Resize MKAnnotationView Image When map zooms in and out?

Question

What i have

I have about 150 MKAnnotationViews on a map. Every MKAnnotationView has an image that replaces the default pin.

What\'s

Answer 1

@Funktional's answer in Swift 3:

class MapViewController: UIViewController: UIGestureRecognizerDelegate {

    @IBOutlet weak var mapView: MKMapView!

    override func viewDidLoad() {
        super.viewDidLoad()

        // You can also add this gesture recognizer and set the delegate via storyboard
        let pinchGR = UIPinchGestureRecognizer(target: self, action: #selector(handlePinchGesture))
        pinchGR.delegate = self
        self.mapView.addGestureRecognizer(pinchGR)
    }

    // link as @IBAction when added via storyboard
    func handlePinchGesture(_ sender: UIPinchGestureRecognizer) {
        if sender.state == .ended {
            for annotation in mapView.annotations {
                if annotation is MKUserLocation {
                    continue
                }
                guard let annotationView = self.mapView.view(for: annotation) else { continue }
                let scale = -1 * sqrt(1 - pow(mapView.zoomLevel / 20, 2.0)) + 1.4
                annotationView.transform = CGAffineTransform(scaleX: CGFloat(scale), y: CGFloat(scale))
            }
        }
    }

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }
}

extension MKMapView {
    var zoomLevel: Double {
        return log2(360 * ((Double(self.frame.size.width) / 256) / self.region.span.longitudeDelta)) - 1
    }
}