UI Panel event-handling callbacks

[mads]

I'm Doing a UI Panel to manipulate the Layers of the current selected Composition. So I need to refresh it when im going to use it. To display the Layers of the
current selected comp(Which could be changed). Right now i have a refresh button. But I was thinking if there was a event- handling like window.onActive() or windoe.onCurserEntering().
So the UI Panel was automatically updated when I should use it. when I activate It. I'm Using CS4. but would also like to make it work in CS3.
-Mads

[nab]

As far as I know a script can't be aware of such dependencies.