Custom MKAnnotationView - UIImage does not appear

Question

tmsm1999 OP

Created Oct ’20

Replies 1

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Views 3.5k

Participants 2

Hello everybody,

I am trying to create a custom annotation for a map view. Everything works perfectly, except for the UIImage I am trying to show that does not appear.

I think I am not being able to show the MKAnnotationView I am trying to set.

In the mapView method I am not being able to perform that print statement. I can't figure out why.

Code Block import SwiftUI
import UIKit
import MapKit
class ObservationAnnotation: NSObject, MKAnnotation {
    
    let coordinate: CLLocationCoordinate2D
    let title: String?
    let subtitle: String?
    var image: UIImage?
    
    init(coordinate: CLLocationCoordinate2D, species: String, image: UIImage, confidence: Double) {
        self.coordinate = coordinate
        self.title = species
        self.subtitle = "Confidence: \(confidence)"
        self.image = image
    }
}
class ObservationAnnotationView: MKAnnotationView {
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
        guard
            let observationAnnotation = self.annotation as? ObservationAnnotation else {
            return
        }
        
        image = observationAnnotation.image
    }
}
struct MyObservationsMap: UIViewRepresentable {
    
    var observationList: [Observation]
    
    func makeUIView(context: Context) -> MKMapView {
        MKMapView.init(frame: .zero)
    }
    
    func updateUIView(_ uiView: MKMapView, context: Context) {
        
        for observation in observationList {
            
            let annotation = ObservationAnnotation(
                coordinate: CLLocationCoordinate2D(latitude: observation.latitude, longitude: observation.longitude),
                species: observation.speciesName!,
                image: UIImage(data: observation.image!)!,
                confidence: observation.confidence
            )
            
            uiView.addAnnotation(annotation)
        }
    }
    
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        
        let reuseId = "observation"
        let annotationView = ObservationAnnotationView(annotation: annotation, reuseIdentifier: reuseId)
        annotationView.canShowCallout = true
        
        print("Here")
        
        return annotationView
    }
}

Thank you!

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Answer 1

OOPer OP

Oct ’20

In the mapView method I am not being able to perform that print statement. I can't figure out why.

You are not setting delegate when you instantiate a MKMapView.
The method mapView(_:viewFor:) is a method declared in MKMapViewDelegate, unless setting delegate to MKMapView, it is not called.

You need to define a class which works as a delegate of MKMapView,
move the method mapView(_:viewFor:) into the class,
and set the instance of it when instantiating a MKMapView.

One more thing, you should better use dequeueReusableAnnotationView(withIdentifier:), for performance reason.
To utilize it, your code should be ready for reuse an MKAnnotationView which is instantiated with annotation nil.

Your code would look like this:

Code Block class ObservationAnnotationView: MKAnnotationView {
    //No subclassing needed...
}
struct MyObservationsMap: UIViewRepresentable {
    
    var observationList: [Observation]
    
    static let reuseId = "observation"
    //Define a class which works as a delegate
    class MyMapViewDelegate: NSObject, MKMapViewDelegate {
        func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
            let annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: reuseId, for: annotation) as! ObservationAnnotationView
            if let observationAnnotation = annotation as? ObservationAnnotation {
                
                annotationView.image = observationAnnotation.image
            }
            annotationView.canShowCallout = true
            
            print("Here")
            
            return annotationView
        }
    }
    
    //Instantiate the delegate class
    var mapViewDelegate: MKMapViewDelegate = MyMapViewDelegate()
    func makeUIView(context: Context) -> MKMapView {
        let mapView = MKMapView(frame: .zero)
        mapView.delegate = mapViewDelegate //<- Set delegate
        mapView.register(ObservationAnnotationView.self, forAnnotationViewWithReuseIdentifier: MyObservationsMap.reuseId)
        addAnnotations(to: mapView)
        return mapView
    }
    
    func updateUIView(_ uiView: MKMapView, context: Context) {
        //No need to add annotations here...
    }
        
    func addAnnotations(to mapView: MKMapView) {
        for observation in observationList {
            
            let annotation = ObservationAnnotation(
                coordinate: CLLocationCoordinate2D(latitude: observation.latitude, longitude: observation.longitude),
                species: observation.speciesName!,
                image: UIImage(data: observation.image!)!,
                confidence: observation.confidence
            )
            
            mapView.addAnnotation(annotation)
        }
    }
    //...
}

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