Pfthb

I'm trying to set up a class that inherits from MKPolygon as below, but the compiler rejects my call to super.init() with the following error message:

Must call a designated initializer of the superclass 'MKPolygon'

What is the designated initializer for MKPolygon?

Following the advice of this answer and this one, I've scoured the class documentation. There are four initializers available but all of them are declared as Convenience Initializers.

• init(points: UnsafePointer, count: Int)
  


• init(points: UnsafePointer, count: Int, interiorPolygons: [MKPolygon]?)
  


• init(coordinates: UnsafePointer, count: Int)
  


• init(coordinates: UnsafePointer, count: Int, interiorPolygons: [MKPolygon]?)
  

I'm fairly new to Swift so I'm sure there's something simple I'm missing.

My subclass implementation is below, in case that helps.

import MapKit
import UIKit

class AudioGuideRegionAnnotation: MKPolygon 

 // MARK: - Properties
 let color: UIColor
 let image: UIImage?

 // MARK: - Initializers
 init(region: AudioGuideRegion) 
 var locations = region.locations
 super.init(coordinates: &locations, count: locations.count) // <-- rejected with "Must call a designated initializer of the superclass 'MKPolygon'"
 self.title = region.title
 self.subtitle = "(Int(round(Double(region.duration / 60)))) minutes"
 self.color = .black
 self.image = region.images.first?.image
 super.init()
 

Following Matt's helpful comment above, it turns out the answer is that MKPolygon and several other classes do not have accessible designated initializers.

In such a case subclassing is not possible, and the only course of action appears to be to extend the class you intended to subclass.

This answer, linked to by Matt is supremely helpful as further reading.