, I am building a way to browse titles by genre and obviously want
to use caching since the paging and data access can be expensive. I
created a user control which renders the "Sub Genres" of a particular
Genre at the top of a datagrid. If I try to cache this control, the
first time it is called it will render. If I browse to a new GenreID,
the call on that page fails with:
Reply to this message...
 
 
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