How to save a swift struct to file - ios

Question

I want to use structs for the (very simple) model of my app.
However NSKeyedArchiver only accepts objects (extending NSObjects).
Is there any good way to save a struct to a file?

Answer 1

A very simple approach I used sometimes. The quantity of code you need to write is no more then in the class/NSCoding scenario.
First of all import the great SwiftyJSON lib.
Let's start with a simple struct
struct Starship {
let name: String
let warpSpeed: Bool
let captain: String?
init(name: String, warpSpeed: Bool, captain: String? = nil) {
self.name = name
self.warpSpeed = warpSpeed
self.captain = captain
}
}
Let's make it convertible to/from a JSON
struct Starship {
let name: String
let warpSpeed: Bool
let captain: String?
init(name: String, warpSpeed: Bool, captain: String? = nil) {
self.name = name
self.warpSpeed = warpSpeed
self.captain = captain
}
init?(json: JSON) {
guard let
name = json["name"].string,
warpSpeed = json["warpSpeed"].bool
else { return nil }
self.name = name
self.warpSpeed = warpSpeed
self.captain = json["captain"].string
}
var asJSON: JSON {
var json: JSON = [:]
json["name"].string = name
json["warpSpeed"].bool = warpSpeed
json["captain"].string = captain
return json
}
}
That's it. Let's use it
let enterprise = Starship(name: "Enteriprise D", warpSpeed: true, captain: "JeanLuc Picard")
let json = enterprise.asJSON
let data = try! json.rawData()
// save data to file and reload it
let newJson = JSON(data: data)
let ship = Starship(json: newJson)
ship?.name // "Enterprise D"

Answer 2

Updated solution for Swift 5+
No need to import anything
Make your struct codable
struct Starship: Codable { // Add this
let name: String
let warpSpeed: Bool
let captain: String?
init(name: String, warpSpeed: Bool, captain: String? = nil) {
self.name = name
self.warpSpeed = warpSpeed
self.captain = captain
}
}
Functions to read from and write to file
var data: Starship
func readFromFile(filePathURL: URL) throws {
let readData = try Data(contentsOf: filePathURL)
self.data = try JSONDecoder().decode(Starship.self, from: readData)
}
func writeToFile(filePathURL: URL) throws {
let jsonData = try JSONEncoder().encode(self.data)
try jsonData.write(to: filePathURL)
}