在斯威夫特，IBOutlet意外地发现自我代表没有？

Question

这个问题绝对让我感到疯狂，而且我一直在寻找解决方案。请原谅可能是一个基本问题......

我按照教程制作了一个简单的Geofence应用程序。问题是，当我声明它时，我的MKMapView不断给我一个nil变量，在解开一个Optional值时，给了我＆＃34;意外发现的nil＆＃34;错误。

有问题的变量是mapView，而给我一个问题的那一行是mapView.delegate = self

这是我的代码：

import UIKit
import CoreLocation
import MapKit

class ViewController: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate {

    @IBOutlet weak var mapView: MKMapView!

    let locationManager = CLLocationManager()

    override func viewDidLoad() {
        super.viewDidLoad()

        // setup locationManager
        locationManager.delegate = self
        locationManager.distanceFilter = kCLLocationAccuracyNearestTenMeters
        locationManager.desiredAccuracy = kCLLocationAccuracyBest

        // setup mapView
        mapView.delegate = self
        mapView.showsUserLocation = true
        mapView.userTrackingMode = .follow

        // setup test data
        setupData()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        // status is not determined
        if CLLocationManager.authorizationStatus() == .notDetermined {
            locationManager.requestAlwaysAuthorization()
        }
            // authorization were denied
        else if CLLocationManager.authorizationStatus() == .denied {
            showAlert(title: "Location services were previously denied. Please enable location services for this app in Settings.")
        }
            // we do have authorization
        else if CLLocationManager.authorizationStatus() == .authorizedAlways {
            locationManager.startUpdatingLocation()
        }
    }

    func setupData() {
        // check if can monitor regions
        if CLLocationManager.isMonitoringAvailable(for: CLCircularRegion.self) {

            // region data
            let title = "Weber"
            let coordinate = CLLocationCoordinate2DMake(37.703026, -121.759735)
            let regionRadius = 300.0

            // setup region
            let region = CLCircularRegion(center: CLLocationCoordinate2D(latitude: coordinate.latitude, longitude: coordinate.longitude), radius: regionRadius, identifier: title)
            locationManager.startMonitoring(for: region)

            // setup annotation
            let restaurantAnnotation = MKPointAnnotation()
            restaurantAnnotation.coordinate = coordinate;
            restaurantAnnotation.title = "\(title)";
            mapView.addAnnotation(restaurantAnnotation)

            // setup circle
            let circle = MKCircle(center: coordinate, radius: regionRadius)
            mapView.add(circle)
        }
        else {
            print("System can't track regions")
        }
    }

    // MARK: - MKMapViewDelegate
    func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        let circleRenderer = MKCircleRenderer(overlay: overlay)
        circleRenderer.strokeColor = UIColor.blue
        circleRenderer.lineWidth = 1.0
        return circleRenderer
    }

    // MARK: - CLLocationManagerDelegate
    func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {
        showAlert(title: "enter \(region.identifier)")

    }

    func locationManager(_ manager: CLLocationManager, didExitRegion region: CLRegion) {
        showAlert(title: "exit \(region.identifier)")   
    }

    // MARK: - Helpers
    func showAlert(title: String) {
        let alert = UIAlertController(title: title, message: nil, preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "Cancel", style: .default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}