在Swift中，可以将字符串转换为枚举吗？

如果我有一个用a，b，c，d的枚举，是否可以将字符串“ a”强制转换为枚举？

当然。枚举可以具有原始值。引用文档：

原始值可以是字符串，字符或任何整数或浮点数类型

—摘自：Apple Inc.“ Swift编程语言”。iBooks。https://itun.es/us/jEUH0.l，

因此，您可以使用如下代码：

enum StringEnum: String 
{
  case one = "one"
  case two = "two"
  case three = "three"
}

let anEnum = StringEnum(rawValue: "one")!

print("anEnum = \"\(anEnum.rawValue)\"")

注意：在每种情况下，您无需写=“ one”等。默认的字符串值与案例名称相同，因此调用.rawValue只会返回一个字符串

编辑

如果您需要字符串值来包含诸如空格之类的无效内容，这些值不能作为case值的一部分，那么您需要显式设置字符串。所以，

enum StringEnum: String 
{
  case one
  case two
  case three
}

let anEnum = StringEnum.one
print("anEnum = \"\(anEnum)\"")

给

anEnum =“一个”

但是，如果要case one显示“值一”，则需要提供字符串值：

enum StringEnum: String 
{
  case one   = "value one"
  case two   = "value two"
  case three = "value three"
}

所有你需要的是：

enum Foo: String {
   case a, b, c, d
}

let a = Foo(rawValue: "a")
assert(a == Foo.a)

let 💩 = Foo(rawValue: "💩")
assert(💩 == nil)

在Swift 4.2中，CaseIterable协议可用于具有rawValues的枚举，但是字符串应与枚举的大小写标签匹配：

enum MyCode : String, CaseIterable {

    case one   = "uno"
    case two   = "dos"
    case three = "tres"

    static func withLabel(_ label: String) -> MyCode? {
        return self.allCases.first{ "\($0)" == label }
    }
}

用法：

print(MyCode.withLabel("one")) // Optional(MyCode.one)
print(MyCode(rawValue: "uno"))  // Optional(MyCode.one)

如果是Int类型的枚举，则可以这样做：

enum MenuItem: Int {
    case One = 0, Two, Three, Four, Five //... as much as needs

    static func enumFromString(string:String) -> MenuItem? {
        var i = 0
        while let item = MenuItem(rawValue: i) {
            if String(item) == string { return item }
            i += 1
        }
        return nil
    }
}

并使用：

let string = "Two"
if let item = MenuItem.enumFromString(string) {
    //in this case item = 1 
    //your code
} 

扩展邓肯C的答案

extension StringEnum: StringLiteralConvertible {

    init(stringLiteral value: String){
        self.init(rawValue: value)!
    }

    init(extendedGraphemeClusterLiteral value: String) {
        self.init(stringLiteral: value)
    }

    init(unicodeScalarLiteral value: String) {
        self.init(stringLiteral: value)
    }
}

Swift 4.2：

public enum PaymentPlatform: String, CaseIterable {
    case visa = "Visa card"
    case masterCard = "Master card"
    case cod = "Cod"

    var nameEnum: String {
        return Mirror(reflecting: self).children.first?.label ?? String(describing: self)
    }

    func byName(name: String) -> PaymentPlatform {
        return PaymentPlatform.allCases.first(where: {$0.nameEnum.elementsEqual(name)}) ?? .cod
    }
}

对于Int枚举及其字符串表示形式，我将枚举声明如下：

enum OrderState: Int16, CustomStringConvertible {

    case waiting = 1
    case inKitchen = 2
    case ready = 3

    var description: String {
        switch self {
        case .waiting:
            return "Waiting"
        case .inKitchen:
            return "InKitchen"
        case .ready:
            return "Ready"
        }
    }

    static func initialize(stringValue: String)-> OrderState? {
        switch stringValue {
        case OrderState.waiting.description:
            return OrderState.waiting
        case OrderState.inKitchen.description:
            return OrderState.inKitchen
        case OrderState.ready.description:
            return OrderState.ready

        default:
            return nil
        }
    }
}

用法：

order.orderState = OrderState.waiting.rawValue

let orderState = OrderState.init(rawValue: order.orderState)
let orderStateStr = orderState?.description ?? ""
print("orderStateStr = \(orderStateStr)")