Axapta Form

Hi Friends

I have a form having overview & general tab. There are two  fields say A & B which are present  on both tabs.

A is a enum type field. When A=0 i want to enable field B and when A=1 then B is disabled. I can do it by writing codes on modified of control at both places, but I want to write code at one place that will work in all tab.

How to do this?

pls help

Thanks