swift - 更新用http加载的注释

Question

我正在从我的服务器加载一些地理数据并希望显示它们并抛出注释:

Alamofire.request("http://localhost:1234/app/data").responseJSON { response in
    switch response.result {
    case .success(let value):
        let json = JSON(value)
        var annotations = [Station]()
        for (key, subJson):(String, JSON) in json {
            let lat: CLLocationDegrees = subJson["latitude"].double! as CLLocationDegrees
            let long: CLLocationDegrees = subJson["longtitude"].double! as CLLocationDegrees
            self.annotations += [Station(name: "test", lat: lat, long: long)]
        }

        DispatchQueue.main.async {
            let allAnnotations = self.mapView.annotations
            self.mapView.removeAnnotations(allAnnotations)
            self.mapView.addAnnotations(annotations)
        }

    case .failure(let error):
        print(error)
    }
}

和我的Station类(class):

class Station: NSObject, MKAnnotation {
    var identifier = "test"
    var title: String?
    var coordinate: CLLocationCoordinate2D

    init(name:String, lat:CLLocationDegrees, long:CLLocationDegrees) {
        title = name
        coordinate = CLLocationCoordinate2DMake(lat, long)
    }
}

所以我所做的基本上是:

从远程服务加载数据并将这些数据作为注释显示在 MKMapView 上。

但是:不知何故，这些注释没有加载到 map 上，即使我先“删除”然后再“添加”它们。

有什么建议吗？

Answer 1

您要将 Station 实例添加到某些 self.annotations 属性，而不是本地变量 annotations。因此，annotations local var 仍然只是那个空数组。

显然，您可以通过引用annotations而不是self.annotations来解决这个问题:

var annotations = [Station]()
for (key, subJson): (String, JSON) in json {
    let lat = ...
    let long = ...
    annotations += [Station(name: "test", lat: lat, long: long)] // not `self.annotations`
}

或者您可以使用map，完全避免这种潜在的困惑:

let annotations = json.map { key, subJson -> Station in
    Station(name: "test", lat: subJson["latitude"].double!, long: subJson["longitude"].double!)
}