swift - 如何将符合 Codable 协议(protocol)的枚举保存到 UserDefaults？

Question

跟进我之前的question :

我设法使我的枚举符合 Codable 协议(protocol)，实现了 init() 和 encode() 并且它似乎工作正常。

enum UserState {
    case LoggedIn(LoggedInState)
    case LoggedOut(LoggedOutState)
}

enum LoggedInState: String {
    case playing
    case paused
    case stopped
}

enum LoggedOutState: String {
    case Unregistered
    case Registered
}

extension UserState: Codable {
    enum CodingKeys: String, CodingKey {
        case loggedIn
        case loggedOut
    }

    enum CodingError: Error {
        case decoding(String)

    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        if let loggedIn = try? values.decode(String.self, forKey: .loggedIn) {
            self = .LoggedIn(LoggedInState(rawValue: loggedIn)!)
        }
        else if let loggedOut = try? values.decode(String.self, forKey: .loggedOut) {
            self = .LoggedOut(LoggedOutState(rawValue: loggedOut)!)
        }
        else {
            throw CodingError.decoding("Decoding failed")
        }
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)

        switch self {
        case let .LoggedIn(value):
            try container.encode(value.rawValue, forKey: .loggedIn)
        case let .LoggedOut(value):
            try container.encode(value.rawValue, forKey: .loggedOut)
        }
    }
}



class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let state = UserState.LoggedIn(.playing)
        UserDefaults.standard.set(state, forKey: "state")
    }
}

我的问题是我不知道如何将它保存到 UserDefaults。如果我像现在一样保存它，我会在运行应用程序时收到以下错误:

[User Defaults] Attempt to set a non-property-list object Codable.UserState.LoggedIn(Codable.LoggedInState.playing) as an NSUserDefaults/CFPreferences value for key state
2018-01-20 19:06:26.909349+0200 Codable[6291:789687]

Answer 1

来自 UserDefaults 引用:

A default object must be a property list—that is, an instance of (or for collections, a combination of instances of) NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. If you want to store any other type of object, you should typically archive it to create an instance of NSData.

所以你应该手动编码state并将其存储为数据:

if let encoded = try? JSONEncoder().encode(state) {
    UserDefaults.standard.set(encoded, forKey: "state")
}

然后，读回:

guard let data = UserDefaults.standard.data(forKey: "state") else { fatalError() }
if let saved = try? JSONDecoder().decode(UserState.self, from: data) {
    ...
}