function returns after changing Firebase observer SWIFT 4

Question

I'm rewriting my firebase functions to put in it's own function the realtime part of getting data fro database, so I changed from .observe(.childAdded, with: {(snapshot) in to .observeSingleEvent(of: .value, with: { (snapshot) in in referencing to database. The function now is returning on guard let data = snapshot.value as? [String :String] else { return }when it wasn't before.. What has changed when snapshot is the same? Any explanation of it wold be great as I don't see it myself. Many thanks as always.

Here are the two versions of the function:

Old observer:

func displayAlerts(setCompletion: @escaping (Bool) -> ()) {
        self.mapView.removeAnnotations(mapView.annotations)
        MapArray.alertNotificationCoordinatesArray.removeAll()
        self.userAlertNotificationArray.removeAll()
        print("                     MapArray.alertNotificationCoordinatesArray before snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
        print("                     self.userAlertNotificationArray before snapshot is: \(self.userAlertNotificationArray)")

        ref = Database.database().reference()

        databaseHandle = ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observe(.childAdded, with: { (snapshot) in


            //            self.mapView.removeAnnotations(self.mapView.annotations) //
            print("         snapshot is: \(snapshot)")
            guard let data = snapshot.value as? [String:String] else { return }
            guard let firebaseKey = snapshot.key as? String else { return }
            //                let date = data!["Date"]
            //                let time = data!["Time"]
            let dataLatitude = data["Latitude"]!
            let dataLongitude = data["Longitude"]!

            let type = data["Description"]!
            let id = Int(data["Id"]!)
            let doubledLatitude = Double(dataLatitude)
            let doubledLongitude = Double(dataLongitude)
            let recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude!, longitude: doubledLongitude!)

            print("Firebase alerts posts retrieved")

            let userAlertAnnotation = UserAlert(type: type, coordinate: recombinedCoordinate, firebaseKey: firebaseKey, title: type,id: id!)

            self.userAlertNotificationArray.append(userAlertAnnotation)  // array of notifications coming from Firebase
            //            print("userAlertNotificationArray after retrieving from Firebase is : \(self.userAlertNotificationArray)")

            MapArray.alertNotificationCoordinatesArray.append(recombinedCoordinate) // array for checkig alerts on route


            print("                 MapArray.alertNotificationCoordinatesArray after snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
            print("                     self.userAlertNotificationArray after snapshot is: \(self.userAlertNotificationArray)")
            setCompletion(true)
            self.mapView.addAnnotations(self.userAlertNotificationArray)
        })

    }

New observer:

func displayAlerts(setCompletion: @escaping (Bool) -> ()) {
    print("                     MapArray.alertNotificationCoordinatesArray before newer displayAlert snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
    print("                     self.userAlertNotificationArray before displayAlert snapshot is: \(self.userAlertNotificationArray)")

    if self.userAlertNotificationArray.count == 0 {
       ref = Database.database().reference()

        ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observeSingleEvent(of: .value, with: { (snapshot) in


            //            self.mapView.removeAnnotations(self.mapView.annotations) //
            print("         snapshot is: \(snapshot)")
            guard let data = snapshot.value as? [String :Any] else { return }
            guard let firebaseKey = snapshot.key as? String else { return }
            //                let date = data!["Date"]
            //                let time = data!["Time"]
            let dataLatitude = data["Latitude"] as! Double
            let dataLongitude = data["Longitude"] as! Double

            let type = data["Description"] as! String
            let id = Int(data["Id"] as! String)
            let doubledLatitude = Double(dataLatitude)
            let doubledLongitude = Double(dataLongitude)
            let recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude, longitude: doubledLongitude)

                        print("Firebase alerts posts retrieved")

            let userAlertAnnotation = UserAlert(type: type, coordinate: recombinedCoordinate, firebaseKey: firebaseKey, title: type,id: id!)

            self.userAlertNotificationArray.append(userAlertAnnotation)  // array of notifications coming from Firebase

            MapArray.alertNotificationCoordinatesArray.append(recombinedCoordinate) // array for checkig alerts on route


            print("                 MapArray.alertNotificationCoordinatesArray after newer displayAlert snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
            print("                     self.userAlertNotificationArray after newer displayAlert snapshot is: \(self.userAlertNotificationArray)")
            self.mapView.addAnnotations(self.userAlertNotificationArray)
            setCompletion(true)

        })
    }
}

EDIT:

here are the prints from snapshots so to see results of the two versions:

observeSingleEvent snapshot:

snapshot is: Snap (Alert Notifications) {
    "-LZtTuFSKMhhXFwyT-7K" =     {
        Description = "Ciclabile chiusa";
        Id = 0;
        Latitude = "44.50139187990401";
        Longitude = "11.33592981426992";
    };
    "-LZtUV8MOxVrvPnEfi4g" =     {
        Description = "Lavori in corso";
        Id = 1;
        Latitude = "44.5013918797401";
        Longitude = "11.335929814371545";
    };
    "-LZtV7sJJrOQjAimszTm" =     {
        Description = "Pericoli sulla ciclabile";
        Id = 2;
        Latitude = "44.50139187974223";
        Longitude = "11.335929814367324";
    };
}

and the childAdded snapshots:

snapshot is: Snap (-LZtTuFSKMhhXFwyT-7K) {
    Description = "Ciclabile chiusa";
    Id = 0;
    Latitude = "44.50139187990401";
    Longitude = "11.33592981426992";
}

snapshot is: Snap (-LZtUV8MOxVrvPnEfi4g) {
    Description = "Lavori in corso";
    Id = 1;
    Latitude = "44.5013918797401";
    Longitude = "11.335929814371545";
}

snapshot is: Snap (-LZtV7sJJrOQjAimszTm) {
    Description = "Pericoli sulla ciclabile";
    Id = 2;
    Latitude = "44.50139187974223";
    Longitude = "11.335929814367324";
}

Answer 1

Change

guard let data = snapshot.value as? [String :String] else { return }

to

guard let data = snapshot.value as? [String :[String:String]] else { return } 
data.values.forEach {  
    print($0["Latitude"]) 
    print($0["Longitude"])  
}