How to save a struct with NSCoding - swift

Question

How can I save my struct with NSCoding so that it doesn´t change even if the user
closes the app? I would appreciate it if you could also show me how to implement the missing code correctly.
UPDATE with two new functions below:
Here is my code:
struct RandomItems: Codable
{
var items : [String]
var seen = 0
init(items:[String], seen: Int)
{
self.items = items
self.seen = seen
}
init(_ items:[String])
{ self.init(items: items, seen: 0) }
mutating func next() -> String
{
let index = Int(arc4random_uniform(UInt32(items.count - seen)))
let item = items.remove(at:index)
items.append(item)
seen = (seen + 1) % items.count
return item
}
func toPropertyList() -> [String: Any] {
return [
"items": items,
"seen": seen
]
}
}
override func viewWillDisappear(_ animated: Bool) {
UserDefaults.standard.set(try? PropertyListEncoder().encode(quotes), forKey:"quote2")
}
override func viewDidAppear(_ animated: Bool) {
if let data = UserDefaults.standard.value(forKey:"quote2") as? Data {
let quote3 = try? PropertyListDecoder().decode(Array<RandomItems>.self, from: data)
}
}
}
extension QuotesViewController.RandomItems {
init?(propertyList: [String: Any]) {
return nil
}
}
How can I make sure the whole Array is covered here?

Answer 1

For structs you should be using the new Codable protocol. It is available since swift 4 and is highly recommended.
struct RandomItems: Codable
{
var items: [String]
var seen = 0
}
extension RandomItems {
init?(propertyList: [String: Any]) {
...
}
}
// Example usage
let a = RandomItems(items: ["hello"], seen: 2)
let data: Data = try! JSONEncoder().encode(a)
UserDefaults.standard.set(data, forKey: "MyKey") // Save data to disk
// some time passes
let data2: Data = UserDefaults.standard.data(forKey: "MyKey")! // fetch data from disk
let b = try! JSONDecoder().decode(RandomItems.self, from: data2)
Update
It looks like the Original Poster is nesting the struct inside of another class. Here is another example where there struct is nested.
class QuotesViewController: UIViewController {
struct RandomItems: Codable
{
var items: [String]
var seen = 0
}
}
extension QuotesViewController.RandomItems {
init(_ items:[String])
{ self.items = items }
init?(propertyList: [String: Any]) {
guard let items = propertyList["items"] as? [String] else { return nil }
guard let seen = propertyList["seen"] as? Int else { return nil }
self.items = items
self.seen = seen
}
}
// example usage
let a = QuotesViewController.RandomItems(items: ["hello"], seen: 2)
let data: Data = try! JSONEncoder().encode(a)
UserDefaults.standard.set(data, forKey: "MyKey") // Save data to disk
// some time passes
let data2: Data = UserDefaults.standard.data(forKey: "MyKey")! // fetch data from disk
let b = try! JSONDecoder().decode(QuotesViewController.RandomItems.self, from: data2)