如何将自定义属性从 Mapbox 注释传递到其标注视图？

Question

我将MGLAnnotation 子类化以添加额外的属性var tags，如下所示：

class MasterMapAnnotation: NSObject, MGLAnnotation {

    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?
    var tags: String?

    init(coordinate: CLLocationCoordinate2D, title: String?, subtitle: String?, tags: String?) {

        self.coordinate = coordinate
        self.title = title
        self.subtitle = subtitle
        self.tags = tags

    }

}

这是传递到地图中的注释：

let annotation = MasterMapAnnotation(coordinate: CLLocationCoordinate2D(latitude: 50.0, longitude: 50.0), title: "Numero Uno", subtitle: "Numero Uno subtitle", tags: "#tag1 #tag2")
mapView.addAnnotation(annotation)

mapView 委托调用自定义标注视图：

func mapView(_ mapView: MGLMapView, calloutViewFor annotation: MGLAnnotation) -> MGLCalloutView? {

    return MasterMapCalloutView(representedObject: annotation)

}

那么在标注视图子类（下）中，我如何访问这个新属性tags？

class MasterMapCalloutView: UIView, MGLCalloutView {

    var representedObject: MGLAnnotation
    let dismissesAutomatically: Bool = false
    let isAnchoredToAnnotation: Bool = true
    lazy var leftAccessoryView = UIView()
    lazy var rightAccessoryView = UIView()
    weak var delegate: MGLCalloutViewDelegate?

    required init(representedObject: MGLAnnotation) {
        self.representedObject = representedObject
        super.init(frame: .zero)
    }

    required init?(coder decoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // callout view delegate: present callout
    func presentCallout(from rect: CGRect, in view: UIView, constrainedTo constrainedView: UIView, animated: Bool) {

        if !representedObject.responds(to: #selector(getter: MGLAnnotation.title)) {
            return
        }

        view.addSubview(self)

        let title = representedObject.title
        let tags = representedObject.tags // how to access this?

    }

}

问题显然是子类（MasterMapAnnotation）拥有自定义tags属性，而不是它的超类（MGLAnnotation），但我不知道如何（a）将representedObject设置为MasterMapAnnotation或（b ) 只需访问MasterMapAnnotation 自定义属性，无需重新配置协议。

Answer 1

我可能遗漏了一些东西，但您肯定只需检查是否可以将 MGLAnnotation 对象转换为 MasterMapAnnotation：

guard let masterAnnotation : MasterMapAnnotation = representedObject as? MasterMapAnnotation else { return }

let tags : String? = masterAnnotation.tags

// etc

显然，除了使用守卫之外，还有其他控制流程的方法，但我希望你明白要点。