Altering Existing MKOverlays - How to identify which to alter? - swift

Question

I am trying to change the color of an existing MKOverlay on a map.
I am add several MKPolygons as unique overlays to mapView. As they are rendered, the overlay's color is applied by the mapView rendererFor function.
Periodically I would like to change the color of an existing overlay; ideally without removingAll and re-adding. I have code that will handle the color change, but I do not know how to identify different overlays other than by their type (MKPolygon, MKCircle) - but all overlays in my situation are MKPolygon, so executing the code simply changes all.
I have tried converting the MKPolygon into an MKOverlay before using addOverlay and manipulating the title, but title is "get-only"
I have tried subclassing MKPolygon, but my reading says this is bad in Swift.
I add the overlay like this.
var shapeNW:MKMapPoint = MKMapPoint( CLLocationCoordinate2D(latitude: 48.313319, longitude: -124.109715))
var shapeNE:MKMapPoint = MKMapPoint( CLLocationCoordinate2D(latitude: 48.313312, longitude: -124.108695))
var shapeSW:MKMapPoint = MKMapPoint( CLLocationCoordinate2D(latitude: 48.312661, longitude: -124.109767))
var shapeSE:MKMapPoint = MKMapPoint( CLLocationCoordinate2D(latitude: 48.312626, longitude: -124.108679))
var myShapePoints:[MKMapPoint] = [shapeNW,shapeNE,shapeSE,shapeSW]
// addAnItemToMap(title: "Circle", locationName: "CircleName", type: "SS", coordinate: feiLocation, horizontalAccuracy: 20)
var myShape:MKPolygon = MKPolygon(points: myShapePoints, count: 4)
mapView.addOverlay(myShape)
Here is my function that I use to change the color after it is created. But obviously this function changes the color of all items as it cannot identify which overlay to change. This is my issue, I would like to identify the specific overlay and change just it.
func changeColor(identifier: String) {
let overlays = self.mapView.overlays
let duration:TimeInterval = 5.0
for overlay in overlays {
if identifier == "on"{
let renderer = mapView.renderer(for: overlay) as! MKPolygonRenderer
DispatchQueue.main.async{
renderer.alpha = 1.0
renderer.fillColor = UIColor.blue
}
}
else {
let renderer = mapView.renderer(for: overlay) as! MKPolygonRenderer
DispatchQueue.main.async{
renderer.alpha = 0.0
}
}
}
}

Answer 1

You can just subclass MKPolygon:
class CustomPolygon: MKPolygon {
var identifier: String? = nil
}
Then you can configure your renderer accordingly:
func configureColor(of renderer: MKPolygonRenderer, for overlay: MKOverlay) {
let baseColor: UIColor
if let polygon = overlay as? CustomPolygon, polygon.identifier == "on" {
baseColor = .cyan
} else {
baseColor = .red
}
renderer.strokeColor = baseColor.withAlphaComponent(0.75)
renderer.fillColor = baseColor.withAlphaComponent(0.25)
}
Then your main renderer(for:) can use that:
extension ViewController: MKMapViewDelegate {
func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
let renderer = MKPolygonRenderer(overlay: overlay)
renderer.lineWidth = 5
configureColor(of: renderer, for: overlay)
return renderer
}
}
As can your update routine can:
func updateColors() {
for overlay in mapView.overlays {
if let renderer = mapView.renderer(for: overlay) as? MKPolygonRenderer {
configureColor(of: renderer, for: overlay)
}
}
}
Personally, rather than having overlays whose identifier is not "on" have an alpha of 0, I just would remove those overlays from the map, and then you don’t have to deal with any of this.