Redesign Init (MKAnnotation) - swift

Question

class Point: NSObject, MKAnnotation {
var id: String?
var title: String?
var coordinate: CLLocationCoordinate2D
var subtitle: String?
init(id: String, dictionary: Dictionary<String, AnyObject>){
self.id = id
if let title = dictionary["title"] as? String {
self.title = title
}
if let subtitle = dictionary["subtitle"] as? String {
self.subtitle = subtitle
}
if let coords = dictionary["coordinates"] as? [String:[String:Double]] {
self.coordinate.latitude = coords.values.first!["latitude"]!
self.coordinate.longitude = coords.values.first!["longitude"]!
}
super.init()
}
/*
init(title: String, subtitle: String, coordinate: CLLocationCoordinate2D){
self.title = title
self.subtitle = subtitle
self.coordinate = coordinate
}*/
}
I implemented initializer for creating Point on Map. I must redesign init because I use Firebase and results from database are in dictionary.
It writes: Property self.coordinate not initialized at implicitly generated super.init call

Answer 1

init(id: String, dictionary: Dictionary<String, AnyObject>){
self.id = id
if let title = dictionary["title"] as? String {
self.title = title
}
if let subtitle = dictionary["subtitle"] as? String {
self.subtitle = subtitle
}
if let coords = dictionary["coordinates"] as? [String:[String:Double]] {
self.coordinate.latitude = coords.values.first!["latitude"]!
self.coordinate.longitude = coords.values.first!["longitude"]!
}
super.init()
}
So, the problem here mostly lies in the fact that you only ever initialize your coordinate property within an if. Because coordinate is not marked as an optional, it much be given a value before you call super.init(), as per the rules of Swift initializers.
And because you initialize it within an if only, there's a chance that the if fails and you never initialize it at all. This would leave the instance in a completely invalid state, which is not allowed per the rules of Swift initializers and fails the first safety check.
Safety check 1
A designated initializer must ensure that all of the properties
introduced by its class are initialized before it delegates up to a
superclass initializer.
You could make coordinate an optional instance variable, must like your other instance variables. However, I'd argue that probably makes most sense is that id & title are probably also non-optional, and all of these properties probably should be let constants.
As such, I'd rewrite your class and that initializer as such:
class Point: NSObject, MKAnnotation {
let id: String
let title: String?
let coordinate: CLLocationCoordinate2D
let subtitle: String?
init?(id: String, dictionary: [String: AnyObject]){
self.id = id
title = dictionary["title"] as? String
subtitle = dictionary["subtitle"] as? String
guard let
coordinates = dictionary["coordinates"] as? [String: [String: Double]],
latitude = coordinates.values.first?["latitude"],
longitude = coordinates.values.first?["longitude"] else {
return nil
}
coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
super.init()
}
}
Now you have a failable initializer. If any of the values in the dictionary is not correct, the initializer returns nil. Otherwise, your values are all properly initialized.