Saving a Codable Struct to UserDefaults with Swift

Question

I am trying to encode a struct

struct Configuration : Encodable, Decodable {
    private enum CodingKeys : String, CodingKey {
        case title = "title"
        case contents = "contents"
    }
    var title : String?
    var contents: [[Int]]?
}

into JSON to store in a local key of UserDefaults.standard. I have the following code:

let jsonString = Configuration(title: nameField.text, contents: newContents)
let info = ["row" as String: jsonString as Configuration]
print("jsonString = \(jsonString)")
//trying to save object
let defaults = UserDefaults.standard
let recode = try! JSONEncoder().encode(jsonString)
defaults.set(recode, forKey: "simulationConfiguration")
//end of saving local

The print returns:

jsonString = Configuration(title: Optional("config"), contents: Optional([[4, 5], [5, 5], [6, 5]]))

so I believe I am creating the object correctly. However, when I try and retrieve the key the next time I run the simulator I get nothing. I put the following in AppDelegate and it always returns No Config.

let defaults = UserDefaults.standard
        let config = defaults.string(forKey: "simulationConfiguration") ?? "No Config"
        print("from app delegate = \(config.description)")

Any ideas? Thanks

Answer 1

Here you are saving a Data value (which is correct)

defaults.set(recode, forKey: "simulationConfiguration")

But here you are reading a String

defaults.string(forKey: "simulationConfiguration")

You cannot save Data, read String and expect it to work.

Let's fix your code

First of all you don't need to manually specify the Coding Keys. So your struct become simply this

struct Configuration : Codable {
    var title : String?
    var contents: [[Int]]?
}

Saving

Now here's the code for saving it

let configuration = Configuration(title: "test title", contents: [[1, 2, 3]])
if let data = try? JSONEncoder().encode(configuration) {
    UserDefaults.standard.set(data, forKey: "simulationConfiguration")
}

Loading

And here's the code for reading it

if
    let data = UserDefaults.standard.value(forKey: "simulationConfiguration") as? Data,
    let configuration = try? JSONDecoder().decode(Configuration.self, from: data) {
    print(configuration)
}