无论枚举情况如何，如何获得快速枚举的相关值

Question

我有一个对象FormField有两个属性：一个字符串name和一个可以接受任何类型的value - 因此我已经使它成为Any! 。 但是，我在一个单独的问题中被告知要使用带有关联值而不是Any!的枚举Any! 。

enum Value {
    case Text(String!)
    case CoreDataObject(NSManagedObject!)
}

class FormField {
    var name: String
    var value: Value?
    // initializers...
}

然而，这种方法使得检查无效非常冗长。 如果我想显示表单中所有缺少字段的警报视图，我将不得不对switch语句中的每个案例重复nil检查：

for field in self.fields {
    if let value = field.value {
        switch value {
        case .Text(let text):
            if text == nil {
                missingFields.append(field.name)
            }
        case .CoreDataObject(let object):
            if object == nil {
                missingFields.append(field.name)
            }
        }
    }
}

无论类型如何，是否有更短的方式来访问枚举的相关值？ 如果我使FormField.value成为Any! 上面的代码就像下面这样简单：

for field in self.fields {
    if field.value == nil {
        missingFields.append(field.name)
    }
}

Answer 1

在enum定义一个方法isMissing() - 只写一次。 然后你几乎完全得到你喜欢的东西：

for field in self.fields {
    if field.value.isMissing() {
        missingFields.append(field.name)
    }
}

它看起来像这样（来自Swift Interpreter）：

  1> class Foo {}
   >
  2> enum Value { 
  3.     case One(Foo!) 
  4.     case Two(Foo!) 
  5.      
  6.     func isMissing () -> Bool { 
  7.         switch self { 
  8.         case let .One(foo): return foo == nil 
  9.         case let .Two(foo): return foo == nil 
 10.         } 
 11.     } 
 12. }    
 13> let aVal = Value.One(nil)
aVal: Value = One {
  One = nil
}
 14> aVal.isMissing()
$R0: Bool = true

Answer 2

使用Swift 2，可以使用反射获得相关值。

为了更容易，只需将下面的代码添加到项目中，并使用EVAssociated协议扩展枚举。

    public protocol EVAssociated {
    }

    public extension EVAssociated {
        public var associated: (label:String, value: Any?) {
            get {
                let mirror = Mirror(reflecting: self)
                if let associated = mirror.children.first {
                    return (associated.label!, associated.value)
                }
                print("WARNING: Enum option of \(self) does not have an associated value")
                return ("\(self)", nil)
            }
        }
    }

然后，您可以使用以下代码访问.asociated值：

    class EVReflectionTests: XCTestCase {
            func testEnumAssociatedValues() {
                let parameters:[EVAssociated] = [usersParameters.number(19),
usersParameters.authors_only(false)]
            let y = WordPressRequestConvertible.MeLikes("XX", Dictionary(associated: parameters))
            // Now just extract the label and associated values from this enum
            let label = y.associated.label
            let (token, param) = y.associated.value as! (String, [String:Any]?)

            XCTAssertEqual("MeLikes", label, "The label of the enum should be MeLikes")
            XCTAssertEqual("XX", token, "The token associated value of the enum should be XX")
            XCTAssertEqual(19, param?["number"] as? Int, "The number param associated value of the enum should be 19")
            XCTAssertEqual(false, param?["authors_only"] as? Bool, "The authors_only param associated value of the enum should be false")

            print("\(label) = {token = \(token), params = \(param)")
        }
    }

    // See http://github.com/evermeer/EVWordPressAPI for a full functional usage of associated values
    enum WordPressRequestConvertible: EVAssociated {
        case Users(String, Dictionary<String, Any>?)
        case Suggest(String, Dictionary<String, Any>?)
        case Me(String, Dictionary<String, Any>?)
        case MeLikes(String, Dictionary<String, Any>?)
        case Shortcodes(String, Dictionary<String, Any>?)
    }

    public enum usersParameters: EVAssociated {
        case context(String)
        case http_envelope(Bool)
        case pretty(Bool)
        case meta(String)
        case fields(String)
        case callback(String)
        case number(Int)
        case offset(Int)
        case order(String)
        case order_by(String)
        case authors_only(Bool)
        case type(String)
    }

上面的代码现在可以作为cocoapod susbspec在https://github.com/evermeer/Stuff#enum上获得。它还有一个其他很好的枚举扩展，用于枚举所有枚举值。

Answer 3

如果相关值对于所有枚举案例具有相同类型，则以下方法可能有所帮助。

enum Value {
    case text(NSString!), two(NSString!), three(NSString!) // This could be any other type including AnyClass
}

// Emulating "fields" datastruct for demo purposes (as if we had struct with properties).
typealias Field = (en: Value, fieldName: String)
let fields: [Field] = [(.text(nil),"f1"), (.two(nil), "f2"), (.three("Hey"), "f3")] // this is analog of "fields"

let arrayOfFieldNamesWithEmptyEnums: [String] = fields.compactMap({
    switch $0.en {
    case let .text(foo), let .two(foo), let .three(foo): if foo == nil { return $0.fieldName } else { return nil }}
})
print("arrayOfFieldNamesWithEmptyEnums \(arrayOfFieldNamesWithEmptyEnums)")

可以类似地获得许多其他东西。

let arrayOfEnumsWithoutValues: [Value] = fields.compactMap({
    switch $0.en {
    case let .text(foo), let .two(foo), let .three(foo): if foo == nil { return $0.en } else { return nil }}
})
print("arrayOfEnumsWithoutValues \(arrayOfEnumsWithoutValues)")

// just to check ourselves
if let index = arrayOfEnumsWithoutValues.index(where: { if case .two = $0 { return true }; return false }) {
    print(".two found at index \(index)")
}