Swift Using NotificationCenter to Pass Data Between View Controllers - swift

Question

I am trying to pass the data of user-input coordinates from one VC to another using Notifications. When I run the code, it does not add an annotation onto the MapView, so I have a hunch I may have not set up the notification to send with the inputted coordinates properly, but I am not sure where I have went wrong.
Class file that takes the input of coordinates:
import UIKit
import CoreLocation
var locations: [Dictionary<String, Any>] = [] // here I initialize my empty array of locations
class OtherVC: UIViewController {
#IBOutlet weak var latitudeField: UITextField!
#IBOutlet weak var longitudeField: UITextField!
#IBOutlet weak var titleTextField: UITextField!
var coordinates = [CLLocationCoordinate2D]()
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func addToMap(_ sender: Any) {
let lat = latitudeField.text!
let long = longitudeField.text!
let title = titleTextField.text!
var location: [String: Any] = ["title": title, "latitude": lat, "longitude": long]
locations.append(location)
NotificationCenter.default.post(name: NSNotification.Name("MapViewController.coordinate.updated"), object: locations, userInfo: nil)
}
}
Class file that receives notification and places annotation:
import UIKit
import MapKit
class MapViewController: UIViewController, MKMapViewDelegate {
#IBOutlet weak var mapView: MKMapView!
override func viewDidLoad() {
super.viewDidLoad()
mapView.delegate = self
}
func add(notification: NSNotification) {
let dict = notification.object as! NSDictionary
// takes the coordinates from the notification and converts such that the map can interpret them
let momentaryLat = (dict["latitude"] as! NSString).doubleValue
let momentaryLong = (dict["longitude"] as! NSString).doubleValue
let annotation = MKPointAnnotation()
annotation.title = dict["title"] as? String
annotation.coordinate = CLLocationCoordinate2D(latitude: momentaryLat as CLLocationDegrees, longitude: momentaryLong as CLLocationDegrees)
mapView.addAnnotation(annotation)
self.mapView.centerCoordinate = annotation.coordinate
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
let identifier = "pinAnnotation"
var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier) as? MKPinAnnotationView
if annotationView == nil {
annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
annotationView?.canShowCallout = true
}
annotationView?.annotation = annotation
return annotationView
}
}

Answer 1

It's the same as the Objective-C API, but uses Swift's syntax.
NSNotificationCenter.defaultCenter().addObserver(
self,
selector: #selector(batteryLevelChanged),
name: UIDeviceBatteryLevelDidChangeNotification,
object: nil)
Or in Swift 3:
NotificationCenter.default.addObserver(
self,
selector: #selector(self.batteryLevelChanged),
name: .UIDeviceBatteryLevelDidChange,
object: nil)
If your observer does not inherit from an Objective-C object, you must prefix your method with #objc in order to use it as a selector.
#objc func batteryLevelChanged(notification: NSNotification){
//do stuff
}

Answer 2

Register obeserver to receive notification in your MapViewController
override func viewDidLoad() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.add(_:)), name: NSNotification.Name("MapViewController.coordinate.updated"), object: nil)
}
Also you can send data using userInfo property of NSNotification or send using custom object.
func add(_ notification: NSNotification) {
...
}
see pass data using nsnotificationcenter