This code demonstrate archive and unarchive objects derived from a certain class and its descendants using NSObject and NSCoding

archive-unarchive-2.swift

/*
	This sample code shows the problem of archive and unarchive abstruct objects. Please see `TODO` keyword
	and make this Contents class to save and load shape objects.

	CASE: All target objects are based on NSObject with NSCoding to archive and unarchive Shape desendant class objects

	file: archive-unarchive-1.swift
	https://gist.github.com/codelynx/428b27b3cfd58b8c7382346f1a4bc415
	
*/

import Foundation
import CoreGraphics

protocol Shape: NSObject, NSCoding {
	init?(coder: NSCoder)
	func encode(with coder: NSCoder)
}

class Circle: NSObject, Shape {
	var center: CGPoint
	var radius: CGFloat
	init(center: CGPoint, radius: CGFloat) {
		self.center = center
		self.radius = radius
		super.init()
	}
	required init?(coder: NSCoder) {
		self.center = coder.decodeObject(forKey: "center") as! CGPoint
		self.radius = coder.decodeObject(forKey: "radius") as! CGFloat
		super.init()
	}
	func encode(with coder: NSCoder) {
		coder.encode(self.center, forKey: "center")
		coder.encode(self.radius, forKey: "radius")
	}
	override var description: String { "{Circle: \(self.center)-\(self.radius)}" }
}

class Rectangle: NSObject, Shape {
	var origin: CGPoint
	var size: CGSize
	init(origin: CGPoint, size: CGSize) {
		self.origin = origin
		self.size = size
		super.init()
	}
	required init?(coder: NSCoder) {
		self.origin = coder.decodeObject(forKey: "origin") as! CGPoint
		self.size = coder.decodeObject(forKey: "size") as! CGSize
		super.init()
	}
	func encode(with coder: NSCoder) {
		coder.encode(self.origin, forKey: "origin")
		coder.encode(self.size, forKey: "size")
	}
	override var description: String { "{Rectangle: origin=\(self.origin), size=\(self.size)}" }
}

class RoundedRectangle: Rectangle {
	var cornerRadius: CGFloat
	init(origin: CGPoint, size: CGSize, radius: CGFloat) {
		self.cornerRadius = radius
		super.init(origin: origin, size: size)
	}
	required init?(coder: NSCoder) {
		self.cornerRadius = coder.decodeObject(forKey: "cornerRadius") as! CGFloat
		super.init(coder: coder)
	}
	override func encode(with coder: NSCoder) {
		coder.encode(self.cornerRadius, forKey: "cornerRadius")
		super.encode(with: coder)
	}
	override var description: String { "{RoundedRectangle: origin=\(self.origin), size=\(self.size), cornerRadius=\(self.cornerRadius)}" }
}

class Contents: NSObject, NSCoding {
	var shapes: [Shape]
	init(shapes: [Shape]) {
		self.shapes = shapes
	}
	required init?(coder: NSCoder) {
		self.shapes = coder.decodeObject(forKey: "shapes") as! [Shape]
	}
	func encode(with coder: NSCoder) {
		coder.encode(self.shapes, forKey: "shapes")
	}
	override var description: String { "{Contents:" + self.shapes.map { $0.description }.joined(separator: ",") + "}" }
}

let contents = Contents(shapes: [
	Circle(center: CGPoint(x: 10, y: 20), radius: 30),
	Rectangle(origin: CGPoint(x: 40, y: 50), size: CGSize(width: 60, height: 70)),
	RoundedRectangle(origin: CGPoint(x: 100, y: 110), size: CGSize(width: 120, height: 130), radius: 5)
])

let data = try! NSKeyedArchiver.archivedData(withRootObject: contents, requiringSecureCoding: false)
let object = try! NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data)

switch object {
case let circle as Circle:
	print("circle:", circle.center, circle.radius)
case let rectangle as RoundedRectangle:
	print("rounded rectangle:", rectangle.origin, rectangle.size)
case let rectangle as Rectangle:
	print("rectangle:", rectangle.origin, rectangle.size)
case let contents as Contents:
	print("contents:", contents.shapes.map { $0.description })
default:
	print("unexpected object")
}