如何在Mapkit中获取注释索引？

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    if annotation is MKUserLocation {
        return nil
    }
    
    let annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "pin")
    annotationView.tag = annotationIndex // 将annotationIndex设置为注释的索引值
    return annotationView
}

func getAnnotationIndex() -> Int? {
    guard let selectedAnnotations = mapView.selectedAnnotations else {
        return nil
    }
    
    for annotation in selectedAnnotations {
        if let annotationView = mapView.view(for: annotation), let index = annotationView.tag {
            return index // 返回注释索引
        }
    }
    
    return nil
}