(Swift 3)如何向MapView添加多个引脚

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

let mapView = MKMapView(frame: CGRect(x: 0, y: 0, width: 300, height: 300))
mapView.delegate = self

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    if annotation is MKUserLocation {
        return nil
    }
    
    let pinView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "pin")
    pinView.pinTintColor = UIColor.red
    pinView.canShowCallout = true
    
    return pinView
}

let annotation1 = CustomAnnotation(coordinate: CLLocationCoordinate2D(latitude: 37.331686, longitude: -122.030656), title: "Apple Park")
let annotation2 = CustomAnnotation(coordinate: CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194), title: "Golden Gate Bridge")

mapView.addAnnotations([annotation1, annotation2])