fetching locations points and title and showing on mapkit view

Question

I add places using a longtapgesture recognizer and while it shows on my map, it dissapears when i leave the view and then comeback.

so I'm adding the locations using firebase fetching the location and I want it to show on my mapview. I'm getting the values on snapshot.value and i'm trying to showcase on my mapview, please help me. this is the last step that I can't seem to figure out.

 func fetchlocations() {
    let ref = Database.database().reference()
    ref.child("Map").observe(.value) { (snapshot) in
        print(snapshot.value)

        let activity = (snapshot.value as AnyObject!)!["activity"] as? String?
        let lat = (snapshot.value as AnyObject!)!["lat"] as? String?
        let long = (snapshot.value as AnyObject!)!["long"] as? String?

        let annotation = MKPointAnnotation()
        annotation.coordinate = CLLocationCoordinate2D(latitude: (Double(lat!))!, longitude: (Double(long!))!)
        annotation.title = activity
        self.mapView?.addAnnotation(annotation)
    }
}