如何在iPhone中的地图视图中心添加注释？

import MapKit

class ViewController: UIViewController, MKMapViewDelegate {
    
    @IBOutlet weak var mapView: MKMapView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        mapView.delegate = self
        
        // 创建自定义注释对象
        let annotation = CustomAnnotation(title: "这是标题", subtitle: "这是副标题", coordinate: CLLocationCoordinate2D(latitude: 37.331686, longitude: -122.030656))
        
        // 将注释对象添加到地图视图中
        mapView.addAnnotation(annotation)
        
        // 设置地图视图的中心和缩放级别
        let region = MKCoordinateRegion(center: annotation.coordinate, latitudinalMeters: 1000, longitudinalMeters: 1000)
        mapView.setRegion(region, animated: true)
    }
    
    // 自定义注释视图
    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 = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
                annotationView?.canShowCallout = true
            } else {
                annotationView?.annotation = annotation
            }
            
            return annotationView
        }
        
        return nil
    }
}

// 自定义注释对象
class CustomAnnotation: NSObject, MKAnnotation {
    var title: String?
    var subtitle: String?
    var coordinate: CLLocationCoordinate2D
    
    init(title: String, subtitle: String, coordinate: CLLocationCoordinate2D) {
        self.title = title
        self.subtitle = subtitle
        self.coordinate = coordinate
    }
}