How can I tell when an MKOverlay is no longer within view?

问题

MKMapViewDelegate's mapView:rendererForOverlay fires when an MKOverlay's boundingMapRect enters the visible bounds of the MKMapView.

Is there an equivalent delegate method that is fired when the MKOverlay leaves the map view's visible bounds? Or do I have to do this math myself?

来源：https://stackoverflow.com/questions/23147789/how-can-i-tell-when-an-mkoverlay-is-no-longer-within-view