swift -- 枚举

基本用法

什么时候使用枚举?

结果是固定几种取值的时候

//第一种写法:
enum Seaon {
    case summer
    case winter
    case spring
    case autumn
}

//第二种写法:
enum win {
    case summer,winter, spring, autumn
}

//两种写法是等价的

var fes = Seaon.spring
fes = Seaon.summer
fes = .winter

switch(fes){
case .summer :
    print("夏天")
case .winter :
    print("冬天")
case .spring :
    print("春天")
default:
    print("秋天")
}

关联值(Associated Values)

• 有时将枚举的成员值跟其他类型的值关联存储在一起 (将各种类型的值存储到枚举变量中) ,会非常有用

enum Score {
    case points(Int) //定义时候定义类型就行,可以不写标签名
    case grade (Character)
}

var score = Score.points(96)
score = .grade("A")

switch score {
case let .points(i):
    print(i,"points")
case let .grade(i):
    print("grade",i)
}
//grade A


enum Date {
    case digit(year: Int, month: Int, day: Int)//标签名更容易读懂
    case string (String)
}

var date = Date.digit(year:2011 ,month:9,day:10)
date = .string("2011-09-10" )
switch date {
case .digit(let year,let month,let day)://这样写也可以 case .digit(year: let year,month: let month,day: let day):
    print(year, month, day)
case let .string(value):
    print (value)
}

// 必要时let也可以改为var

关联值举例

enum Password {
    case number(Int, Int, Int, Int)
    case gesture(String)
}

var pwd = Password.number(3, 5, 7 ,8)
pwd = .gesture("12369")

pwd = .gesture("12369")
switch pwd {
case let .number(n1, n2, n3, n4):
    print("number is ", n1, n2, n3, n4)
case let .gesture(str):
    print("gesture is",str)
}

原始值(Raw Values)

• 枚举成员可以使用相同类型的默认值预先对应，这个默认值叫做:原始值

enum PokerSuit : Character {
    case spade = "♠"
    case heart = "♥"
    case diamond = "♦"
    case club = "♣"
}

var suit = PokerSuit.spade
print(suit) // spade
print(suit.rawValue) // ♠
print(PokerSuit.club.rawValue) // ♣

enum Grade : String {
    case perfect = "A"
    case great = "B"
    case good = "C"
    case bad = "D"
}

print(Grade.perfect.rawValue) // A
print(Grade.great.rawValue) // B
print(Grade.good.rawValue) // C
print(Grade.bad.rawValue) // D

• 注意:原始值不占用枚举变量的内存

隐式原始值(Implicitly Assigned Raw Values)

• 如果枚举的原始值类型是Int、String，Swift会自动分配原始值

enum Direction : String {
    case north = "north"
    case south = "south"
    case east = "east"
    case west = "west"
}

// 等价于

enum Direction : String {
    case north, south, east, west
}

print(Direction.north.rawValue) // north
print(Direction.north) // north

enum Season : Int {
    case spring, summer, autumn, winter
}
print(Season.spring.rawValue) // 0
print(Season.summer.rawValue) // 1
print(Season.autumn.rawValue) // 2
print(Season.winter.rawValue) // 3

enum Season : Int {
    case spring = 1, summer, autumn = 4, winter
}

print(Season.spring.rawValue) // 1
print(Season.summer.rawValue) // 2
print(Season.autumn.rawValue) // 4
print(Season.winter.rawValue) // 5