为什么路线没有使用以下代码在地图上绘制？

Question

任何人都可以提供帮助 - 以下代码适用于所有方面，除了路线折线没有在地图上绘制 - 你能告诉我我缺少什么吗？

我一直在这个特定的树上走了很长一段时间 - 大声笑

import UIKit
import MapKit

protocol HandleMapSearch: class {
func dropPinZoomIn(_ placemark:MKPlacemark)
}

class ViewController: UIViewController {

var selectedPin: MKPlacemark?
var resultSearchController: UISearchController!

let locationManager = CLLocationManager()

@IBOutlet weak var mapView: MKMapView!

override func viewDidLoad() {
    super.viewDidLoad()

    // Setup Location Manager Variables

    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.requestWhenInUseAuthorization()
    locationManager.requestLocation()

    //Setup Search Bar and Table

    let locationSearchTable = storyboard!.instantiateViewController(withIdentifier: "LocationSearchTable") as! LocationSearchTable
    resultSearchController = UISearchController(searchResultsController: locationSearchTable)
    resultSearchController.searchResultsUpdater = locationSearchTable
    let searchBar = resultSearchController!.searchBar
    searchBar.sizeToFit()
    searchBar.placeholder = "Do You Know Where You're Going To LA LA LA?"
    navigationItem.titleView = resultSearchController?.searchBar
    resultSearchController.hidesNavigationBarDuringPresentation = false
    resultSearchController.dimsBackgroundDuringPresentation = true
    definesPresentationContext = true
    locationSearchTable.mapView = mapView
    locationSearchTable.handleMapSearchDelegate = self
}
}

extension ViewController : CLLocationManagerDelegate {

// Find PolicyHolders current Location

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    guard let location = locations.first else { return }
    let distancespan: CLLocationDegrees = 2000
    let PolicyHolderLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude)

    mapView.setRegion(MKCoordinateRegionMakeWithDistance(PolicyHolderLocation, distancespan, distancespan), animated:  true)

    // Drop pin at Policyholders current Location

    let PolicyHolderPin = Annotation(title: "Title", subtitle: "subtitle", coordinate: PolicyHolderLocation)
    mapView.addAnnotation( PolicyHolderPin )
    print (PolicyHolderLocation)
}

func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
    print("error:: \(error)")
}
}

// Show queried location on map

extension ViewController: HandleMapSearch {

func dropPinZoomIn(_ placemark: MKPlacemark){
    // cache the pin
    selectedPin = placemark
    // clear existing pins
    //mapView.removeAnnotations(mapView.annotations)
    let annotation = MKPointAnnotation()
    annotation.coordinate = placemark.coordinate
    annotation.title = placemark.name

    if let city = placemark.locality,
        let state = placemark.administrativeArea {
        annotation.subtitle = "\(city) \(state)"
    }

    mapView.addAnnotation(annotation)
    let span = MKCoordinateSpanMake(0.05, 0.05)
    let region = MKCoordinateRegionMake(placemark.coordinate, span)
    mapView.setRegion(region, animated: true)
}

}

// Drop Pin amd show route into queried location

extension ViewController : MKMapViewDelegate {

private func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) {

    //Drop Pin
    mapView.delegate = self

    // Convert source and destination routes to latitude and longitude
    let location = locationManager.location
    let sourceLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location!.coordinate.latitude, location!.coordinate.longitude)

    // Make them placemarks (probably a duplicate of above but I dont know how to call the existing policy holder placemark from the two functions)
    let sourcePlacemark = MKPlacemark(coordinate: sourceLocation, addressDictionary: nil)

    // Make them mapitems
    let sourceMapItem = MKMapItem(placemark: sourcePlacemark)
    let destinationMapItem = MKMapItem(placemark: selectedPin!)

    // set up and calculate the route
    let directionRequest = MKDirectionsRequest()
    directionRequest.source = sourceMapItem
    directionRequest.destination = destinationMapItem
    directionRequest.transportType = .automobile

    // Calculate the direction
    let directions = MKDirections(request: directionRequest)

    // Draw the directions (not working!!!)
    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)
    }    }


func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
    let renderer = MKPolylineRenderer(overlay: overlay)
    renderer.strokeColor = UIColor.red
    renderer.lineWidth = 4.0

    return renderer
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
}