如何在swift中侦听数组更新或其他变量

我是一名android开发者，我开始学习Swift。到目前为止，我想做什么就做什么，但我很难在

SwiftUI

中收听更新

我实现了一个使用

Firestore

从数据库读取数据的服务。此服务是一个

可观察对象

。在服务内部，我有一个变量被注释为

@Published

：

@Published var events = [Event]()

我已经实现了GoogleMaps，我想获取这些事件并对它们进行处理，但我不知道如何在通话结束时进行监听和处理

谷歌地图类：

import SwiftUI
import GoogleMaps

struct GoogleMapsView: UIViewRepresentable {
    
    @ObservedObject var databaseService = DatabaseService()
    
    func makeUIView(context: Self.Context) -> GMSMapView {
        let camera = GMSCameraPosition.camera(withLatitude: 45.764375, longitude: 24.994272, zoom: 6.0)
        let mapView = GMSMapView.map(withFrame: CGRect.zero, camera: camera)
        // Here I think I call .getEvents
        databaseService.getEvents()          
        
        return mapView
    }
    
    func updateUIView(_ mapView: GMSMapView, context: Context) {
        // Listen to events update and update them like this, but I don't know how...

        for event in self.databaseService.events {
            let marker = GMSMarker()
            marker.position = CLLocationCoordinate2D(latitude: event.lat, longitude: event.long)
            marker.title = event.title
            marker.snippet = event.title
            marker.map = mapView
        }
    }
}

struct GoogleMapsView_Previews: PreviewProvider {
    static var previews: some View {
        GoogleMapsView()
    }
}

和我的

SwiftUI

视图：

import SwiftUI

struct CommunicationsView: View {
    
    @ObservedObject var databaseService = DatabaseService()
    
    var body: some View {
        TabView() {
            GoogleMapsView()
                .edgesIgnoringSafeArea(.top)
                .tabItem {
                    Image(systemName: "leaf.fill")
                    Text("Campanii")
            }
        }.accentColor(.green)
    }
}

struct CommunicationsView_Previews: PreviewProvider {
    static var previews: some View {
        CommunicationsView()
    }
}

还有，这是我的服务：

class DatabaseService : ObservableObject {

let db: Firestore
@Published var events = [Event]()

init() {
    db = Firestore.firestore()
}

func getEvents() -> Void {
    var tempoEvents = [Event]()
    db.collection(DatabaseName.CAMPAIGNS.rawValue).getDocuments { (query: QuerySnapshot?, error: Error?) in
        for document in query!.documents {
            let data = document.data()
            let title = data["title"] as? String ?? ""
            let details = data["details"] as? String ?? ""
            let lat = data["lat"] as? Double ?? 0.0
            let long = data["long"] as? Double ?? 0.0
            let date = data["date"] as? Date ?? Date()
            let author = data["author"] as? String ?? ""
            tempoEvents.append(Event(id: document.documentID, title: title, details: details, lat: lat, long: long, date: date, author: author))
        }
        
        self.events.append(contentsOf: tempoEvents)
    }
}
}

你需要把

 @ObservedObject var databaseService = DatabaseService()

仅限内部

通信视图

与

GoogleMapsView(events:self.databaseService.events)

并在

GoogleMapsView

struct GoogleMapsView: UIViewRepresentable {
  var events = [Event]()
  ......
  for event in self.events {
  }
}

最后在

数据库服务的
init
中

init() {
   db = Firestore.firestore()
   self.getEvents()
}

但是我什么时候调用databaseService.getEvents？我应该使用像.onAppear这样的东西吗？这也是另一种方法，或者在
init
中。在我的情况下，映射是在服务完成抓取之前呈现的，我应该怎么做？您无需做这就是异步进程的运行方式-如果需要，您可以显示加载