This is an example of how to use UserDefaults inside a ViewModel. We should not store more than 500KB of data in UserDefaults

UserDefaultsExample.swift

import Foundation

struct Card: Identifiable, Codable {
    var id = UUID()
    let prompt: String
    let answer: String
}

@MainActor class ViewModel: ObservableObject {
    @Published var cards = [Card]()
    
    init() {
        loadData()
    }
    
    func loadData() {
        if let data = UserDefaults.standard.data(forKey: "Cards") {
            if let decoded = try? JSONDecoder().decode([Card].self, from: data) {
                cards = decoded
            }
        }
    }
    
    func saveData() {
        if let data = try? JSONEncoder().encode(cards) {
            UserDefaults.standard.set(data, forKey: "Cards")
        }
    }
}