MapKit clustering doesn't cluster properly at start, it clusters after panning - swift

Question

I have a problem with clustering in MapKit, it doesn't work properly at start, I have to pan some time to force MapKit to "recalculate" clustering. The video below shows the problem.
https://youtu.be/5PK7uAV0F_8
My code's description
I have a class class MapKitViewController: UIViewController, MKMapViewDelegate with methods
override func loadView() {
super.loadView()
mapView = MKMapView(frame: view.bounds)
mapView.delegate = self
view.addSubview(mapView)
mapView.translatesAutoresizingMaskIntoConstraints = false
mapView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
mapView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
mapView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
mapView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
}
private func registerAnnotationViewClasses() {
mapView.register(MKMarkerAnnotationView.self, forAnnotationViewWithReuseIdentifier: MKMapViewDefaultAnnotationViewReuseIdentifier)
mapView.register(ClusterAnnotationView.self, forAnnotationViewWithReuseIdentifier: MKMapViewDefaultClusterAnnotationViewReuseIdentifier)
}
override func viewDidLoad() {
super.viewDidLoad()
registerAnnotationViewClasses()
}
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
if annotation is MyAnnotation {
let v = MKMarkerAnnotationView(annotation: annotation, reuseIdentifier: MKMapViewDefaultAnnotationViewReuseIdentifier)
v.titleVisibility = .hidden
v.clusteringIdentifier = "clusterID"
return v
} else {
return nil
}
}
And this is my cluster annotation view class
class ClusterAnnotationView: MKAnnotationView {
override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
setUp()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUp()
}
private func setUp() {
collisionMode = .circle
}
override func prepareForDisplay() {
super.prepareForDisplay()
displayPriority = .defaultHigh
if let clusterAnnotation = annotation as? MKClusterAnnotation {
image = image(forMembersCount: clusterAnnotation.memberAnnotations.count)
}
}
private func image(forMembersCount membersCount: Int) -> UIImage {
let size = /* calculate size */
let renderer = UIGraphicsImageRenderer(size: size)
return renderer.image { _ in
/* draw an image */
}
}
}
What can I do to fix this issue?

Answer 1

in
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
if annotation is MyAnnotation {
let v = MKMarkerAnnotationView(annotation: annotation, reuseIdentifier: MKMapViewDefaultAnnotationViewReuseIdentifier)
v.titleVisibility = .hidden
v.clusteringIdentifier = "clusterID"
return v
} else {
return nil
}
}
you are recreating all annotationViews, probably each time you are panning.
These are intended to be reused instead of recreated each time.
So mapView thinks you are replacing your annotationViews with new objects (that's what you are actually doing). This means there can't be a smooth transition of existing views - the old views don't exist any more.
See https://www.raywenderlich.com/7738344-mapkit-tutorial-getting-started#toc-anchor-009
after the title "Configuring the Annotation View"
on how to reuse annotationViews.