SwiftUI&UIView-ASimpleMistake_CorrectImplementation.swift

import SwiftUI
import MapKit

// Main view
struct ContentView: View {

    // Provides an annotation after some delay (asynchronously)
    @ObservedObject var asynchronousAnnotationMaker = AsynchronousAnnotationMaker()

    var body: some View {
        MapView(annotation: asynchronousAnnotationMaker.annotation).edgesIgnoringSafeArea(.all)
            .onAppear {
                self.asynchronousAnnotationMaker.makeAnnotation()
        }
    }
}

// Map view. Displays a map and a single map annotation.
struct MapView: UIViewRepresentable {

    var annotation: MKAnnotation?

    func makeUIView(context: Context) -> MKMapView {
        return MKMapView()
    }

    func updateUIView(_ mapView: MKMapView, context: Context) {
        refreshAnnotation(onMap: mapView)
    }

    private func refreshAnnotation(onMap mapView: MKMapView) {
        mapView.removeAnnotations(mapView.annotations)
        if let annotation = annotation {
            mapView.addAnnotation(annotation)
        }
    }
}

// Provides a map annotation afte some delay. A timer is used to simulate a delay which may occur due to a network request
class AsynchronousAnnotationMaker: ObservableObject {

    @Published var annotation: MKAnnotation?

    func makeAnnotation() {
        Timer.scheduledTimer(withTimeInterval: 2, repeats: false) { timer in
            self.annotation = MKPlacemark(coordinate: CLLocationCoordinate2D(latitude: 53.345589, longitude: -6.286951), addressDictionary: ["City":"Dublin", "Country":"Ireland"])
        }
    }
}