Add a pattern to a polygon

import Mapbox
 
class ViewController: UIViewController, MGLMapViewDelegate {
 
override func viewDidLoad() {
super.viewDidLoad()
 
// Set the map’s size, style, center coordinate, zoom level, and tint color.
let mapView = MGLMapView(frame: view.bounds)
mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
mapView.styleURL = MGLStyle.darkStyleURL(withVersion: 9)
mapView.setCenter(CLLocationCoordinate2D(latitude: 38.849534447, longitude: -77.039222717), zoomLevel: 8.5, animated: false)
mapView.tintColor = .lightGray
 
view.addSubview(mapView)
 
mapView.delegate = self
}
 
func mapView(_ mapView: MGLMapView, didFinishLoading style: MGLStyle) {
 
// Set the UIImage to be used for the fill pattern.
let fillPatternImage = UIImage(named: "stripe-pattern")!
 
// Add the fill pattern image to used by the style layer.
style.setImage(fillPatternImage, forName: "stripe-pattern")
 
// "mapbox://examples.0cd7imtl" is a map ID referencing a tileset containing vector data.
// For more information, see mapbox.com/help/define-map-id/
let source = MGLVectorTileSource(identifier: "drone-restrictions", configurationURL: URL(string: "mapbox://examples.0cd7imtl")!)
style.addSource(source)
 
// Create a style layer using the vector source.
let layer = MGLFillStyleLayer(identifier: "drone-restrictions-style", source: source)
 
// Set the source's identifier using the source name retrieved from its
// TileJSON metadata: mapbox.com/api-documentation/maps/#retrieve-tilejson-metadata
// You can also retrieve the source layer identifier in the Mapbox Studio layers list,
// if your source data was added using the Mapbox Studio style editor.
layer.sourceLayerIdentifier = "drone-restrictions-3f6lsg"
 
// Set the fill pattern and opacity for the style layer. The NSExpression
// object is a generic container for a style attribute value. In this case,
// it is a reference to the fillPatternImage.
layer.fillPattern = NSExpression(forConstantValue: "stripe-pattern")
layer.fillOpacity = NSExpression(forConstantValue: 0.5)
 
// Insert the pattern style layer below the layer contining city labels. If the
// layer is not found, the style layer will be added above all other layers within the
// Mapbox Dark style. NOTE: The "place-city-sm" layer is specific to the Mapbox Dark style.
// Refer to the layers list in Mapbox Studio to confirm which layers are available for
// use when working with a custom style.
if let cityLabels = style.layer(withIdentifier: "place-city-sm") {
style.insertLayer(layer, below: cityLabels)
} else {
style.addLayer(layer)
}
}
}