struct MyData: Codable { var int: Int } do { let myData = MyData(int: 1) let encoder = JSONEncoder() let encoded = try encoder.encode(myData) UserDefaults.standard.setValue(encoded, forKey: "key") let saved = UserDefaults.standard.value(forKey: "key") as! Data let decoder = JSONDecoder() let decodedMyData = try decoder.decode(MyData.self, from: saved) // MyData(int: 1) } catch { print(error) } 使い方だいたいこんな感じです