Custom google maps style takes a second to load - ios

Question

I'm implementing a custom style for my google maps view for a bus transit app I'm developing in XCode 9 w/ Swift 4. Whenever I load a map view, it always takes a little less than a second to load the custom style and I'm not sure what's causing this to happen.
Here's the effect I'm describing:
As you can see, the tan background is the default style for google's mapview, and it's visible for only a small period of time.
Here's my code that implements the map view:
class StopPredictionVC: UIViewController {
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
setUpMapView()
}
private func setUpMapView() {
let stopLatitude = Double(stop!.lat)
let stopLongitude = Double(stop!.lon)
let camera = GMSCameraPosition.camera(withLatitude: stopLatitude!, longitude: stopLongitude!, zoom: 16.4)
let frame = CGRect(x: 0, y: 0, width: self.view.bounds.width, height: self.view.bounds.height)
mapView = GMSMapView.map(withFrame: frame, camera: camera)
let nightModeEnabled = APIWrapper.sharedInstance.settings.nightMode!
if nightModeEnabled {
mapView.mapStyle(withFilename: "nightStyle", andType: "json")
} else {
mapView.mapStyle(withFilename: "mapStyle", andType: "json")
}
let marker = GMSMarker()
marker.icon = #imageLiteral(resourceName: "marker")
marker.appearAnimation = .pop
marker.position = CLLocationCoordinate2D(latitude: stopLatitude!, longitude: stopLongitude!)
marker.title = "Bus Stop Name"
marker.snippet = "Example description"
marker.map = mapView
buildRoute(routePath: routeConfig!.path)
view.addSubview(mapView)
}
}
extension GMSMapView {
func mapStyle(withFilename name: String, andType type: String) {
do {
if let styleURL = Bundle.main.url(forResource: name, withExtension: type) {
self.mapStyle = try GMSMapStyle(contentsOfFileURL: styleURL)
} else {
NSLog("Unable to find style.json")
}
} catch {
NSLog("One or more of the map styles failed to load. \(error)")
}
}
}
buildRoute(routePath:) is a function that builds the blue colored path on the road if anyone was wondering.
Obviously this isn't a huge bug, but it's quite frustrating to see every time I load a map view. Anyone see anything in my code that could be causing this?

Answer 1

You call it inside viewWillAppear it has 2 problems , first it's called after viewDidLoad (has some delay) , second it may be called every time the VC is shown such as returning from a push / dismiss Modal
so call setUpMapView inside viewDidLoad
note this buildRoute(routePath: routeConfig!.path) should be in a background queue if it calls any web service or do any long job inside mainQueue
BTW i may also try to load
GMSMapStyle(contentsOfFileURL: styleURL)
in background thread and after load set in mainQueue and that only if using GMSMapStyle is allowed inside a back thread