Google maps swift 3中的谷歌地图中未显示路径

我想在谷歌地图中显示路径。但我无法指明我的道路。请帮帮我。这是我的密码。我在斯威夫特花了很多时间。任何帮助都将不胜感激。提前谢谢

let camera = GMSCameraPosition.camera(withLatitude: 48.4843822562792, longitude: 35.0635632500052, zoom: 6)
               let mapView = GMSMapView.map(withFrame: .zero, camera: camera)
        self.view = mapView

        let manager = AFHTTPSessionManager()



        manager.requestSerializer = AFJSONRequestSerializer()

        manager.responseSerializer.acceptableContentTypes =  nil

        let urlString = "https://maps.googleapis.com/maps/api/directions/json?origin=48.4843822562792,35.0635632500052&destination=48.4893899423081,35.0640017911792&waypoints=48.4833428800255,35.0710221379995|48.4887622031403,35.0573639944196&key=AIzaSyDvS9TbaQ1WzP_3YX6TBrjoTNGhnFa0MBY"


        let urlwithPercentEscapes = urlString.addingPercentEncoding( withAllowedCharacters: .urlQueryAllowed)



        manager.get(urlwithPercentEscapes!, parameters: nil, success: { (operation, response) in

             let parsedData = JSON(response)


                        var path = GMSPath.init(fromEncodedPath: parsedData["routes"][0]["overview_polyline"]["points"].string!)
                        //GMSPath.fromEncodedPath(parsedData["routes"][0]["overview_polyline"]["points"].string!)

            print(path!)

                        var singleLine = GMSPolyline.init(path: path)
                        singleLine.strokeWidth = 7
                        singleLine.strokeColor = UIColor.green
                        singleLine.map = self.mapView


        }, failure: { (operation, error) in


        })

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