如果我有一份使用原始Integer值的枚举:
enum City: Int {
case Melbourne = 1, Chelyabinsk, Bursa
}
let city = City.Melbourne
我如何将city的值转换为字符串 Melbourne？语言中是否有此类类型名称内省的功能？
类似这样的操作（以下代码无法运行）：
println("Your city is \(city.magicFunction)")
> Your city is Melbourne
print(_:)默认打印类型名称和枚举情况，或使用String的init(_:)初始化器或字符串插值语法转换为String。因此，对于您的示例：enum City: Int {
case Melbourne = 1, Chelyabinsk, Bursa
}
let city = City.Melbourne
print(city)
// prints "Melbourne"
let cityName = "\(city)" // or `let cityName = String(city)`
// cityName contains "Melbourne"
debugPrint(city)
// prints "App.City.Melbourne" (or similar, depending on the full scope)
let cityDebugName = String(reflecting: city)
// cityDebugName contains "App.City.Melbourne"
extension City: CustomStringConvertible {
var description: String {
return "City \(rawValue)"
}
}
print(city)
// prints "City 1"
extension City: CustomDebugStringConvertible {
var debugDescription: String {
return "City (rawValue: \(rawValue))"
}
}
debugPrint(city)
// prints "City (rawValue: 1)"
extension String {
/// Initialize `self` with the textual representation of `instance`.
///
/// * If `T` conforms to `Streamable`, the result is obtained by
/// calling `instance.writeTo(s)` on an empty string s.
/// * Otherwise, if `T` conforms to `CustomStringConvertible`, the
/// result is `instance`'s `description`
/// * Otherwise, if `T` conforms to `CustomDebugStringConvertible`,
/// the result is `instance`'s `debugDescription`
/// * Otherwise, an unspecified result is supplied automatically by
/// the Swift standard library.
///
/// - SeeAlso: `String.init<T>(reflecting: T)`
public init<T>(_ instance: T)
/// Initialize `self` with a detailed textual representation of
/// `subject`, suitable for debugging.
///
/// * If `T` conforms to `CustomDebugStringConvertible`, the result
/// is `subject`'s `debugDescription`.
///
/// * Otherwise, if `T` conforms to `CustomStringConvertible`, the result
/// is `subject`'s `description`.
///
/// * Otherwise, if `T` conforms to `Streamable`, the result is
/// obtained by calling `subject.writeTo(s)` on an empty string s.
///
/// * Otherwise, an unspecified result is supplied automatically by
/// the Swift standard library.
///
/// - SeeAlso: `String.init<T>(T)`
public init<T>(reflecting subject: T)
}
查看发布说明了解有关此更改的信息。
目前枚举案例没有自省。您将不得不手动声明它们：
enum City: String, CustomStringConvertible {
case Melbourne = "Melbourne"
case Chelyabinsk = "Chelyabinsk"
case Bursa = "Bursa"
var description: String {
get {
return self.rawValue
}
}
}
如果您需要原始类型为Int，您将不得不自己进行切换：
enum City: Int, CustomStringConvertible {
case Melbourne = 1, Chelyabinsk, Bursa
var description: String {
get {
switch self {
case .Melbourne:
return "Melbourne"
case .Chelyabinsk:
return "Chelyabinsk"
case .Bursa:
return "Bursa"
}
}
}
}
get { ... } 部分。 - iosdudeenum City：String，CustomStringConvertible {。作为CSC协议的一部分，您还需要将属性更改为public，例如：public var description：String {。 - Goffredo/**
* The name of the enumeration (as written in case).
*/
var name: String {
get { return String(describing: self) }
}
/**
* The full name of the enumeration
* (the name of the enum plus dot plus the name as written in case).
*/
var description: String {
get { return String(reflecting: self) }
}
enum City: Int {
case Melbourne = 1, Chelyabinsk, Bursa
var name: String {
get { return String(describing: self) }
}
var description: String {
get { return String(reflecting: self) }
}
}
let city = City.Melbourne
print(city.name)
// prints "Melbourne"
print(city.description)
// prints "City.Melbourne"
如果你想为所有的枚举提供这个功能，你可以将它作为扩展。
/**
* Extend all enums with a simple method to derive their names.
*/
extension RawRepresentable where RawValue: Any {
/**
* The name of the enumeration (as written in case).
*/
var name: String {
get { return String(describing: self) }
}
/**
* The full name of the enumeration
* (the name of the enum plus dot plus the name as written in case).
