previous value of NSControl

FROM : norio ota
DATE : Sat Mar 15 02:20:12 2008

Hi,

I feel that Carbon gave us the chance to get its previous value right 
after the value is changed using Carbon Event.
How do I get the previous value in Cocoa?
I set an action to a NSDatePicker and I'd like to know if an input 
value , especially year component, is different from the year of its 
previous date in the action method, without having a placeholder for 
the previous value.

Thanks,
Norio Ota