Custom pin image in annotationView in iOS

The accepted answer doesn't work, as it has annotationView uninitialized in else block.

Here's a better solution. It dequeues annotation view if possible or creates a new one if not:

// https://stackoverflow.com/a/38159048/1321917
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    // Don't want to show a custom image if the annotation is the user's location.
    guard !(annotation is MKUserLocation) else {
        return nil
    }

    // Better to make this class property
    let annotationIdentifier = "AnnotationIdentifier"

    var annotationView: MKAnnotationView?
    if let dequeuedAnnotationView = mapView.dequeueReusableAnnotationView(withIdentifier: annotationIdentifier) {
        annotationView = dequeuedAnnotationView
        annotationView?.annotation = annotation
    }
    else {
        annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: annotationIdentifier)
        annotationView?.rightCalloutAccessoryView = UIButton(type: .detailDisclosure)
    }

    if let annotationView = annotationView {
        // Configure your annotation view here
        annotationView.canShowCallout = true
        annotationView.image = UIImage(named: "yourImage")
    }

    return annotationView
}

Here is the answer:

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

    let identifier = "MyPin"

    if annotation.isKindOfClass(MKUserLocation) {
        return nil
    }

    let detailButton: UIButton = UIButton(type: UIButtonType.DetailDisclosure)

    if let annotationView = mapView.dequeueReusableAnnotationViewWithIdentifier(identifier) {
        annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: "pin")
        annotationView.canShowCallout = true
        annotationView.image = UIImage(named: "custom_pin.png")
        annotationView.rightCalloutAccessoryView = detailButton
    }
    else {
        annotationView.annotation = annotation
    }

    return annotationView
}

Regards