SwiftUI Map: setting userTrackingMode causes console warning

Number:rdar://FB9990674 Date Originated:2022-04-22
Status:Open Resolved:No
Product:SwiftUI Product Version:
Classification:Bug Reproducible:Always
Hi I noticed in the SwiftUI map when it is used with coordinateRegion binding and userTracking binding, e.g.

 Map(coordinateRegion: $region, interactionModes: .all, showsUserLocation: true, userTrackingMode: $tracking)

When a button is used to set the userTrackingMode, SwiftUI attempts to update the MKMapView calling [MKMapView _setUserTrackingMode:...] which results in mapLayerDidChangeVisibleRegion which unfortunately results in it setting the coordinateRegion binding. Of course we aren't supposed to update state when SwiftUI is trying to update the view, and it results in the the warning output to console:

[SwiftUI] Modifying state during view update, this will cause undefined behavior.

Hope this can be fixed!

I discovered this when I answered this Stackoverflow question


Xcode Version 13.3.1 (13E500a)
iPhone 13 simulator

Here is a View you can use

struct MapTestView: View {
    @State var region: MKCoordinateRegion = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: 47.3769, longitude: 8.5417), latitudinalMeters: 2000, longitudinalMeters: 2000)
    @State var tracking = MapUserTrackingMode.follow
    var body: some View {
        let _ = Self._printChanges()
        VStack {
            Map(coordinateRegion: $region, interactionModes: .all, showsUserLocation: true, userTrackingMode: $tracking)
                .task {
                    let locationManager = CLLocationManager()
            Button {
                tracking = .follow
            } label: {
                Image(systemName: tracking == .follow ? "location.fill" : "location")


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