Dynamically style interactive points

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: 37.090240, longitude: -95.712891), zoomLevel: 2, animated: false)
mapView.delegate = self
view.addSubview(mapView)
 
// Add a single tap gesture recognizer. This gesture requires the built-in MGLMapView tap gestures (such as those for zoom and annotation selection) to fail.
let singleTap = UITapGestureRecognizer(target: self, action: #selector(handleMapTap(sender:)))
for recognizer in mapView.gestureRecognizers! where recognizer is UITapGestureRecognizer {
singleTap.require(toFail: recognizer)
}
mapView.addGestureRecognizer(singleTap)
}
 
func mapView(_ mapView: MGLMapView, didFinishLoading style: MGLStyle) {
fetchPoints() { [weak self] (features) in
self?.addItemsToMap(features: features)
}
}
 
func addItemsToMap(features: [MGLPointFeature]) {
// MGLMapView.style is optional, so you must guard against it not being set.
guard let style = mapView.style else { return }
 
// You can add custom UIImages to the map style.
// These can be referenced by an MGLSymbolStyleLayer’s iconImage property.
style.setImage(UIImage(named: "lighthouse")!, forName: "lighthouse")
 
// Add the features to the map as a shape source.
let source = MGLShapeSource(identifier: "us-lighthouses", features: features, options: nil)
style.addSource(source)
 
let lighthouseColor = UIColor(red: 0.08, green: 0.44, blue: 0.96, alpha: 1.0)
 
// Use MGLCircleStyleLayer to represent the points with simple circles.
// In this case, we can use style functions to gradually change properties between zoom level 2 and 7: the circle opacity from 50% to 100% and the circle radius from 2pt to 3pt.
 
let circles = MGLCircleStyleLayer(identifier: "lighthouse-circles", source: source)
circles.circleColor = NSExpression(forConstantValue: lighthouseColor)
 
// The circles should increase in opacity from 0.5 to 1 based on zoom level.
circles.circleOpacity = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)", [2: 0.5, 7: 1])
circles.circleRadius = NSExpression(format: "mgl_step:from:stops:($zoomLevel, 1, %@)", [2: 2, 7: 3])
 
// Use MGLSymbolStyleLayer for more complex styling of points including custom icons and text rendering.
let symbols = MGLSymbolStyleLayer(identifier: "lighthouse-symbols", source: source)
symbols.iconImageName = NSExpression(forConstantValue: "lighthouse")
symbols.iconColor = NSExpression(forConstantValue: lighthouseColor)
symbols.iconScale = NSExpression(forConstantValue: 0.5)
symbols.iconHaloColor = NSExpression(forConstantValue: UIColor.white.withAlphaComponent(0.5))
symbols.iconHaloWidth = NSExpression(forConstantValue: 1)
symbols.iconOpacity = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",
[5.9: 0, 6: 1])
 
// "name" references the "name" key in an MGLPointFeature’s attributes dictionary.
symbols.text = NSExpression(forKeyPath: "name")
symbols.textColor = symbols.iconColor
symbols.textFontSize = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",
[10: 10, 16: 16])
symbols.textTranslation = NSExpression(forConstantValue: NSValue(cgVector: CGVector(dx: 10, dy: 0)))
symbols.textOpacity = symbols.iconOpacity
symbols.textHaloColor = symbols.iconHaloColor
symbols.textHaloWidth = symbols.iconHaloWidth
symbols.textJustification = NSExpression(forConstantValue: NSValue(mglTextJustification: .left))
symbols.textAnchor = NSExpression(forConstantValue: NSValue(mglTextAnchor: .left))
 
style.addLayer(circles)
style.addLayer(symbols)
}
 
// MARK: - Feature interaction
@objc @IBAction func handleMapTap(sender: UITapGestureRecognizer) {
if sender.state == .ended {
// Limit feature selection to just the following layer identifiers.
let layerIdentifiers: Set = ["lighthouse-symbols", "lighthouse-circles"]
 
// Try matching the exact point first.
let point = sender.location(in: sender.view!)
for feature in mapView.visibleFeatures(at: point, styleLayerIdentifiers: layerIdentifiers)
where feature is MGLPointFeature {
guard let selectedFeature = feature as? MGLPointFeature else {
fatalError("Failed to cast selected feature as MGLPointFeature")
}
showCallout(feature: selectedFeature)
return
}
 
let touchCoordinate = mapView.convert(point, toCoordinateFrom: sender.view!)
let touchLocation = CLLocation(latitude: touchCoordinate.latitude, longitude: touchCoordinate.longitude)
 
