IOS Google地图标记标题未显示

let marker = GMSMarker()
marker.position = CLLocationCoordinate2D(latitude: 37.785834, longitude: -122.406417)
marker.title = "San Francisco"
marker.map = mapView

func mapView(_ mapView: GMSMapView, markerInfoWindow marker: GMSMarker) -> UIView? {
    let infoWindow = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 70))
    infoWindow.backgroundColor = UIColor.white
    
    let titleLabel = UILabel(frame: CGRect(x: 10, y: 10, width: 180, height: 20))
    titleLabel.text = marker.title
    infoWindow.addSubview(titleLabel)
    
    return infoWindow
}