按下按钮后Xcode会聚焦用户位置

Question

我正在开发一个小型地图应用程序，我希望一旦用户按下刷新按钮，地图就会将用户当前位置置于屏幕中心。目前我有这个代码，但按下按钮后似乎没有任何事情发生：

import UIKit
import MapKit
import CoreLocation

class ViewController: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate {

var location: CLLocation!
let locationManager = CLLocationManager()

@IBOutlet weak var mapView: MKMapView!
@IBOutlet weak var refresh: UIBarButtonItem!

@IBAction func refresh(sender: AnyObject) {

    let center = CLLocationCoordinate2D(latitude: location.coordinate.latitude, longitude: location.coordinate.longitude)

    let region = MKCoordinateRegion(center: center, span: MKCoordinateSpan(latitudeDelta: 0.01, longitudeDelta: 0.01))

    self.mapView.setRegion(region, animated: true)
}

override func viewDidLoad() {
    super.viewDidLoad()

    self.locationManager.delegate = self

    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest

    self.locationManager.requestWhenInUseAuthorization()

    self.locationManager.startUpdatingLocation()

    self.mapView.showsUserLocation = true

}

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

// location delegate methods

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    let location = locations.last

    let center = CLLocationCoordinate2D(latitude: location!.coordinate.latitude, longitude: location!.coordinate.longitude)

    let region = MKCoordinateRegion(center: center, span: MKCoordinateSpan(latitudeDelta: 1, longitudeDelta: 1))

    self.mapView.setRegion(region, animated: true)

    self.locationManager.stopUpdatingLocation()

}

func locationManager(manager: CLLocationManager, didFailWithError error: NSError)
{
    print("Error code: " + error.localizedDescription)
}

}

我是Swift的新手，所以感谢任何帮助：）

谢谢！