Right Callout Accessory method and implementation

Question

I was wondering if anyone could tell me how to add a right callout accessory to a map annotation. everything i try doesn't seem to be getting anywhere, so any help would be appreciated.

EDIT

I have tried this line of code but nothing different happens to the annotation.

- (MKAnnotationView *)mapview:(MKMapView *)sender viewForAnnotation:(id <MKAnnotation>)annotation 
{
MKAnnotationView *aView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@""];
aView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
aView.canShowCallout = YES;
aView.annotation = annotation;
return aView;
}