Error setting parameters on cached usercontrol

[Jens]

Hello,

I've created a usercontrol that's cached:
<%@ OutputCache Duration="43200" VaryByParam="none" %>

>From the source page I set some parameters of the control:

UserControl.SubID = 2
UserControl.Subrubriek = "Test"

When I load the page for the first time everything is okay, but when I
reload the page I get an error "Object reference not set to an
instance of an object" on the line "UserControl.SubID = 2"

I think this is because the object is cached when reloading the page.
How can I check if the usercontrol is in cache so I can skip the code
above?

Thanks in advance,
Jens