Swift Properties

Question

So, while learning swift, I've run into an issue with adding values to an array property. When I try to print the first value of the array after adding a value to it, I receive an index out of bounds error. How do I add a value to an array property that is accessible to the entire class?

class HomeViewController: UIViewController {

    var geofences = [Geofence]()

    override func viewDidLoad() {
        super.viewDidLoad()
        getFences()
        print(self.geofences[0])
    }

    func getFences() {
        var query = PFQuery(className:"Geofence")
        query.whereKey("username", equalTo: "Peter")
        query.findObjectsInBackgroundWithBlock {
            (fences: [PFObject]?, error: NSError?) -> Void in
            if error == nil && fences != nil {
                if let fences = fences {
                    for (index, element) in fences.enumerate() {
                        var unique_id = element.objectId
                        var fence_radius = element["radius"] as! Int
                        var fence_name = element["name"] as! String
                        var lat = element["centerPoint"].latitude
                        var lon = element["centerPoint"].longitude
                        var center = CLLocationCoordinate2D(latitude: lat, longitude: lon)
                        var new_fence: Geofence? = Geofence(uniqueID: unique_id!, radius: fence_radius, centerPoint: center, name: fence_name)
                        self.geofences.append(new_fence!)
                    }
                }
            } else {
                print(error)
            }
        }
    }

EDIT: It seems I oversimplified the issue. Here is the code that's getting the index out of bounds error. When I retrieve the geofence from Parse, the geofences array is populated, but once it exits the getFences method, the array is emptied.

Answer 1

It's likely that your print call is being run before getFences() has had time to populate the array. You can check this with another print call outside of query.findObjectsInBackgroundWithBlock