>>>Why don't you make a class derived from textbox, add a property, in When method save old value to the property, in Valid... etc.?
>>
>>Good idea. This is probably what I'll do. Thanks.
>
>Well, now I'm sure that this is not what you're looking for. :-)

In the first approach, I'll probably add a property on each of my class control to handle the value from the When() to the Valid(). Yes, this is what I was looking for. :)