iOS谷歌地图:如何“保持”标记？Swift 4

import GoogleMaps

class MapViewController: UIViewController {
    var mapView: GMSMapView!
    var markers: [GMSMarker] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建地图视图
        let camera = GMSCameraPosition.camera(withLatitude: 37.7749, longitude: -122.4194, zoom: 12.0)
        mapView = GMSMapView.map(withFrame: view.bounds, camera: camera)
        view.addSubview(mapView)
        
        // 添加标记
        let marker = GMSMarker()
        marker.position = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)
        marker.title = "San Francisco"
        marker.map = mapView
        
        // 保持标记
        markers.append(marker)
    }
}