如何在SwiftUI / Mapkit中正确显示自定义引脚？

import SwiftUI
import MapKit

struct CustomAnnotation: Identifiable, MKAnnotation {
    var id = UUID()
    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?
}

struct MapView: UIViewRepresentable {
    @State private var region = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: 37.331516, longitude: -122.030028), span: MKCoordinateSpan(latitudeDelta: 0.2, longitudeDelta: 0.2))
    
    var annotations: [CustomAnnotation]
    
    func makeUIView(context: Context) -> MKMapView {
        let mapView = MKMapView()
        mapView.delegate = context.coordinator
        mapView.setRegion(region, animated: true)
        return mapView
    }
    
    func updateUIView(_ view: MKMapView, context: Context) {
        view.removeAnnotations(view.annotations)
        view.addAnnotations(annotations)
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject, MKMapViewDelegate {
        var parent: MapView
        
        init(_ parent: MapView) {
            self.parent = parent
        }
        
        func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
            guard annotation is CustomAnnotation else {
                return nil
            }
            
            let identifier = "CustomAnnotation"
            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier)
            
            if annotationView == nil {
                annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
                annotationView?.canShowCallout = true
            } else {
                annotationView?.annotation = annotation
            }
            
            return annotationView
        }
    }
}

struct ContentView: View {
    var body: some View {
        MapView(annotations: [
            CustomAnnotation(coordinate: CLLocationCoordinate2D(latitude: 37.331516, longitude: -122.030028), title: "Apple Park", subtitle: "Cupertino, CA"),
            CustomAnnotation(coordinate: CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194), title: "Golden Gate Bridge", subtitle: "San Francisco, CA")
        ])
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}