如何检测MKMapView被缩小/缩小？

- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated {
    mapRegion = mapView.region; //MKCoordinateRegion myRegion in .h
}

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated {

      MKCoordinateRegion newRegion = mapView.region;

    if (mapRegion.span.latitudeDelta != newRegion.span.latitudeDelta ||
       mapRegion.span.longitudeDelta != newRegion.span.longitudeDelta){

        NSLog(@"The zoom has changed");        
  }
}