mapView.addAnnotation（）表示“在展开Optional值时意外发现nil”

我尝试从tableView单元格的地址转换为mapView并在 Map 上显示引脚 .

我确信我的代码中的所有内容都不是零 .

但是Xcode说我的 oldValue 是 nil （在 didSet{} 中） . 我不知道如何解决它 .

以下是我的代码：

class MapViewController: UIViewController, MKMapViewDelegate {

    @IBOutlet weak var mapView: MKMapView! {
        didSet {
            mapView.mapType = .Standard
            mapView.delegate = self
        }
    }


    var location:CLLocation? {
        didSet {
            clearWayPoints()
            if location != nil {
                println(location!.coordinate.longitude)
                let coordinate = CLLocationCoordinate2D(latitude: location!.coordinate.latitude, longitude: location!.coordinate.longitude)
                let pin = MapPin(coordinate: coordinate, title: "Current", subtitle: "here")
                setAnnotation(pin)
            }
        }
    }

    private func clearWayPoints() {
        if mapView?.annotations != nil {
            mapView.removeAnnotations(mapView.annotations as [MKAnnotation])
        }
    }

    func setAnnotation(pin: MKAnnotation) {        
        mapView.addAnnotation(pin)
        mapView.showAnnotations([pin], animated: true)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    func mapView(mapView: MKMapView!, viewForAnnotation annotation: MKAnnotation!) -> MKAnnotationView! {
        var view = mapView.dequeueReusableAnnotationViewWithIdentifier(Constants.AnnotationViewReuseIdentifier)
        if view == nil {
            view = MKPinAnnotationView(annotation: annotation, reuseIdentifier: Constants.AnnotationViewReuseIdentifier)
            view.canShowCallout = true
        } else {
            view.annotation = annotation
        }
        return view

    }

    struct Constants {
        static let AnnotationViewReuseIdentifier = "map cell"
    }
}

我的模型只是 var location:CLLocation? ，我从我的segue更新了这个值 .

我确信我在println（）中得到了正确的坐标 .

但Xcode总是说

致命错误：在展开Optional值时意外发现nil

我发现 nil 似乎是 oldValue=(CLLocation?)nil ！

以下是我的简单类 MapPin ，它实现 MKAnnotation

class MapPin: NSObject, MKAnnotation {
    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?

    init(coordinate: CLLocationCoordinate2D, title: String, subtitle: String) {
        self.coordinate = coordinate
        self.title = title
        self.subtitle = subtitle
    }
}