MKAnnotationView deselected on setRegion - ios

Question

I am trying to zoom in significantly on a pin when a MKAnnotationView is clicked with MapkKit using the following code:
MKCoordinateRegion mapRegion;
mapRegion.center = view.annotation.coordinate;;
mapRegion.span.latitudeDelta = 0.2;
mapRegion.span.longitudeDelta = 0.2;
[MKMapView animateWithDuration:0.15 animations:^{
[mapView setRegion:mapRegion animated: YES];
}];
However, whenever I zoom in I want the pin to remain selected. Is there a way to prevent the MKAnnotatiotionView from being deselected and the function didDeselectAnnotationView from being called.
I think the reason it might be happening is because the mapView on the zoom is updating the annotations. Is there a way to prevent this from happening if this is the cause?

Answer 1

Yes, if [mapView setRegion: ...] causes the annotations on the mapView to change for whatever reason, then your selected annotation will be deselected (because it's about to be removed!).
One way to fix this is to do a 'diff' replace of your annotations. For example, at the moment you might have some code that looks like (expressed in Swift):
func displayNewMapPins(pinModels: [MyCustomPinModel]) {
self.mapView.removeAnnotations(self.mapView.annotations) //remove all of the currently displayed annotations
let newAnnotations = annotationModels.map { $0.toAnnotation } //convert 'MyCustomPinModel' to an 'MKAnnotation'
self.mapView.addAnnotations(newAnnotations) //put the new annotations on the map
}
You want to change it to be more like this:
func displayNewMapPins(pinModels: [MyCustomPinModel]) {
let oldAnnotations = self.mapView.annotations
let newAnnotations = annotationModels.map { $0.toAnnotation }
let annotationsToRemove = SomeOtherThing.thingsContainedIn(oldAnnotations, butNotIn: newAnnotations)
let annotationsToAdd = SomeOtherThing.thingsContainedIn(newAnnotations, butNotIn: oldAnnotations)
self.mapView.removeAnnotations(annotationsToRemove)
self.mapView.addAnnotations(annotationsToAdd)
}
The exact implementation of SomeOtherThing.thingsContainedIn(:butNotIn:) depends on your requirements, but this is the general code structure you want to aim for.
Doing it this way will have an added benefit of improving the performance of your app - adding and removing annotations from a MKMapView can be really expensive!