add observer on annotationView, call once in simulator 4.0

Question

hi, i add annotationView on the mapView then for each annotation i add a observer: problem when i call the observer by the action click on annotationView, it response only once and then do nothing the second time.(PS: this happen only on simulator 4.0 and 4.1) that is the code that i use. BOOL annotationAppeared = [[change valueForKey:NSKeyValueChangeNewKey] boolValue];

THX for your help. because of u maybe i application will work fine this time......