将自定义注释类调用到viewForAnnotation中

class CustomAnnotation: NSObject, MKAnnotation {
    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?
    
    init(coordinate: CLLocationCoordinate2D, title: String?, subtitle: String?) {
        self.coordinate = coordinate
        self.title = title
        self.subtitle = subtitle
    }
}

class ViewController: UIViewController, MKMapViewDelegate {
    @IBOutlet weak var mapView: MKMapView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        mapView.delegate = self
        
        // 添加自定义标注点
        let annotation = CustomAnnotation(coordinate: CLLocationCoordinate2D(latitude: 37.331705, longitude: -122.030237), title: "Apple Park", subtitle: "Cupertino, CA")
        mapView.addAnnotation(annotation)
    }
    
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if annotation is CustomAnnotation {
            let identifier = "CustomAnnotation"
            
            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier)
            if annotationView == nil {
                annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: identifier)
                annotationView?.canShowCallout = true
                annotationView?.image = UIImage(named: "custom_pin")
            } else {
                annotationView?.annotation = annotation
            }
            
            return annotationView
        }
        
        return nil
    }
}