Inherit MGLPolygon in Mapbox iOS SDK 3.3.1 - ios

Question

I'm trying to define a class Building which inherits MGLPolygon.
MGLPolygon is defined as:
public class MGLPolygon : MGLMultiPoint, MGLOverlay {
public var interiorPolygons: [MGLPolygon]? { get }
public convenience init(coordinates coords: UnsafeMutablePointer<CLLocationCoordinate2D>, count: UInt)
public convenience init(coordinates coords: UnsafeMutablePointer<CLLocationCoordinate2D>, count: UInt, interiorPolygons: [MGLPolygon]?)
}
MGLPolygon's designated initializer is hidden in the swift version of SDK. The following would fail:
class Building: MGLPolygon {
let name: String
init(name: String, coordinates: [CLLocationCoordinate2D]){
self.name = name
super.init(coordinates: &coordinates, count: UInt(coordinates.count))
// Must call a designated initializer of the superclass 'MGLPolygon'
}
}
I checked the original SDK code in Objective-C:
#implementation MGLPolygon
#dynamic overlayBounds;
+ (instancetype)polygonWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count {
return [self polygonWithCoordinates:coords count:count interiorPolygons:nil];
}
+ (instancetype)polygonWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count interiorPolygons:(NSArray<MGLPolygon *> *)interiorPolygons {
return [[self alloc] initWithCoordinates:coords count:count interiorPolygons:interiorPolygons];
}
- (instancetype)initWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count interiorPolygons:(NSArray<MGLPolygon *> *)interiorPolygons {
if (self = [super initWithCoordinates:coords count:count]) {
if (interiorPolygons.count) {
_interiorPolygons = interiorPolygons;
}
}
return self;
}
- (mbgl::LinearRing<double>)ring {
NSUInteger count = self.pointCount;
CLLocationCoordinate2D *coordinates = self.coordinates;
mbgl::LinearRing<double> result;
result.reserve(self.pointCount);
for (NSUInteger i = 0; i < count; i++) {
result.push_back(mbgl::Point<double>(coordinates[i].longitude, coordinates[i].latitude));
}
return result;
}
- (mbgl::Annotation)annotationObjectWithDelegate:(id <MGLMultiPointDelegate>)delegate {
mbgl::Polygon<double> geometry;
geometry.push_back(self.ring);
for (MGLPolygon *polygon in self.interiorPolygons) {
geometry.push_back(polygon.ring);
}
mbgl::FillAnnotation annotation { geometry };
annotation.opacity = [delegate alphaForShapeAnnotation:self];
annotation.outlineColor = [delegate strokeColorForShapeAnnotation:self];
annotation.color = [delegate fillColorForPolygonAnnotation:self];
return annotation;
}
#end
However, unfortunately I'm not good with Objective-C and I don't understand the code.
What am I asking?
What is the designated initializer of MGLPolygon in Swift? What does it take as parameters?
Extra question
Why is the designated initializer hidden?

Answer 1

I think you will need to create a class method in your subclass (e.g. +buildingWithCoordinates:count:) which calls super's implementation in order to handle this.

Answer 2

My solution according to #incanus's advice:
class Building: MGLPolygon {
var name: String?
afterInit(name: String){
self.name = name
}
}
func initBuilding(name: String, coordinates: [CLLocationCoordinate2D]) -> Building {
let building = Building(coordinates: &coordinates, count: UInt(coordinates.count))
building.afterInit(name)
return building
}
It's not elegant but it works.