我已经设置了implemented GMSMapViewDelegate，并将其设置为self，但仍然无法使任何委托函数工作。下面是我的代码示例：

class UserViewController: UIViewController, CLLocationManagerDelegate, GMSMapViewDelegate {

    var mapView: GMSMapView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        if mapView == nil {
            mapView = GMSMapView()
        }

        mapView.delegate = self

    }

    func mapView(mapView: GMSMapView, didChangeCameraPosition position: GMSCameraPosition) {
        print(position)
    }

    func mapView(mapView: GMSMapView, willMove gesture: Bool) {
        print(gesture)
    }

    func mapView(mapView: GMSMapView, idleAtCameraPosition position: GMSCameraPosition) {
        print(position)
    }

所有mapView函数都没有打印任何内容。我已经检查了委托并知道它设置正确。我是否遗漏了什么？