但是当我尝试导航并显示“MKRoutePolyline”时,这个应用程序崩溃了

interiorPolygons：发送到实例0x14ed4b4d0的无法识别的选择器“

我的代码怎么了？

import UIKit
import MapKit
class MapViewController: UIViewController,MKMapViewDelegate {
var farm:Farm!

var currentPlacemark:CLPlacemark?

let locationManager = CLLocationManager()
var currentTransportType = MKDirectionsTransportType.Automobile
var currentRoute:MKRoute?




@IBOutlet var mapView:MKMapView!
@IBAction func showDirection(sender: AnyObject){
    let directionRequest = MKDirectionsRequest()

    directionRequest.source = MKMapItem.mapItemForCurrentLocation()
    let destinationPlacemark = MKPlacemark(placemark: currentPlacemark!)
    directionRequest.destination = MKMapItem(placemark: destinationPlacemark)
    directionRequest.transportType = currentTransportType

    let directions = MKDirections(request: directionRequest)

    directions.calculateDirectionsWithCompletionHandler { (routeResponse,routeError) -> Void in

        guard let routeResponse = routeResponse else {
            if let routeError = routeError {
                print("Error: \(routeError)")
            }

            return
        }

        let route = routeResponse.routes[0]
        self.currentRoute = route
        self.mapView.removeOverlays(self.mapView.overlays)
        self.mapView.addOverlay(route.polyline,level: MKOverlayLevel.AboveRoads)



    }
}


func mapView(mapView: MKMapView,rendererForOverlay overlay: MKOverlay) -> MKOverlayRenderer {
    let renderer = MKPolygonRenderer(overlay: overlay)
    renderer.strokeColor = UIColor.yellowColor()
    renderer.lineWidth = 3.0

    return renderer

}