// Otherwise, get all features within a rect the size of a touch (44x44).
let touchRect = CGRect(origin: point, size: .zero).insetBy(dx: -22.0, dy: -22.0)
let possibleFeatures = mapView.visibleFeatures(in: touchRect, styleLayerIdentifiers: Set(layerIdentifiers)).filter { $0 is MGLPointFeature }
 
// Select the closest feature to the touch center.
let closestFeatures = possibleFeatures.sorted(by: {
return CLLocation(latitude: $0.coordinate.latitude, longitude: $0.coordinate.longitude).distance(from: touchLocation) < CLLocation(latitude: $1.coordinate.latitude, longitude: $1.coordinate.longitude).distance(from: touchLocation)
})
if let feature = closestFeatures.first {
guard let closestFeature = feature as? MGLPointFeature else {
fatalError("Failed to cast selected feature as MGLPointFeature")
}
showCallout(feature: closestFeature)
return
}
 
// If no features were found, deselect the selected annotation, if any.
mapView.deselectAnnotation(mapView.selectedAnnotations.first, animated: true)
}
}
 
func showCallout(feature: MGLPointFeature) {
let point = MGLPointFeature()
point.title = feature.attributes["name"] as? String
point.coordinate = feature.coordinate
 
// Selecting an feature that doesn’t already exist on the map will add a new annotation view.
// We’ll need to use the map’s delegate methods to add an empty annotation view and remove it when we’re done selecting it.
mapView.selectAnnotation(point, animated: true, completionHandler: nil)
}
 
// MARK: - MGLMapViewDelegate
 
func mapView(_ mapView: MGLMapView, annotationCanShowCallout annotation: MGLAnnotation) -> Bool {
return true
}
 
func mapView(_ mapView: MGLMapView, didDeselect annotation: MGLAnnotation) {
mapView.removeAnnotations([annotation])
}
 
func mapView(_ mapView: MGLMapView, viewFor annotation: MGLAnnotation) -> MGLAnnotationView? {
// Create an empty view annotation. Set a frame to offset the callout.
return MGLAnnotationView(frame: CGRect(x: 0, y: 0, width: 20, height: 20))
}
 
// MARK: - Data fetching and parsing
 
func fetchPoints(withCompletion completion: @escaping (([MGLPointFeature]) -> Void)) {
// Wikidata query for all lighthouses in the United States: http://tinyurl.com/zrl2jc4
let query = "SELECT DISTINCT ?item " +
"?itemLabel ?coor ?image " +
"WHERE " +
"{ " +
"?item wdt:P31 wd:Q39715 . " +
"?item wdt:P17 wd:Q30 . " +
"?item wdt:P625 ?coor . " +
"OPTIONAL { ?item wdt:P18 ?image } . " +
"SERVICE wikibase:label { bd:serviceParam wikibase:language \"en\" } " +
"} " +
"ORDER BY ?itemLabel"
 
let characterSet = NSMutableCharacterSet()
characterSet.formUnion(with: CharacterSet.urlQueryAllowed)
characterSet.removeCharacters(in: "?")
characterSet.removeCharacters(in: "&")
characterSet.removeCharacters(in: ":")
 
let encodedQuery = query.addingPercentEncoding(withAllowedCharacters: characterSet as CharacterSet)!
 
let request = URLRequest(url: URL(string: "https://query.wikidata.org/sparql?query=\(encodedQuery)&format=json")!)
 
URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
guard error == nil else {
preconditionFailure("Failed to load GeoJSON data: \(error!)")
}
 
guard
let data = data,
let json = try? JSONSerialization.jsonObject(with: data, options: []) as? [String: AnyObject],
let results = json["results"] as? [String: AnyObject],
let items = results["bindings"] as? [[String: AnyObject]]
else {
preconditionFailure("Failed to parse GeoJSON data")
}
 
DispatchQueue.main.async {
completion(self.parseJSONItems(items: items))
}
}).resume()
}
 
func parseJSONItems(items: [[String: AnyObject]]) -> [MGLPointFeature] {
var features = [MGLPointFeature]()
for item in items {
guard let label = item["itemLabel"] as? [String: AnyObject],
let title = label["value"] as? String else { continue }
guard let coor = item["coor"] as? [String: AnyObject],
let point = coor["value"] as? String else { continue }
 
let parsedPoint = point.replacingOccurrences(of: "Point(", with: "").replacingOccurrences(of: ")", with: "")
let pointComponents = parsedPoint.components(separatedBy: " ")
let coordinate = CLLocationCoordinate2D(latitude: Double(pointComponents[1])!, longitude: Double(pointComponents[0])!)
let feature = MGLPointFeature()
feature.coordinate = coordinate
feature.title = title
// A feature’s attributes can used by runtime styling for things like text labels.
feature.attributes = [
"name": title
]
features.append(feature)
}
return features
}
}