Add a line annotation from GeoJSON

import Mapbox
 
class ViewController: UIViewController, MGLMapViewDelegate {
var mapView: MGLMapView!
 
override func viewDidLoad() {
super.viewDidLoad()
 
mapView = MGLMapView(frame: view.bounds)
mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
 
mapView.setCenter(CLLocationCoordinate2D(latitude: 45.5076, longitude: -122.6736),
zoomLevel: 11, animated: false)
view.addSubview(self.mapView)
 
mapView.delegate = self
 
drawPolyline()
}
 
func drawPolyline() {
// Parsing GeoJSON can be CPU intensive, do it on a background thread
 
DispatchQueue.global(qos: .background).async(execute: {
// Get the path for example.geojson in the app's bundle
let jsonPath = Bundle.main.path(forResource: "example", ofType: "geojson")
let url = URL(fileURLWithPath: jsonPath!)
 
do {
// Convert the file contents to a shape collection feature object
let data = try Data(contentsOf: url)
 
guard let shapeCollectionFeature = try MGLShape(data: data, encoding: String.Encoding.utf8.rawValue) as? MGLShapeCollectionFeature else {
fatalError("Could not cast to specified MGLShapeCollectionFeature")
}
 
if let polyline = shapeCollectionFeature.shapes.first as? MGLPolylineFeature {
// Optionally set the title of the polyline, which can be used for:
//  - Callout view
//  - Object identification
polyline.title = polyline.attributes["name"] as? String
 
// Add the annotation on the main thread
DispatchQueue.main.async(execute: {
// Unowned reference to self to prevent retain cycle
[unowned self] in
self.mapView.addAnnotation(polyline)
})
}
} catch {
print("GeoJSON parsing failed")
}
 
})
 
}
 
func mapView(_ mapView: MGLMapView, alphaForShapeAnnotation annotation: MGLShape) -> CGFloat {
// Set the alpha for all shape annotations to 1 (full opacity)
return 1
}
 
func mapView(_ mapView: MGLMapView, lineWidthForPolylineAnnotation annotation: MGLPolyline) -> CGFloat {
// Set the line width for polyline annotations
return 2.0
}
 
func mapView(_ mapView: MGLMapView, strokeColorForShapeAnnotation annotation: MGLShape) -> UIColor {
// Give our polyline a unique color by checking for its `title` property
if (annotation.title == "Crema to Council Crest" && annotation is MGLPolyline) {
// Mapbox cyan
return UIColor(red: 59/255, green: 178/255, blue: 208/255, alpha: 1)
} else {
return .red
}
}
}