Flex :: Tell If An Object Has Been Modified Since Save?

I'm creating an air application that allows the user to create, edit and save Objects in files. I'm trying to implement a "Save on Close" prompt if the user hasn't saved her changes to the object before closing.Let's say I have a Class called MyClass marked as Bindable that is composed of fields, each exposing a getter and setter. Some of these fields are ArrayCollections of custom Classes. I want to consider a change a change to any of the fields, or any of the fields in any of the objects in any of the array collections the parent object is made up of.

I could manually dispatch an event anytime a setter is called on the MyClass object and manage this all manually, but I'd also have to do it in a bunch of places in the application logic, for instance when the user changes one of the custom objects in one of the array collections that comprises it. This is a fine solution, but a little dirty and hard to maintain. I could also check the current object against a copy I made at the time of start up or last save, but I don't like the idea of doubling my memory footprint just for this.

there was some event, perhaps an event that the binding broadcasts, that I could listen for in one place and manage my "Saved" variable. Does such a thing exist? I tried listening for the dataChange event that binding apparently dispatches, but I either did it wrong, or it doesn't do what I think it should.