MapKit Annotations Disappearing

Question

I have an array of latitudes and another array of longitudes that I add to an array of type CLLocationCoordinate2D. I then use the new array to annotate multiple points on the map. Some, or most, or maybe even all of the annotations are displaying on the map but as I zoom in (yes, zoom IN), some of the annotations disappear, then come back, or dont. Any ideas on how to keep them all visible? This is behavior I would expect while zooming out, not in.

Here is the code i'm using for what i've described above.

import UIKit
import MapKit
import CoreLocation

class MultiMapVC: UIViewController, CLLocationManagerDelegate {

@IBOutlet weak var multiEventMap: MKMapView!

var latDouble = Double()
var longDouble = Double()
let manager = CLLocationManager()
var receivedArrayOfLats = [Double]()
var receivedArrayOfLongs = [Double]()
var locations = [CLLocationCoordinate2D]()


func locationManager(_ manager: CLLocationManager, didUpdateLocations uLocation: [CLLocation]) {
    let userLocation = uLocation[0]
    let span:MKCoordinateSpan = MKCoordinateSpanMake(0.3, 0.3)
    let usersLocation = userLocation.coordinate
    let region:MKCoordinateRegion = MKCoordinateRegionMake(usersLocation, span)
    multiEventMap.setRegion(region, animated: true)
    manager.distanceFilter = 1000
    self.multiEventMap.showsUserLocation = true
}

func multiPoint() {

    var coordinateArray: [CLLocationCoordinate2D] = []
    print ("Received Longitude Count = \(receivedArrayOfLongs.count)")
    print ("Received Latitude Count = \(receivedArrayOfLats.count)")
    if receivedArrayOfLats.count == receivedArrayOfLongs.count {
        for i in 0 ..< receivedArrayOfLats.count {
            let eventLocation = CLLocationCoordinate2DMake(receivedArrayOfLats[i], receivedArrayOfLongs[i])
            coordinateArray.append(eventLocation)
            print (coordinateArray.count)
        }
    }

    for events in coordinateArray {
        let annotation = MKPointAnnotation()
        annotation.coordinate = CLLocationCoordinate2D(latitude: events.latitude, longitude: events.longitude)
        multiEventMap.addAnnotation(annotation)
        }
}


override func viewDidLoad() {
    super.viewDidLoad()
    manager.delegate = self
    manager.desiredAccuracy = kCLLocationAccuracyBest
    manager.requestWhenInUseAuthorization()
    manager.startUpdatingLocation()
    multiPoint()
        }


override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    multiEventMap.removeFromSuperview()
    self.multiEventMap = nil

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

Answer 1

I was setting annotationView.displayPriority = .required only when the MKMarkAnnotationView was first allocated. Normally thats all you should need to do, but setting it each time the cell was reused fixed the issue for me.

Answer 2

NiltiakSivad's solution works but it reverts to the old iOS 10 look. If you want to keep the new iOS 11 balloon markers for iOS 11 and use the old pin look only for older iOS versions then you can implement the delegate method as below:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    let reuseIdentifier = "annotationView"
    var view = mapView.dequeueReusableAnnotationView(withIdentifier: reuseIdentifier)
    if #available(iOS 11.0, *) {
        if view == nil {
            view = MKMarkerAnnotationView(annotation: annotation, reuseIdentifier: reuseIdentifier)
        }
        view?.displayPriority = .required
    } else {
        if view == nil {
            view = MKPinAnnotationView(annotation: annotation, reuseIdentifier: reuseIdentifier)
        }
    }
    view?.annotation = annotation
    view?.canShowCallout = true
    return view
}

Answer 3

The accepted answer from Leszek Szary is correct.

But there is some fineprint. Sometimes MKMarkerAnnotationViews are not rendered, even if

view.displayPriority = .required

is set.

What you are seeing is a combination of different rules.

1. MKAnnotationViews are rendered from top to bottom of the map. (It doesn't matter where north is).
2. If MapKit decides to draw overlapping MKAnnotationViews, then the MKAnnotationView nearer to the bottom is drawn on top (because it's drawn later)
3. Not only MKAnnotationViews, also titles rendered below MKMArkerAnnotationViews need space. The rendering of those titles is influenced by markerView.titleVisibility. If markerView.titleVisibility is set to .visible (instead of the default .adaptive), then this title is stronger than a MarkerAnnotationView that is rendered later, even if the later MarkerAnnotationView has a displayPriority = .required. The MarkerAnnotationView nearer to the bottom is not rendered.
4. This even happens if the MarkerAnnotationView nearer to the top has a low displayPriority. So a MarkerAnnotationView with low displayPriority and .titleVisibility = .visible can make a MarkerAnnotationView nearer to the bottom with displayPriority = .required disappear.

I am not aware of a documentation of this behaviour. This is the result of my experiments with iOS 12. My description is sipmplified.