(iPhone)如何使用OS 4.0 MapKit实现可拖动的引脚？

import MapKit

class ViewController: UIViewController, MKMapViewDelegate {
    var mapView: MKMapView!
    var pinAnnotation: MKPointAnnotation!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建地图视图
        mapView = MKMapView(frame: view.bounds)
        mapView.delegate = self
        view.addSubview(mapView)
        
        // 添加引脚
        pinAnnotation = MKPointAnnotation()
        pinAnnotation.coordinate = CLLocationCoordinate2D(latitude: 37.331705, longitude: -122.030237)
        mapView.addAnnotation(pinAnnotation)
        
        // 添加拖动手势
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
        mapView.addGestureRecognizer(panGesture)
    }
    
    @objc func handlePan(_ gesture: UIPanGestureRecognizer) {
        let location = gesture.location(in: mapView)
        let coordinate = mapView.convert(location, toCoordinateFrom: mapView)
        
        // 更新引脚坐标
        pinAnnotation.coordinate = coordinate
    }
    
    // MKMapViewDelegate方法，自定义引脚视图
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if annotation is MKPointAnnotation {
            let pinView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: nil)
            pinView.isDraggable = true
            return pinView
        }
        return nil
    }
}