如何在swift中沿多段线移动标记

import MapKit

class ViewController: UIViewController, MKMapViewDelegate {
    @IBOutlet weak var mapView: MKMapView!
    
    var annotation: MKPointAnnotation!
    var polyline: MKPolyline!
    var polylineRenderer: MKPolylineRenderer!
    var polylineCoordinates: [CLLocationCoordinate2D] = []
    var currentIndex: Int = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置地图视图的代理
        mapView.delegate = self
        
        // 创建标记
        annotation = MKPointAnnotation()
        annotation.coordinate = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)
        mapView.addAnnotation(annotation)
        
        // 创建多段线坐标点
        polylineCoordinates.append(CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194))
        polylineCoordinates.append(CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4313))
        polylineCoordinates.append(CLLocationCoordinate2D(latitude: 37.7838, longitude: -122.4313))
        polylineCoordinates.append(CLLocationCoordinate2D(latitude: 37.7838, longitude: -122.4194))
        
        // 创建多段线
        polyline = MKPolyline(coordinates: polylineCoordinates, count: polylineCoordinates.count)
        
        // 将多段线添加到地图视图
        mapView.addOverlay(polyline)
        
        // 开始移动标记
        moveAnnotation()
    }
    
    // 移动标记
    func moveAnnotation() {
        let annotationAnimation = CABasicAnimation(keyPath: "coordinate")
        annotationAnimation.duration = 10.0
        annotationAnimation.timingFunction = CAMediaTimingFunction(name: .linear)
        annotationAnimation.fromValue = NSValue(mkCoordinate: polylineCoordinates[currentIndex])
        annotationAnimation.toValue = NSValue(mkCoordinate: polylineCoordinates[currentIndex + 1])
        annotationAnimation.delegate = self
        
        annotation.add(annotationAnimation, forKey: "coordinate")
    }
    
    // 动画结束时调用
    override func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        currentIndex += 1
        
        if currentIndex < polylineCoordinates.count - 1 {
            moveAnnotation()
        }
    }
    
    // 渲染多段线
    func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        if overlay is MKPolyline {
            if polylineRenderer == nil {
                polylineRenderer = MKPolylineRenderer(overlay: overlay)
                polylineRenderer.strokeColor = UIColor.blue
                polylineRenderer.lineWidth = 3.0
            }
            return polylineRenderer
        }
        
        return MKOverlayRenderer()
    }
}