Type '()' cannot conform to 'MapAnnotationProtocol' - swiftui

Question

I wrote a demo program to display pins on a map in SwiftUI following this and this tutorial and it worked no problem. Then when I applied this same technique to my app, I get an error that the type cannot conform to 'MapAnnotationProtocol'.
Here's my code:
import SwiftUI
import MapKit
struct MapLocationView: View {
#ObservedObject var manager = LocationManager()
#FetchRequest(sortDescriptors: [])
private var meals: FetchedResults<Meal>
var body: some View {
Map(coordinateRegion: $manager.region, annotationItems: meals) { meal in // error is on Map
if (meal.latitude != 0 && meal.longitude != 0) {
let coordinate = CLLocationCoordinate2D(latitude: meal.latitude, longitude: meal.longitude)
MapPin(coordinate: coordinate)
}
}
}
}
The LocationManager code is the same, unaltered code from the tutorial and from the demo I wrote. I don't understand why it works in the demo and doesn't work in my app.
I've tried wrapping the code in a Group {} but that didn't fix it. I've read other articles with similar error messages but none of those solutions seemed to apply in this case.
I'm pretty new to Swift and SwiftUI so it makes no sense to me that it should work in the demo but not in my app. I hope I've provided enough information for the problem to make sense.

Answer 1

A couple of things come to mind while looking at your code:
Does Meal conform to Identifiable?
Your closure should always return some sort of map annotation.
Your MapPin(.. ) should work, but it looks like you'll need to filter your array of Meal structs before that closure is called.
The following is untested code, but might help anyway.
extension Meal: Identifiable {
var id: ObjectIdentifier {
return ObjectIdentifier(self)
}
}
extension Meal {
var isValid: Bool {
return latitude != 0 && longitude != 0
}
var coordinate: CLLocationCoordinate2D {
return CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
}
var body: some View {
Map(coordinateRegion:
$manager.region,
annotationItems: meals.filter { $0.isValid ) { meal in
MapPin(coordinate: meal.coordinate)
}
}