查找选定的MapKit注释的postID

Question

I'm trying to set the selected MapKit's Annotation ID (mapEventID in my case) on didSelect and to use when Swift is preparing the segue:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
   let postViewVC = segue.destination as! PostView
   postViewVC.eventID = mapEventID
}

mapEventID is initialized in the GeoFire observer:

func retrieveAllEvents () {

    let postDB = Database.database().reference().child("DBName")

    postDB.observe(.childAdded) { (snapshot) in

        let snapshotValue =  snapshot.value as! Dictionary <String,AnyObject>
        let postTitle = snapshotValue ["EventTitle"]!
        let postLocation = snapshotValue ["VisibleLocation"]!
        let eventID = snapshotValue ["EventID"]
        let postTime = snapshotValue ["EventDateTimeStart"]!

        let date = self.convertTimestamp(serverTimestamp: postTime as! Double)
        let mapEventDetails : String  = "\(date) - \(postLocation)"

        self.geoFire.getLocationForKey(locationID! as! String) { (location, error) in
            if (error != nil) {
                print("An error occurred getting the location for eventID:", eventID as Any)

            } else if (location != nil) {

                let postLat = location?.coordinate.latitude
                let postLong = location?.coordinate.longitude
                let coordinate = CLLocationCoordinate2D(latitude: postLat!, longitude: postLong!)
                let annotation = EventAnnotation (coordinate: coordinate, withKey: eventID as! String, title: mapEventDetails, subtitle: mapEventDetails)

                self.mapEventID = annotation.eventKey
                self.eventMap.addAnnotation(annotation)

            } else {
                print("GeoFire does not contain a location for:", eventID as Any)
            }
        }
    }
}

The problem is that it always uses the most recently added post's ID as the mapEventID and not the one the user actually tapped on. This makes sense because when the IDs are retrieved from Firebase through the observer it 'observes' for all the keys and the most recent one becomes the ID.

How do I obtain the specific mapEventID when the user taps on the annotation? At the moment I have:

func mapView(_ mapView: MKMapView, didSelect view: MKAnnotationView) {
    mapEventID = //How do I change the EventID here?
} 

I was hoping I could add the ID to the annotation's Description' property in the Geofire observer but Swift does not provide any syntax for that in:

let annotation = EventAnnotation (coordinate: coordinate, withKey: eventID as! String, title: postTitle, subtitle: eventDetails)

Answer 1

Try the following code:

func mapView(_ mapView: MKMapView, didSelect view: MKAnnotationView) {
    if let annotation = view.annotation as? EventAnnotation {
        mapEventID = annotation.eventKey
    }
}