Trying to assign to an @EnvironmentObject from a child view to a parent fails as EnvironmentObject is read-only

Question

I have a map based app so I want to have an app-wide property for the current position of the map.

I'm initializing it in SceneDelegate

    let currentPosition = CurrentPosition()
    let mainView = MainView(appState: AppState(), selectedWeatherStation: nil).environmentObject(currentPosition)

I have it declared in MainView as an @EnvironmentObject

struct MainView: View {
    @State var appState: AppState
    @State var selectedWeatherStation: WeatherStation? = nil

    @EnvironmentObject var currentPosition: CurrentPosition

and I inject it into my UIViewRepresentable child

 MapView(weatherStations: $appState.appData.weatherStations,
                    selectedWeatherStation: $selectedWeatherStation).environmentObject(currentPosition)
                    .edgesIgnoringSafeArea(.vertical)

in MapView

struct MapView: UIViewRepresentable {
    @Binding var weatherStations: [WeatherStation]
    @Binding var selectedWeatherStation: WeatherStation?

    @EnvironmentObject var currentPosition: CurrentPosition

i have a final subclass

final class Coordinator: NSObject, MKMapViewDelegate {
        @EnvironmentObject var currentPosition: CurrentPosition

which acts as my mapview delegate, where I want to update the currentPosition

  func mapViewDidChangeVisibleRegion(_ mapView: MKMapView) {
            currentPosition = CurrentPosition(northEast: mapView.northEastCoordinate, southWest: mapView.southWestCoordinate)
        }

But this assignament currentPosition = CurrentPosition(northEast: mapView.northEastCoordinate, southWest: mapView.southWestCoordinate) will throw an error Cannot assign to property: 'currentPosition' is a get-only property and I really have no idead what I'm doing wrong.

The purpose is to update the position each time the user moves the map so I can perform a request to my API with the current coordinates.

CurrentPosition is declared as follows

class CurrentPosition: ObservableObject {
    @Published var northEast = CLLocationCoordinate2D()
    @Published var southWest = CLLocationCoordinate2D()

    init(northEast: CLLocationCoordinate2D = CLLocationCoordinate2D(), southWest: CLLocationCoordinate2D = CLLocationCoordinate2D()) {
        self.northEast = northEast
        self.southWest = southWest
    }
}

You just change the properties of the class, rather than trying to make another class. Like so: `currentPosition.northEast = mapView.northEastCoordinate`. — George, Feb 08 '20 at 23:50

George · Accepted Answer · 2020-02-09T11:53:10.243

1

Full answer (extended from comment)

You just change the properties of the class, rather than trying to make another class. Like so:

func mapViewDidChangeVisibleRegion(_ mapView: MKMapView) {
    currentPosition.northEast = mapView.northEastCoordinate
    currentPosition.southWest = mapView.southWestCoordinate
}

The error:

Cannot assign to property: 'currentPosition' is a get-only property

is saying that you cannot assign a value directly to currentPosition, because it is an @ObservedObject/@EnvironmentObject. It is only a gettable property.

edited Feb 09 '20 at 11:53

answered Feb 09 '20 at 11:47

George

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how do u make an @environmentObject not a get-only property? – ngb Nov 17 '21 at 09:39
@ngb It doesn't really make sense to do that. `@EnvironmentObject` detects changes for an _instance_ of a class, which is why my solution changes a property of the class instead. – George Nov 17 '21 at 09:50

Trying to assign to an @EnvironmentObject from a child view to a parent fails as EnvironmentObject is read-only

1 Answers1