如何（优雅地）将 Swift 枚举与相关值保持一致——或者我应该避免使用它们吗？答案

【问题标题】：How to (elegantly) persist Swift enum with associated values - or should I avoid them?如何（优雅地）将 Swift 枚举与相关值保持一致——或者我应该避免使用它们吗？
【发布时间】：2016-06-01 09:20:52
【问题描述】：

我被 Swift 的出色表现力所吸引，并打算为每个案例使用一个带有关联值的枚举，例如：

enum PlayerStatus {
    case Playing (league: Int, position: Int)
    case NotPlaying (ReasonNotPlaying, LastPlayed)
}

enum ReasonNotPlaying {
    case Injured
    case Away
    case DidntPlay
    case Left
}

struct LastPlayed {
    let year: Int
    let position: Int
}

class Player {

    var firstName: String = ""
    var surname: String = ""
    //  etc

    var status: PlayerStatus? = nil
}

但是，我需要 PERSIST 包含枚举的 Player 类，Realm 和 CoreData 都没有任何简单的机制来执行此操作 - 可能是因为具有关联值的枚举在 Objective-C 中不可用（或者，在Realm，在 Android 中？）

我误解了枚举吗？我的例子可能不清楚吗？或者我怎样才能简洁地持久化枚举？

有什么建议吗？

【问题讨论】：

标签： swift core-data enums realm

【解决方案1】：

你是对的。目前，Realm 不支持存储 Enum。因此，没有简单的方法可以直接存储具有关联值的 Enum。

我建议的解决方法如下：

将枚举值提取到属性。然后覆盖枚举的 setter/getter 以将枚举值转换为每个 set/get 的属性。看起来太复杂了，其实用法很简单，正常设置/获取status属性即可。

enum PlayerStatus {
    case Playing (league: Int, position: Int)
    case NotPlaying (ReasonNotPlaying, LastPlayed)
}

enum ReasonNotPlaying: String {
    case Injured
    case Away
    case DidntPlay
    case Left
}

struct LastPlayed {
    let year: Int
    let position: Int
}

class Player: Object {
    dynamic var firstName: String = ""
    dynamic var surname: String = ""
    //  etc

    private let playingLeague = RealmOptional<Int>()
    private let playingPosition = RealmOptional<Int>()

    private dynamic var reasonNotPlaying: String? = nil

    private let lastPlayedYear = RealmOptional<Int>()
    private let lastPlayedPosition = RealmOptional<Int>()

    var status: PlayerStatus? {
        get {
            if let league = playingLeague.value,
                let position = playingPosition.value {
                return PlayerStatus.Playing(league: league, position: position)
            } else if let year = lastPlayedYear.value,
                let position = lastPlayedPosition.value,
                let reason = reasonNotPlaying {
                return PlayerStatus.NotPlaying(ReasonNotPlaying(rawValue: reason)!,
                                               LastPlayed(year: year, position: position))
            }
            return nil
        }
        set {
            if let newValue = newValue {
                switch newValue {
                case let .Playing(league, position):
                    playingLeague.value = league
                    playingPosition.value = position

                    reasonNotPlaying = nil
                    lastPlayedYear.value = nil
                    lastPlayedPosition.value = nil
                case let .NotPlaying(reason, lastPlayed):
                    playingLeague.value = nil
                    playingPosition.value = nil

                    reasonNotPlaying = reason.rawValue
                    lastPlayedYear.value = lastPlayed.year
                    lastPlayedPosition.value = lastPlayed.position
                }
            } else {
                playingLeague.value = nil
                playingPosition.value = nil

                reasonNotPlaying = nil
                lastPlayedYear.value = nil
                lastPlayedPosition.value = nil
            }
        }
    }

    override static func ignoredProperties() -> [String] {
        return ["status"]
    }
}

【讨论】：