Retrieving data from Firebase and storing as annotations on a map

问题

I've successfully managed to store data to my Firebase database from a form I created in a view controller but now need to retrieve the data to display as annotations on a map on a second view controller but do not know how I should go about doing this task after searching and finding nothing online.

Here is my working code that saves my data successfully to the Firebase database:

import UIKit
import CoreLocation
import Firebase

class AddSightingViewController: UIViewController {

    @IBOutlet weak var dateLabel: UILabel!
    @IBOutlet weak var timeLabel: UILabel!
    @IBOutlet weak var latitudeLabel: UILabel!
    @IBOutlet weak var longitudeLabel: UILabel!
    @IBOutlet weak var descriptionLabel: UITextView!

    var locManager = CLLocationManager()
    var currentLocation: CLLocation!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Set Date & Time

        let dateFormatter = DateFormatter()
        dateFormatter.dateStyle = .medium

        dateFormatter.setLocalizedDateFormatFromTemplate("EEEE, MMM d, yyyy") // // set template after setting locale

        let dateString = "\(dateFormatter.string(from: Date() as Date))"
        dateLabel.text = String(dateString)

        let timeFormatter = DateFormatter()
        timeFormatter.timeStyle = .medium

        timeFormatter.setLocalizedDateFormatFromTemplate("hhmm")

        let timeString = "\(timeFormatter.string(from: Date() as Date))"

        timeLabel.text = String(timeString)

        // Set Latitude & Longitude

        locManager.requestWhenInUseAuthorization()

        if (CLLocationManager.authorizationStatus() == CLAuthorizationStatus.authorizedWhenInUse ||
            CLLocationManager.authorizationStatus() == CLAuthorizationStatus.authorizedAlways){
            currentLocation = locManager.location
            self.latitudeLabel.text = String("\(currentLocation.coordinate.latitude)")
            self.longitudeLabel.text = String("\(currentLocation.coordinate.longitude)")
        }
    }

    func post() {

        let date = dateLabel.text
        let time = timeLabel.text
        let latitude = latitudeLabel.text
        let longitude = longitudeLabel.text
        let sightingDescription = descriptionLabel.text

        let post: [String : AnyObject] = ["Date" : date as AnyObject,
                                          "Time" : time as AnyObject,
                                          "Latitude" : latitude as AnyObject,
                                          "Longitude" : longitude as AnyObject,
                                          "Description" : sightingDescription as AnyObject]

        var ref: DatabaseReference!
        ref = Database.database().reference()
        ref.child("Sightings").childByAutoId().setValue(post)

    }

    @IBAction func saveButton(_ sender: Any) {

        post()

        // Create the alert controller
        let alertController = UIAlertController(title: "Sighting Logged Successfully", message: "Your logged entry will now show up on the map for others to see. Thank You!", preferredStyle: .alert)

        // Create the actions
        let okAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.default) {
            UIAlertAction in
            NSLog("OK Pressed")

        }

        // Add the actions
        alertController.addAction(okAction)

        // Present the controller
        self.present(alertController, animated: true, completion: nil)

    }

}

回答1:

After working on this I've eventually got it to work by using the following function and calling it in viewDidLoad()

func displayAnnotations() {

        let ref = Database.database().reference()
        ref.child("Sightings").observe(.childAdded, with: { (snapshot) in

            let date = (snapshot.value as AnyObject!)!["Date"] as! String!
            let time = (snapshot.value as AnyObject!)!["Time"] as! String!
            let latitude = (snapshot.value as AnyObject!)!["Latitude"] as! String!
            let longitude = (snapshot.value as AnyObject!)!["Longitude"] as! String!
            let desc = (snapshot.value as AnyObject!)!["Description"] as! String!

            let annotation = MKPointAnnotation()

            annotation.coordinate = CLLocationCoordinate2D(latitude: (Double(latitude!))!, longitude: (Double(longitude!))!)
            annotation.title = date
            annotation.subtitle = time
            self.map.addAnnotation(annotation)

        })}

来源：https://stackoverflow.com/questions/44434480/retrieving-data-from-firebase-and-storing-as-annotations-on-a-map