>>Hi All,
>>
>>How to determine if a property of an object is changed automatically, such as Listbox.Listcount, form.activeobject, I've tried to use assign method, but it didn't work.
>>
>
>I don't think you can do this. For user assigned propreties, you would use an Assign method, but the propreties you mentioned are read-only because they are system assigned. (ActiveControl is not really a property, it is an object reference).

I'd tend to agree - the only thing I can think of would be some sort of a voyeur pattern object that polled the content of the object's native property(ies) being watched and check the current value against the last recorded value. Then trigger a method based on the observed change. It could be done with a timer, but it'd eat cycles, and having at least one per form or container would get expensive quickly.