How to custom the image of MKAnnotation pin

I am trying to change the image that is inside the MKAnnotation without removing the rounded shape.

Here I create a custom class of MKAnnotation:

class MapPin: NSObject, MKAnnotation {
    let title: String?
    let locationName: String
    let coordinate: CLLocationCoordinate2D
    init(title: String, locationName: String, coordinate: CLLocationCoordinate2D) {
        self.title = title
        self.locationName = locationName
        self.coordinate = coordinate
    }
}

Here I create a MapPin and I add it to the mapView

func setPinUsingMKAnnotation() {
   let pin1 = MapPin(title: "Here", locationName: "Device Location", coordinate: CLLocationCoordinate2D(latitude: 21.283921, longitude: -157.831661))
   let coordinateRegion = MKCoordinateRegion(center: pin1.coordinate, latitudinalMeters: 800, longitudinalMeters: 800)
   mapView.setRegion(coordinateRegion, animated: true)
   mapView.addAnnotations([pin1])
}

The first image is what I created, the second image is what I would like it to be.

I even implemented MKMapViewDelegate:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    var annotationView = MKAnnotationView()
    annotationView.image = #imageLiteral(resourceName: "heart")
    return annotationView
}

This is the result:

The rounded shape disappears.

I saw many tutorials about how to custom a pin, but they only explained how to put an image instead of the pin (like the hearth image above). I would like to know how to change the image (and color) of the pin and keep the rounded shape (see the blue pin image above).

Any hints? Thanks

If you want that rounded border, you can render it yourself, or easier, subclass MKMarkerAnnotationView rather than MKAnnotationView:

class CustomAnnotationView: MKMarkerAnnotationView {
    override var annotation: MKAnnotation? {
        didSet { configure(for: annotation) }
    }

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

        configure(for: annotation)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func configure(for annotation: MKAnnotation?) {
        glyphImage = ...
        markerTintColor = ...
            
        displayPriority = .required

        // if doing clustering, also add
        // clusteringIdentifier = ...
    }
}

That way, not only do you get the circular border, but you get all of the marker annotation view behaviors (shows the title of the annotation view below the marker, if you select on the marker annotation view, it becomes larger, etc.). There’s a lot of marker annotation view behaviors that you probably don’t want to have to write from scratch if you don’t have to. By subclassing MKMarkerAnnotationView instead of the vanilla MKAnnotationView, you get all those behaviors for free.

For example, you could:

class CustomAnnotationView: MKMarkerAnnotationView {
    static let glyphImage: UIImage = {
        let rect = CGRect(origin: .zero, size: CGSize(width: 40, height: 40))
        return UIGraphicsImageRenderer(bounds: rect).image { _ in
            let radius: CGFloat = 11
            let offset: CGFloat = 7
            let insetY: CGFloat = 5
            let center = CGPoint(x: rect.midX, y: rect.maxY - radius - insetY)
            let path = UIBezierPath(arcCenter: center, radius: radius, startAngle: 0, endAngle: .pi, clockwise: true)
            path.addQuadCurve(to: CGPoint(x: rect.midX, y: rect.minY + insetY), controlPoint: CGPoint(x: rect.midX - radius, y: center.y - offset))
            path.addQuadCurve(to: CGPoint(x: rect.midX + radius, y: center.y), controlPoint: CGPoint(x: rect.midX + radius, y: center.y - offset))
            path.close()
            UIColor.white.setFill()
            path.fill()
        }
    }()

    override var annotation: MKAnnotation? {
        didSet { configure(for: annotation) }
    }

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

        configure(for: annotation)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func configure(for annotation: MKAnnotation?) {
        glyphImage = Self.glyphImage
        markerTintColor = #colorLiteral(red: 0.005868499167, green: 0.5166643262, blue: 0.9889912009, alpha: 1)

        displayPriority = .required

        // if doing clustering, also add
        // clusteringIdentifier = ...
    }
}

That yields:

Obviously, when you set glyphImage, set it to whatever image you want. The old SF Symbols doesn't have that “drop” image (though iOS 14 has drop.fill). But supply whatever 40 × 40 pt image view you want. I'm rendering it myself, but you can use whatever appropriately sized image from your asset catalog (or from the system symbols) that you want.

As an aside, since iOS 11, you wouldn't generally wouldn't implement mapView(_:viewFor:) at all, unless absolutely necessary (which it isn't in this case). For example, you can get rid of your viewFor method and just register your custom annotation view in viewDidLoad:

override func viewDidLoad() {
    super.viewDidLoad()

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

    ...
}