Using custom annotation views in MKMapView

If you want to display completely custom views as “pins” on the map in your iOS application, you should use annotations. All your data needs to be represented as objects conforming to the MKAnnotation protocol, with title, subtitle and coordinate as the required properties.

Custom view implementation

Visually you represent an MKAnnotation with a MKAnnotationView. You can create a custom class that subclasses MKAnnotationView and implement your custom UI in that class.

Here is an sample MKAnnotationView with fixed size that displays just one custom view

final class LocationAnnotationView: MKAnnotationView, Reusable {

    // MARK: Initialization

    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)

        frame = CGRect(x: 0, y: 0, width: 40, height: 50)
        centerOffset = CGPoint(x: 0, y: -frame.size.height / 2)

        canShowCallout = true
        setupUI()
    }

    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: Setup

    private func setupUI() {
        backgroundColor = .clear

        let view = MapPinView()
        addSubview(view)

        view.frame = bounds
    }
}

The MKAnnotationView is by default aligned to its corresponding position on map with the bottom left corner. If your MKAnnotationView looks like a pin for example, you need to align it to the position on the map with the bottom center point. To do that you use the centerOffset property as shown.

Registering the custom view with MKMapView

The next step is to tell MKMapView to user your custom class.

Using single custom MKAnnotationView

If you want to display only one type of annotation in your MKMapView, just register your custom class with the MKMapViewDefaultAnnotationViewReuseIdentifier reuse identifier

mapView.register(LocationAnnotationView.self, forAnnotationViewWithReuseIdentifier: MKMapViewDefaultAnnotationViewReuseIdentifier)

This is enough to make MKMapView to completely handle creating and recycling instances of your custom MKAnnotationViews for you. No need to implement any MKMapView delegate methods for providing annotation views.

Using multiple custom MKAnnotationViews

If you want to use multiple types of annotations in your MKMapView, you need to register them all with different reuse identifiers.

mapView.register(LocationAnnotationView.self, forAnnotationViewWithReuseIdentifier: LocationAnnotationView.reuseIdentifier)
mapView.register(LiveLocationDataMapAnnotationView.self, forAnnotationViewWithReuseIdentifier: LiveLocationDataMapAnnotationView.reuseIdentifier)

I use the Reusable library that automatically provides reuse identifiers but you can use any reusable identifier string you like

Next you need to implement the mapView(_:viewFor:) method of the MKMapViewDelegate and decide which of those custom MKAnnotationViews is used for which MKAnnotation

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    switch annotation {    
    case is LocationViewModel:
        return mapView.dequeueReusableAnnotationView(withIdentifier: LocationAnnotationView.reuseIdentifier, for: annotation)
    case is LiveLocationDataViewModel:
        return mapView.dequeueReusableAnnotationView(withIdentifier: LiveLocationDataMapAnnotationView.reuseIdentifier, for: annotation)    
    default:        
        return nil
    }
}

Just do not forget to set the MKMapView delegate to nil in your view controller deinit method as it might cause some strange crashes.