Changewatcher in flex3.0?how to use in below mentioned Situation

Question

Hello to all,

Please tell me about the change watcher in flex. i have a situation like,

i have few canvas, on which i have to show select and unselect,(These canvas hold product thumbnail images) , so when some thumbnail is selected i have to show selection and on selecting other, i have to unselect the previously selected canvas and have to select other

here rollover and rollout on canvas are also working

Here i have to use changewatcher, as one canvas lost the selection and next gets the selection, so some changewatcher gets called

so pleasse if n e one has done this, plzz help me

thanx in Advance

tc