无论枚举大小写如何，如何快速获取枚举的关联值

Question

我有一个对象 FormField，它有两个属性：一个字符串name，和一个可以接受任何类型的value——因此我把它做成了Any!。但是，a separate question 告诉我使用带有关联值的枚举而不是 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性变得非常冗长。如果我想为表单中的所有缺失字段显示警报视图，我将不得不在 switch 语句中对每个案例重复一次 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)
            }
        }
    }
}

是否有更短的方法来访问枚举的关联值，而不管其类型如何？如果我将 FormField.value 设为 Any!，则上面的代码将很简单：

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

Answer 1

在enum 中定义一个方法isMissing() - 只写一次。然后，您几乎可以得到您喜欢的东西：

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

看起来像这样（来自 Swift 解释器）：

  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

在 Swift 2 中，可以使用反射获取关联的值。

为了更简单，只需将以下代码添加到您的项目中，并使用 EVAssociated 协议扩展您的枚举。

    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 它还有一个很好的枚举扩展，用于枚举所有枚举值。

Answer 3

如果所有枚举案例的关联值都属于同一类型，则以下方法可能会有所帮助。

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)")

许多其他的东西也可以类似地获得。

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)")
}