SwiftUI/ MapKit - Populate a MapAnnotation Struct from MongoDB Realm/ Atlas collection - swiftui

Question

I am new to SwiftUI and Realm (using flexible sync), please excuse if it sounds like an elementary question
I have location data saved in a MongoDB Atlas collection - Centre
class Centre: Object, ObjectKeyIdentifiable {
#Persisted var _id: ObjectId = ObjectId.generate()
#Persisted var centreName = ""
#Persisted var centreDesc = ""
#Persisted var centreLocation: Coordinates?
override static func primaryKey() -> String? {
return "_id"
}
convenience init(centreName: String, centreDesc: String, centreLocation: Coordinates) {
self.init()
self.centreName = centreName
self.centreDesc = centreDesc
self.centreLocation = centreLocation
}
}
and Coordinates are embedded objects where "x" is longitude and "y" is latitude
class Coordinates: EmbeddedObject, ObjectKeyIdentifiable {
#Persisted var x: Double?
#Persisted var y: Double?
}
I have created a Struct to conform to the requirements of MapAnnotation protocol as -
struct CustomAnnots: Identifiable {
let id: UUID
var nameCentreLoc: String
var descCentreLoc: String
let latitude: Double
let longitude: Double
var coordinate: CLLocationCoordinate2D {
CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
}
}
I am trying to populate this struct from the data from Atlas collection
My LocationView - not working
import SwiftUI
import MapKit
import RealmSwift
struct LocationView: View {
#Environment(\.realm) var realm
#ObservedResults(Centre.self) var centres
#ObservedRealmObject var centre: Centre
#State private var nameCentreLoc = ""
#State private var descCentreLoc = ""
#State private var latitude = 0.0
#State private var longitude = 0.0
#State private var annots = []
#State private var region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: 24.681_858, longitude: 81.811_623),
span: MKCoordinateSpan(latitudeDelta: 10, longitudeDelta: 10)
)
var body: some View {
Map(coordinateRegion: $region, annotationItems: annots, annotationContent: { locations in
MapPin(coordinate: locations.coordinate)
})
.onAppear {
setSubscription()
initData()
}
}
private func setSubscription() {
let subscriptions = realm.subscriptions
subscriptions.write {
if let currentSubscription = subscriptions.first(named: "all_centres") {
currentSubscription.update(toType: Centre.self) { centre in
centre.centreName != ""
}
} else {
subscriptions.append(QuerySubscription<Centre>(name: "all_centres") { centre in
centre.centreName != ""
})
}
}
}
private func initData() {
nameCentreLoc = centre.centreName
descCentreLoc = centre.centreDesc
latitude = (centre.centreLocation?.y)!
longitude = (centre.centreLocation?.x)!
let annots = [for centre in centres {
CustomAnnots(id: UUID(), nameCentreLoc: nameCentreLoc, descCentreLoc: descCentreLoc, latitude: latitude, longitude: longitude)
}]
}
}
How do I populate the Struct with data from Centre collection?
Changed to (with no errors in Xcode)-
var body: some View {
let annots = [CustomAnnots(id: UUID(), nameCentreLoc: centre.centreName, descCentreLoc: centre.centreDesc, latitude: (centre.centreLocation?.y)!, longitude: (centre.centreLocation?.x)!)]
Map(coordinateRegion: $region, annotationItems: annots, annotationContent: { locations in
MapPin(coordinate: locations.coordinate)
})
.onAppear {
setSubscription()
}
}
now getting runtime error "Force unwrapping nil value"
with this function I am able to print out the results to console
func getLoc() {
for centre in centres {
var annots = [CustomAnnots.init(id: UUID(), nameCentreLoc: centre.centreName, descCentreLoc: centre.centreDesc, latitude: (centre.centreLocation?.y)!, longitude: (centre.centreLocation?.x)!)]
print(annots)
}
}
I get this printed out -
[ACCv5.CustomAnnots(id: 67E9DADA-0BCC-4D30-8136-8B666881E82D, nameCentreLoc: "HO", descCentreLoc: "Head Office Artemis Cardiac Care Gurgaon", latitude: 28.438694893842058, longitude: 77.10845294294181)]
[ACCv5.CustomAnnots(id: 26DC0C63-5A17-49C7-B4BF-FD3AA1ABF65E, nameCentreLoc: "Panipat", descCentreLoc: "Artemis Heart Centre at Ravindra Hospital", latitude: 29.388306713854682, longitude: 76.95889693063663)]
[ACCv5.CustomAnnots(id: D3A70E58-6B65-4F5D-A398-3394B7FB04DF, nameCentreLoc: "Ranchi", descCentreLoc: "Artemis Heart Centre at Raj Hospital", latitude: 23.35731237118492, longitude: 85.32288933068195)]
But I am unable to display MapAnnotations with this -
#Environment(\.realm) var realm
#ObservedResults(Centre.self) var centres
#State public var annots: [CustomAnnots]
#State private var region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: 24.681_858, longitude: 81.811_623),
span: MKCoordinateSpan(latitudeDelta: 10, longitudeDelta: 10)
)
var body: some View {
ForEach (centres) { centre in
var annots = [CustomAnnots.init(id: UUID(), nameCentreLoc: centre.centreName, descCentreLoc: centre.centreDesc, latitude: (centre.centreLocation?.y)!, longitude: (centre.centreLocation?.x)!)]
}
// Text("\(annots.count)")
Map(coordinateRegion: $region, annotationItems: annots, annotationContent: { locations in
MapMarker(coordinate: locations.coordinate)
})
Final code after Jay's suggestions
class Centre: Object, ObjectKeyIdentifiable {
#Persisted var _id: ObjectId = ObjectId.generate()
#Persisted var centreName = ""
#Persisted var centreDesc = ""
#Persisted var centreLocation: Coordinates?
override static func primaryKey() -> String? {
return "_id"
}
convenience init(centreName: String, centreDesc: String, x: Double, y: Double) {
self.init()
self.centreName = centreName
self.centreDesc = centreDesc
self.centreLocation?.x = x
self.centreLocation?.y = y
}
var coordinate: CLLocationCoordinate2D {
CLLocationCoordinate2D(latitude: (centreLocation?.y)!, longitude: (centreLocation?.x)!)
}
}
Map(coordinateRegion: $region, annotationItems: centres, annotationContent: { centre in
MapMarker(coordinate: centre.coordinate)
})

