I’m making a test app that is taking in geological points of interest from a JSON file and plotting the points on a map (you can see the info I am getting here: https://maine.hub.arcgis.com/datasets/ff3e487fb782464684f8c1f8a1b7e58d_0/about and you can see the JSON file there as well). I’ve been trying to color-code the points to correspond to the category of geological feature (bedrock is red, coastal is green, surficial is purple, etc.). However, when I try to apply the colors, it doesn’t work. The app runs just fine, and I can see all the points, they’re just not color-coded or labeled as their object ID.

This is the file I used for each item (titled Artwork because this project was previously locations of artworks in Oahu, but changed to geological formations in Maine):

import Foundation
import MapKit
import Contacts
import SwiftUI

class Artwork: NSObject, MKAnnotation {
    let title: String?
    let locationName: String?
    let type: String?
    let coordinate: CLLocationCoordinate2D
    let objectID: Int?
    
    init(title: String?, locationName: String?, type: String?, coordinate: CLLocationCoordinate2D, objectID: Int?) {
        self.title = title
        self.locationName = locationName
        self.type = type
        self.coordinate = coordinate
        self.objectID = objectID
        
        super.init()
    }
    
    init?(feature: MKGeoJSONFeature) {
        guard
            let point = feature.geometry.first as? MKPointAnnotation,
            let propertiesData = feature.properties,
            let json = try? JSONSerialization.jsonObject(with: propertiesData),
            let properties = json as? [String: Any]
        else {
            return nil
        }
        
        title = properties["SITE_NAME"] as? String
        locationName = properties["TOWN"] as? String
        type = properties["CATEGORY"] as? String
        coordinate = point.coordinate
        objectID = properties["OBJECTID"] as? Int
        super.init()
    }
    
    var subtitle: String? {
        return locationName
    }
    
    var mapItem: MKMapItem? {
        guard let location = locationName else {
            return nil
        }
        
        let addressDict = [CNPostalAddressStreetKey: location]
        let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDict)
        let mapItem = MKMapItem(placemark: placemark)
        mapItem.name = title
        return mapItem
    }
    
    //This is where I code the method for choosing the color
    var markerTintColor: UIColor {
        switch type {
        case "Bedrock":
            return .red
        case "Coastal":
            return .green
        case "Surficial":
            return .purple
        case "Bedrock, Surficial":
            return .blue
        case "Bedrock, Surficial, Coastal":
            return .cyan
        case "Surficial, Coastal":
            return .magenta
        case "Bedrock, Coastal":
            return .orange
        default:
            return .gray
        }
    }
}

Here is another file that might be important, ArtworkViews.swift:

import Foundation
import MapKit
import SwiftUI

class ArtworkViews: MKMarkerAnnotationView {
    override var annotation: MKAnnotation? {
        willSet {
            guard let artwork = newValue as? Artwork else {
                return
            }
            canShowCallout = true
            calloutOffset = CGPoint(x: -5, y: 5)
            rightCalloutAccessoryView = UIButton(type: .detailDisclosure)
            
            //This is where the color and ID are applied
            markerTintColor = artwork.markerTintColor
            if let ID = artwork.objectID {
                glyphText = String(ID)
            }
        }
    }
}

And here is where I implement the colors in ViewController.swift (this the viewDidLoad() function):

let initialLocation = CLLocation(latitude: 44.883427, longitude: -68.670815)
        
mapView.centerToLocation(initialLocation)
        
let maineCenter = CLLocation(latitude: 44.883427, longitude: -68.670815)
let region = MKCoordinateRegion(center: maineCenter.coordinate, latitudinalMeters: 600000, longitudinalMeters: 300000)
mapView.setCameraBoundary(MKMapView.CameraBoundary(coordinateRegion: region), animated: true)
        
let zoomRange = MKMapView.CameraZoomRange(maxCenterCoordinateDistance: 1400000)
mapView.setCameraZoomRange(zoomRange, animated: true)
        
mapView.delegate = self

//This is where the color is ultimately applied        
mapView.register(ArtworkViews.self, forAnnotationViewWithReuseIdentifier: MKMapViewDefaultAnnotationViewReuseIdentifier)
        
loadInitialData()
mapView.addAnnotations(artworks)