Swift - MapView duplicate annotations

Question

I'm querying data from FireStore and displaying the elements on a MapView, using a cursor I am able to paginate data.

This is my custom Annotation class:

final class PostAnnotation: NSObject, MKAnnotation {
    var title: String?
    var coordinate: CLLocationCoordinate2D
    var username: String
    var post: PostModel
    var subtitle: String?
    init(address: PostPlaceMark) {
        self.title = address.title
        self.coordinate = address.coordinate
        self.username = address.username
        self.post = address.post
        self.subtitle = address.subTitle
    }
}

I hit a button to load more data, for testing purposes my data pool is quite small around 7-10 elements. However, whenever I fetch/refresh data, I always get a duplicate of the previous group of annotations.

For instance, when my MapView first loads I have batch of annotations, hit my refresh button I have batch of annotations 1 and batch of annotations 2 but also have a duplicate of batch of annotations 1. Hit refresh again I have batch of annotations one x 3, batch of annotations two x 2 and just one instance of all data belonging to batch of annotations three.

I have managed to figure out where the issue lies but I have two extremes here:

• One I keep getting duplicate annotations
• Two the previous batch is removed

The reason I am doing this is to combat the fact there may/can be a number of annotations surrounding a particular view. I have limited to where the issue and potential solution may lie.

   private static func annotationsByDistributingAnnotationsContestingACoordinate(annotations: [PostAnnotation], constructNewAnnotationWithClosure ctor: annotationRelocator) -> [PostAnnotation] { 
        var newAnnotations = [PostAnnotation]()
        let contestedCoordinates = annotations.map{ $0.coordinate } 
        let newCoordinates = coordinatesByDistributingCoordinates(coordinates: contestedCoordinates)
        newAnnotations.removeAll()
        for (i, annotation) in annotations.enumerated() {
            let newCoordinate = newCoordinates[i]
            let newPost = annotation.post
            let newAnnotation = ctor(annotation, newCoordinate, newPost)
            print(newAnnotation.post.location)
            newAnnotations.forEach { (naac) in
                annotations.forEach { (element) in
                if newAnnotations.contains(where: {$0.post.postID == naac.post.postID}) {
                    let index = newAnnotations.firstIndex{$0.post.postID == naac.post.postID}
                  // newAnnotations.remove(at: index!)
                    print("removed")
                   // newAnnotations.removeAll(where: {$0.post.postID == naac.post.postID})
                }
                }
            }
            newAnnotations.append(newAnnotation)
        }
        let withoutDuplicates = Array(Set(newAnnotations))
        return withoutDuplicates
    }

I can detect if the element is already in the array, however, removing it, even the firstIndex causes me to lose the annotation completely.

This is how I add/update my annotations, in case you was wondering:

private func updateAnnotations(from mapView: MKMapView) {
    let annotations = self.address.map(PostAnnotation.init)

    
    let newAnnotations = ContestedAnnotationTool.annotationsByDistributingAnnotations(annotations: annotations) {
        (oldAnn: MKAnnotation,  newCoordinate:CLLocationCoordinate2D, post: PostModel) -> (PostAnnotation) in
        PostAnnotation(address: PostPlaceMark.init(post: post, coordinate: newCoordinate, title: "\(post.manufacturer) \(post.model)", username: post.username, subTitle: "£\(post.price)"))
    }
    
    mapView.removeAnnotations(mapView.annotations)
    mapView.addAnnotations(newAnnotations)
}