UIViewRepresentable - MKMapView 没有得到更新

Question

I'm dealing with an app where I have to embed a MKMapView (UIKit) into a SwiftUI View. Unfortunately I can't use the implemented Map of SwiftUI, because I have to support clustering (which Map can't do at the moment).
The problem is, that the MKMapView doesn't reflect changes applied to the data source ( persons array).

ContentView

struct ContentView: View {
    @State private var persons: [Person] = [
        .init(
            coordinate: .init(latitude: 50.7123012, longitude: 5.1231021),
            title: "Person 1"
        ),
        .init(
            coordinate: .init(latitude: 49.3123012, longitude: 5.1231021),
            title: "Person 2"
        )
    ]
    
    var body: some View {
        VStack {
            MapView(persons: $persons)
            Button("Remove Person at index 0") {
                persons.remove(at: 0)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Implementation of MKMapView with the help of UIViewRepresentable :

struct MapView: UIViewRepresentable {
    @Binding var persons: [Person]
    private let mapView = MKMapView()
    
    init(persons: Binding<[Person]>) {
        self._persons = persons
        // other stuff
    }
    
    func makeUIView(context: Context) -> MKMapView {
        mapView.delegate = context.coordinator
        mapView.register(MKMarkerAnnotationView.self, forAnnotationViewWithReuseIdentifier: "testAnnotation")
        return mapView
    }
    
    func updateUIView(_ uiView: MKMapView, context: Context) {
        DispatchQueue.main.async {
            mapView.removeAnnotations(mapView.annotations)
            mapView.addAnnotations(persons)
        }
    }
}

extension MapView {
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject, MKMapViewDelegate {
        
        var parent: MapView
        
        init(_ parent: MapView) {
            self.parent = parent
        }

        func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
            if let annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: "testAnnotation", for: annotation) as? MKMarkerAnnotationView {
                annotationView.glyphImage = UIImage(systemName: "person")
                return annotationView
            }
            
            return nil
        }
    }
}

Demo Model:

class Person: NSObject, MKAnnotation {
    var coordinate: CLLocationCoordinate2D
    let title: String?
    
    init(coordinate: CLLocationCoordinate2D, title: String?) {
        self.coordinate = coordinate
        self.title = title
    }
}

Please note, that this is a simplified implementation where I removed logic for clustering, etc. to focus on the problem.

---

If you tap on "Remove Person at index 0" it actually removes the entry at index 0 but unfortunately the map isn't updated. The problem is that updateUIView in MapView doesn't get called and I'm not sure, why this is the case.
Thanks for your help :-)...

Answer 1

Two issues create map view inside makeView - that's a place for that by design, update annotations right in update (no delay needed) it is a place called on binding update exactly to update UIView counterpart (all UI invalidation/refreshing is made automatically)

So, here is fixed version. Tested with Xcode 13.4 / iOS 15.5

struct MapView: UIViewRepresentable {
    @Binding var persons: [Person]

    init(persons: Binding<[Person]>) {
        self._persons = persons
        // other stuff
    }

    func makeUIView(context: Context) -> MKMapView {

        let mapView = MKMapView()      // << here !!

        mapView.delegate = context.coordinator
        mapView.register(MKMarkerAnnotationView.self, forAnnotationViewWithReuseIdentifier: "testAnnotation")
        return mapView
    }

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

        mapView.removeAnnotations(mapView.annotations)    // << here !!
        mapView.addAnnotations(persons)

    }
}