swift - 如何在 swift 中使用 NSCoder 对枚举进行编码？

Question

背景

我正在尝试使用 NSCoding 协议对字符串样式的枚举进行编码，但是在与 String 之间进行转换时遇到了错误。

解码和编码时出现以下错误：

字符串不能转换为 Stage

额外参数 ForKey：在调用中

代码

    enum Stage : String
    {
        case DisplayAll    = "Display All"
        case HideQuarter   = "Hide Quarter"
        case HideHalf      = "Hide Half"
        case HideTwoThirds = "Hide Two Thirds"
        case HideAll       = "Hide All"
    }

    class AppState : NSCoding, NSObject
    {
        var idx   = 0
        var stage = Stage.DisplayAll

        override init() {}

        required init(coder aDecoder: NSCoder) {
            self.idx   = aDecoder.decodeIntegerForKey( "idx"   )
            self.stage = aDecoder.decodeObjectForKey(  "stage" ) as String    // ERROR
        }

        func encodeWithCoder(aCoder: NSCoder) {
            aCoder.encodeInteger( self.idx,             forKey:"idx"   )
            aCoder.encodeObject(  self.stage as String, forKey:"stage" )  // ERROR
        }

    // ...

    }

Answer 1

您需要将枚举与原始值进行转换。在 Swift 1.2 (Xcode 6.3) 中，这看起来像这样：

class AppState : NSObject, NSCoding
{
    var idx   = 0
    var stage = Stage.DisplayAll

    override init() {}

    required init(coder aDecoder: NSCoder) {
        self.idx   = aDecoder.decodeIntegerForKey( "idx" )
        self.stage = Stage(rawValue: (aDecoder.decodeObjectForKey( "stage" ) as! String)) ?? .DisplayAll
    }

    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encodeInteger( self.idx, forKey:"idx" )
        aCoder.encodeObject(  self.stage.rawValue, forKey:"stage" )
    }

    // ...

}

Swift 1.1 (Xcode 6.1)，使用as而不是as!：

    self.stage = Stage(rawValue: (aDecoder.decodeObjectForKey( "stage" ) as String)) ?? .DisplayAll

Swift 1.0 (Xcode 6.0) 使用toRaw()和fromRaw()这样的：

    self.stage = Stage.fromRaw(aDecoder.decodeObjectForKey( "stage" ) as String) ?? .DisplayAll

    aCoder.encodeObject( self.stage.toRaw(), forKey:"stage" )

Answer 2

这是Swift 4.2的解决方案。如其他答案所述，问题在于您尝试stage使用解码的字符串直接分配变量，并尝试将stage变量强制转换为方法中的字符串encodeWithCoder。您需要改用原始值。

enum Stage: String {
    case DisplayAll = "Display All"
    case HideQuarter = "Hide Quarter"
    case HideHalf = "Hide Half"
    case HideTwoThirds = "Hide Two Thirds"
    case HideAll = "Hide All"
}

class AppState: NSCoding, NSObject {
    var idx = 0
    var stage = Stage.DisplayAll

    override init() {}

    required init(coder aDecoder: NSCoder) {
        self.idx = aDecoder.decodeInteger(forKey: "idx")
        self.stage = Stage(rawValue: aDecoder.decodeObject(forKey: "stage") as String)
    }

    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encode(self.idx, forKey:"idx")
        aCoder.encode(self.stage.rawValue, forKey:"stage")
    }

    // ...

}

Answer 3

Xcode 6.3、Swift 1.2 的更新：

self.stage = Stage(rawValue: aDecoder.decodeObjectForKey("stage") as! String) ?? .DisplayAll

注意as!