路线未显示在MKMapView中？

实际上，源变量和目标变量都为nil。因此，我从server。如果收到错误响应，请尝试以下代码

func addRoutesOverLayForMapView(){    var source:MKMapItem?    var destination:MKMapItem?    var sourcePlacemark = MKPlacemark(coordinate: pickUpDistanceLocation!.coordinate, addressDictionary: nil)    source = MKMapItem(placemark: sourcePlacemark)    var desitnationPlacemark = MKPlacemark(coordinate: dropOffDistanceLocation!.coordinate, addressDictionary: nil)    destination = MKMapItem(placemark: desitnationPlacemark)    let request:MKDirectionsRequest = MKDirectionsRequest()    request.setSource(source)    request.setDestination(destination)    request.transportType = MKDirectionsTransportType.Walking    let directions = MKDirections(request: request)    directions.calculateDirectionsWithCompletionHandler ({        (response: MKDirectionsResponse?, error: NSError?) in        if error == nil { self.showRoute(response!)        }        else{        println("trace the error (error?.localizedDescription)")        }    }) }func showRoute(response:MKDirectionsResponse){    for route in response.routes as! [MKRoute]{        mapView.addOverlay(route.polyline, level: MKOverlayLevel.AboveRoads)        var routeSeconds = route.expectedTravelTime        let routeDistance = route.distance        println("distance between two points is (routeSeconds) and (routeDistance)")    }}

而且您应该实现此委托方法，不要忘记设置mapview委托

  func mapView(mapView: MKMapView!, rendererForOverlay overlay: MKOverlay!) -> MKOverlayRenderer! {        if overlay is MKPolyline { var polylineRenderer = MKPolylineRenderer(overlay: overlay) polylineRenderer.lineDashPattern = [14,10,6,10,4,10] polylineRenderer.strokeColor = UIColor(red: 0.012, green: 0.012, blue: 0.012, alpha: 1.00) polylineRenderer.lineWidth = 2.5 return polylineRenderer        }        return nil    }