*/
var description: String {
get { return String(reflecting: self) }
}
}
这只适用于Swift枚举。
String(describing:)初始化程序可用于返回具有非字符串rawValues的枚举的案例标签名称：enum Numbers: Int {
case one = 1
case two = 2
}
let one = String(describing: Numbers.one) // "one"
let two = String(describing: Numbers.two) // "two"
@objc修饰符，则不起作用：
为Objective-C类型生成的Swift接口有时不包括@objc修饰符。这些枚举在Objective-C中定义，因此不能像上面那样工作。对于Objective-C的enum，目前唯一的方法似乎是，例如，使用CustomStringConvertible扩展枚举，最终得到类似以下代码：
对于Objective-C的enum，目前唯一的方法似乎是，例如，使用CustomStringConvertible扩展枚举，最终得到类似以下代码：
extension UIDeviceBatteryState: CustomStringConvertible {
public var description: String {
switch self {
case .Unknown:
return "Unknown"
case .Unplugged:
return "Unplugged"
case .Charging:
return "Charging"
case .Full:
return "Full"
}
}
}
然后将 enum 强制转换为 String:
String(UIDevice.currentDevice().batteryState)
除了Swift 2.2中枚举类型支持String(...) (CustomStringConvertible)之外，它们还具有相对瑕疵的反射支持。对于带有关联值的枚举情况，可以使用反射获取枚举情况的标签：
enum City {
case Melbourne(String)
case Chelyabinsk
case Bursa
var label:String? {
let mirror = Mirror(reflecting: self)
return mirror.children.first?.label
}
}
print(City.Melbourne("Foobar").label) // prints out "Melbourne"
所谓"被破坏"，仅仅指对于那些比较"简单"的枚举类型，上述基于反射的label计算属性只会返回nil（唉哟）。
print(City.Chelyabinsk.label) // prints out nil
据说自Swift 3以后，反射技术的情况应该会有所改善。不过目前的解决方法是使用另一个答案中建议的String(…)：
print(String(City.Chelyabinsk)) // prints out Cheylabinsk
var label:String { let mirror = Mirror(reflecting: self); if let label = mirror.children.first?.label { return label } else { return String(describing:self) } } - David James现在，Swift拥有所谓的隐式分配原始值。基本上，如果您没有为每个case指定原始值，并且枚举类型为String，则它会推断出该case的原始值本身是字符串格式。继续尝试一下吧。
enum City: String {
case Melbourne, Chelyabinsk, Bursa
}
let city = City.Melbourne.rawValue
// city is "Melbourne"
我偶然看到了这个问题，并想分享一个简单的方法来创建所提到的magicFunction。
enum City: Int {
case Melbourne = 1, Chelyabinsk, Bursa
func magicFunction() -> String {
return "\(self)"
}
}
let city = City.Melbourne
city.magicFunction() //prints Melbourne
这真是令人失望。
对于那些需要使用编译器已经完全知道拼写的名称（但拒绝访问的情况——谢谢Swift团队！！），但又不想或不能将String作为枚举基础的情况，有一种冗长、繁琐的替代方法如下：
enum ViewType : Int, Printable {
case Title
case Buttons
case View
static let all = [Title, Buttons, View]
static let strings = ["Title", "Buttons", "View"]
func string() -> String {
return ViewType.strings[self.rawValue]
}
var description:String {
get {
return string()
}
}
}
let elementType = ViewType.Title
let column = Column.Collections
let row = 0
println("fetching element \(elementType), column: \(column.string()), row: \(row)")
你将得到期望的结果（列的代码类似，但未显示）
fetching element Title, column: Collections, row: 0
对于Swift：
extension UIDeviceBatteryState: CustomStringConvertible {
public var description: String {
switch self {
case .unknown:
return "unknown"
case .unplugged:
return "unplugged"
case .charging:
return "charging"
case .full:
return "full"
}
}
}
self.batteryState.description
print(enum)来获取枚举类型的字符串值，你可以使用String(enum)。 - KametrixomlocationManager didChangeAuthorizationStatus委托回调中打印(Objective C)CLAuthorizationStatus枚举的值，那么你需要定义一个协议扩展。例如：extension CLAuthorizationStatus: CustomStringConvertable { public var description: String { switch self { case .AuthorizedAlways: return "AuthorizedAlways" <etc> } } }- 一旦你完成了这个步骤，它应该按照你的预期工作：print("Auth status: (\status))”。 - Goffredo