我正在尝试获取当前用户位置的CLLocationManager示例的经纬度坐标。
在我的viewWillAppear方法中有这两行代码：

locationManager = CLLocationManager()
locationManager.requestWhenInUseAuthorization()

然后我有一个名为startRoute的方法来计算从当前位置到Map上某个特定注解的路线。然后我在这些路径之间绘制路线。不幸的是，这是与Map上的两个注解一起工作的，但我不能让它与用户的当前位置和一些注解一起工作。
我尝试了下面的脚本，但当我打印print("LAT \(currentLocation.coordinate.latitude)")时，它会给予我0.0作为结果。

func startRoute() {
        // Set the latitude and longtitude of the locations (markers)
        let sourceLocation = CLLocationCoordinate2D(latitude: currentLocation.coordinate.latitude, longitude: currentLocation.coordinate.longitude)
        let destinationLocation = CLLocationCoordinate2D(latitude: sightseeing.latitude!, longitude: sightseeing.longitude!)
        // Create placemark objects containing the location's coordinates
        let sourcePlacemark = MKPlacemark(coordinate: sourceLocation, addressDictionary: nil)
        let destinationPlacemark = MKPlacemark(coordinate: destinationLocation, addressDictionary: nil)
        // MKMapitems are used for routing. This class encapsulates information about a specific point on the map
        let sourceMapItem = MKMapItem(placemark: sourcePlacemark)
        let destinationMapItem = MKMapItem(placemark: destinationPlacemark)
        // Annotations are added which shows the name of the placemarks
        let sourceAnnotation = MKPointAnnotation()
        sourceAnnotation.title = "Times Square"
        if let location = sourcePlacemark.location {
            sourceAnnotation.coordinate = location.coordinate
        }
        let destinationAnnotation = MKPointAnnotation()
        destinationAnnotation.title = "Title"
        destinationAnnotation.subtitle = "Subtitle"
        if let location = destinationPlacemark.location {
            destinationAnnotation.coordinate = location.coordinate
        }
        // The annotations are displayed on the map
        self.mapView.showAnnotations([sourceAnnotation,destinationAnnotation], animated: true )
        // The MKDirectionsRequest class is used to compute the route
        let directionRequest = MKDirectionsRequest()
        directionRequest.source = sourceMapItem
        directionRequest.destination = destinationMapItem
        directionRequest.transportType = .walking
        // Calculate the direction
        let directions = MKDirections(request: directionRequest)
        // The route will be drawn using a polyline as a overlay view on top of the map.
        // The region is set so both locations will be visible
        directions.calculate {
            (response, error) -> Void in
            guard let response = response else {
                if let error = error {
                    print("Error: \(error)")
                }
                return
            }
            let route = response.routes[0]
            self.mapView.add((route.polyline), level: MKOverlayLevel.aboveRoads)
            let rect = route.polyline.boundingMapRect
            self.mapView.setRegion(MKCoordinateRegionForMapRect(rect), animated: true)
        }
    }

在顶部，直接在类声明之后，我创建了对location manager和'CLLocation'的引用：

var locationManager: CLLocationManager!
var currentLocation = CLLocation()

毕竟，这是行不通的。只有当我将sourceLocation更改为硬编码坐标时，它才会绘制到目的地的路线。我做错了什么，或者我遗漏了什么？