Swift协议（Protocol）

协议是为方法、属性等定义一套规范。没有详细的实现。

协议可以被类、结构体等详细实现（或遵守）。

protocol SomeProtocol {
// protocoldefinition goes here
}
struct         SomeStructure:            FirstProtocol, AnotherProtocol {
// structure definition goes here}
class  SomeClass:    SomeSuperclass,     FirstProtocol, AnotherProtocol {
// class definitiongoeshere
}

属性

1. set 和 get 訪问器

protocol SomeProtocol {
var mustBeSettable:Int { get set }
var doesNotNeedToBeSettable: Int { get }
}

2.静态属性

protocol AnotherProtocol {
class var someTypeProperty: Int { get set }
}

3.仅仅读

protocol FullyNamed {
var fullName: String { get }
}

实例：

struct Person: FullyNamed {
varfullName: String
}
letjohn= Person(fullName: "John Appleseed")
class Starship: FullyNamed {
varprefix: String?
varname: String
init(name: String, prefix: String? = nil) {
self.name = name self.prefix = prefix
}
varfullName: String {
return (prefix ? prefix!+ " " :"")+ name
}
}
varncc1701 = Starship(name: "Enterprise",prefix: "USS")

方法

1.定义方法

protocol RandomNumberGenerator{
func random() -> Double
}

2.定义静态方法

protocolSomeProtocol {
class func someTypeMethod()
}

实例：

protocol RandomNumberGenerator{
funcrandom() -> Double
}
class                   LinearCongruentialGenerator:RandomNumberGenerator {
var lastRandom= 42.0let m = 139968.0
let a = 3877.0 let c = 29573.0
funcrandom() -> Double {
lastRandom = ((lastRandom * a + c) %m)
returnlastRandom / m
}
}
let generator= LinearCongruentialGenerator()
println("Here's       a        random         number:
\(generator.random())")
//    prints    "Here's     a     random       number:0.37464991998171"
println("And another one: \(generator.random())")
//prints "And another one: 0.729023776863283"

把协议作为类型使用

protocol RandomNumberGenerator {
func random() -> Double}
class LinearCongruentialGenerator: RandomNumberGenerator {
varlastRandom= 42.0 let m =139968.0
let a = 3877.0 letc = 29573.0
func random() -> Double {
lastRandom = ((lastRandom * a + c) %m)
return lastRandom / m
}
}
class Dice {
letsides: Int
let generator: RandomNumberGenerator
init(sides: Int, generator: RandomNumberGenerator) {
self.sides = sidesself.generator = generator
}
func roll() -> Int{
return Int(generator.random() * Double(sides)) + 1
}
}
vard6 = Dice(sides: 6, generator: LinearCongruentialGenerator())
for_ in 1...5 {
println("Randomdiceroll is \(d6.roll())")
}

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