Answer 1

Simplifying may produce a more streamlined solution.
If the objective is to populate a map from Realm objects, then I think you're on the right track but there are too many moving parts - lets reduce that code. Let me know if I misunderstood the question..
Here's some pseudo code:
Start with the Realm object that contains the data. Note we don't need the primary key because we are using ObjectId's for that. This object has everything needed to track the pin on the map, it can be observed for changes and returns a calculated var containing the MapAnnotation to be used on the map itself, based on the data in the object
class Centre: Object, ObjectKeyIdentifiable {
#Persisted var _id: ObjectId = ObjectId.generate()
#Persisted var centreName = ""
#Persisted var centreDesc = ""
#Persisted var x: Double!
#Persisted var y: Double!
var mapAnno: MapAnnotation {
//build the map annotation from the above properties
return //return the map annotation
}
convenience init(centreName: String, centreDesc: String, x: Double, y: Double) {
self.init()
self.centreName = centreName
self.centreDesc = centreDesc
self.x = x
self.y = y
}
}
Then in the view - load up all of the centers and iterate over them retreiving the MapAnnotation from each
#ObservedResults(Centre.self) var centres //loads all of the centrs
var body: some View {
ForEach (centres) { centre in
let mapAnnotation = centre.mapAnno
//add the annotation to the map
Note this pattern is pretty common as well
Map(coordinateRegion: $region,
showsUserLocation: true,
annotationItems: centres) { center in
MapAnnotation(coordinate: //get coords from centre)