Annotation callout not working Swift

Question

I'm trying to add a callout to my annotations in MapKit, but I cannot get it working after searching quite a bit online.

This is how I am currently creating each annotation which works fine at the moment.

struct loc {
    let title: String
    let latitude: Double
    let longitude: Double
    let phone: Int
    //let subTitle: String
}

var locs = [
    loc(title: "New York, NY",    latitude: 40.713054, longitude: -74.007228, phone: 2334), //subTitle: "Sub title"),
    ]

func placeAnnotations() {
    let annotations = locs.map { location -> MKAnnotation in
        let annotation = MKPointAnnotation()
        annotation.title = location.title
        annotation.coordinate = CLLocationCoordinate2D(latitude: location.latitude, longitude: location.longitude)

        //annotation.subtitle = location.subTitle
        return annotation
    }
    mapView.addAnnotations(annotations)
}

(I have a function which adds data to the array locs)

And this is what I have got when trying to add a callout which isn't working.

func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -> MKAnnotationView? {
    if annotation is MKUserLocation { return nil }
    let identifier = "pin"
    var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier) as? MKPinAnnotationView
    if annotationView == nil {
        annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
        annotationView?.canShowCallout = true
        annotationView?.rightCalloutAccessoryView = UIButton(type: .infoDark)
    } else {
        annotationView?.annotation = annotation
    }

    return annotationView
}

Answer 1

You use:

func mapView(mapView: MKMapView!, viewForAnnotation annotation: MKAnnotation!) -> MKAnnotationView!

That will certainly never be called. In Swift 3, the correct signature is:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView?