背景
我正在尝试使用 NSCoding 协议对字符串样式枚举进行编码，但在与字符串之间转换和返回时遇到错误。
我在解码和编码时遇到以下错误：
字符串无法转换为 Stage
额外参数 ForKey：在调用中
Code
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
}
// ...
}
您需要将枚举与原始值相互转换。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代替as!:
self.stage = Stage(rawValue: (aDecoder.decodeObjectForKey( "stage" ) as String)) ?? .DisplayAll
Swift 1.0（Xcode 6.0）使用toRaw() and fromRaw()像这样：
self.stage = Stage.fromRaw(aDecoder.decodeObjectForKey( "stage" ) as String) ?? .DisplayAll
aCoder.encodeObject( self.stage.toRaw(), forKey:"stage" )
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