Why is my MKCoordinateRegion nil? - ios

Question

So I've got the following function to set my map region for my app:
func mapRegion() -> MKCoordinateRegion {
databaseHandle = databaseRef.child("RunList").child(runName).observe(.value, with: { (snapshot) in
let runData = snapshot.value as? [String: AnyObject]
self.minLat = runData?["startLat"] as? Double
self.minLng = runData?["startLong"] as? Double
self.maxLat = runData?["endLat"] as? Double
self.maxLng = runData?["endLong"] as? Double
print("testing")
print(self.minLat!)
print(self.maxLng!)
self.coordinate = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: (self.minLat! + self.maxLat!)/2,
longitude: (self.minLng! + self.maxLng!)/2),
span: MKCoordinateSpan(latitudeDelta: (self.maxLat! - self.minLat!)*1.1,
longitudeDelta: (self.maxLng! - self.minLng!)*1.1))
})
return coordinate
}
I have initialised the following variables at the top of my class:
var minLat: Double!
var minLng: Double!
var maxLat: Double!
var maxLng: Double!
var coordinate: MKCoordinateRegion!
And am trying to set the map region as follows:
override func viewDidLoad() {
super.viewDidLoad()
configureView()
mapView.region = mapRegion()
}
The error I am getting is in the lines where I am setting my coordinate region under the block of code that contains my databaseHandle in mapRegion(). When the code is running, I get the following error under the line 'return coordinate':
fatal error: unexpectedly found nil while unwrapping an Optional value
To my understanding, this is occurring because 'coordinate' has no values and is an Optional. Why is it that coordinate has no values even though I am setting it up using a global variable? I feel like I am missing something so simple!
Thanks

Answer 1

Your code does not work because observe works asynchronously and it is impossible to return a value from a method containing a asynchronous task.
You need a completion handler
func mapRegion(completion: (MKCoordinateRegion)->()) {
databaseHandle = databaseRef.child("RunList").child(runName).observe(.value, with: { (snapshot) in
let runData = snapshot.value as? [String: AnyObject]
self.minLat = runData?["startLat"] as? Double
self.minLng = runData?["startLong"] as? Double
self.maxLat = runData?["endLat"] as? Double
self.maxLng = runData?["endLong"] as? Double
print("testing")
print(self.minLat!)
print(self.maxLng!)
let region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: (self.minLat! + self.maxLat!)/2,
longitude: (self.minLng! + self.maxLng!)/2),
span: MKCoordinateSpan(latitudeDelta: (self.maxLat! - self.minLat!)*1.1,
longitudeDelta: (self.maxLng! - self.minLng!)*1.1))
completion(region)
})
}
And use it
mapRegion() { region in
mapView.region = region
// do other things with the region
}
Side note:
There are too many question marks in the code. Use optional bindings to unwrap optionals safely.