Handle the same event from multiple pages in one function

I've got some list boxes on every page in my sight. I want to populate them onload and take action when someone changes the value in them.

 I would rather not have to add code to every pages CodeFile to do this. I know i can toss the code in a class and just call the class in the CodeFile but that would still require changes to every page.

 Is there a way to globally handle events?

 I need a "class" that will handle the ListBox load and change no matter what page loads it or changes it.
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