- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    static NSString *identifier = @"HPIPAnnotation";

    if ([annotation isKindOfClass:[CoreCityAnnotation class]])
    {
        MKPinAnnotationView *annotationView = (MKPinAnnotationView *) [_mapView dequeueReusableAnnotationViewWithIdentifier:identifier];
        if (annotationView == nil) {
            annotationView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:identifier];
        } else {
            annotationView.annotation = annotation;
        }

        UIButton *disclosureButton = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];

        annotationView.canShowCallout = YES;
        annotationView.animatesDrop = YES;

        annotationView.rightCalloutAccessoryView = disclosureButton;

    return annotationView;

    }

    return nil;
}

那是我对代表的实现.