Tell me about encoding and decoding data in UserDefaults.

UserDefaults stores data in key-value pairs. For custom data types not directly supported (String, Int, Bool, Data, Array, Dictionary), encoding/decoding is required. The Codable protocol is used, which combines Encodable and Decodable.

Example of encoding a custom type:

struct User: Codable {
    let name: String
    let age: Int
}

let user = User(name: "Ivan", age: 30)

Using PropertyListEncoder and PropertyListDecoder, you can encode/decode Codable objects into Data for storage in UserDefaults.

Encoding:

let encoder = PropertyListEncoder()
if let encoded = try? encoder.encode(user) {
    UserDefaults.standard.set(encoded, forKey: "currentUser")
}

Decoding:

if let savedData = UserDefaults.standard.data(forKey: "currentUser") {
    let decoder = PropertyListDecoder()
    if let loadedUser = try? decoder.decode(User.self, from: savedData) {
        print("Loaded user: \(loadedUser.name), age: \(loadedUser.age)")
    }
}

An alternative (less preferred for new projects) is using NSCoding with inheritance from NSObject.

Comparison of methods:

Method	Protocol/Class	Support for Value/Reference Types	Required Methods	Ease of Use
Codable	Codable (Encodable, Decodable)	Value & Reference	Automatic synthesis when conditions are met	High
NSCoding	NSCoding	Reference (requires NSObject)	init(coder:), encode(with:)	Medium

Codable is the modern and recommended approach due to its simplicity and automatic synthesis. NSCoding may be required for legacy code support.