Swift 协议

协议 属性

import UIKit

// 协议 属性
protocol FullyNamed {
    var fullName: String {
        get
    }
}

struct Person: FullyNamed {
    var fullName: String
}

let john = Person(fullName: "John Appleseed")
print("john.fullName is \(john.fullName)")

class Starship: FullyNamed {
    var prefix: String?
    var name: String
    init(name: String, prefix: String? = nil) {
        self.name = name
        self.prefix = prefix
    }
    
    var fullName: String {
        return (prefix != nil ? prefix! + " " : "") + name
    }
}

var ncc1992 = Starship(name: "Enterprise", prefix: "USS")
print("ncc1992.fullName is \(ncc1992.fullName)")

console log 如下

协议 属性.png

协议 方法

// 协议 方法
protocol RandomNumberGenerator {
    func random() -> Double
}

class LinearCongruentialGenerator: RandomNumberGenerator {
    var lastRandom = 42.0
    let m = 139968.0
    let a = 3877.0
    let c = 29573.0
    func random() -> Double {
        lastRandom = (lastRandom * a + c) % m
        return lastRandom / m
    }
}

let generator = LinearCongruentialGenerator()
print("Here's a random number: \(generator.random())")
print("And another one: \(generator.random())")

protocol Togglable {
    mutating func toogle()
}

enum OnOffSwitch: Togglable {
    case off, on
    mutating func toogle() {
        switch self {
        case .off:
            self = .on
        case .on:
            self = .off
        }
    }
}

var lightSwitch = OnOffSwitch.off
lightSwitch.toogle()

console log 如下

协议 方法.png

协议 初始化函数

// 协议 初始化函数
protocol SomeProtocol {
    init()
}

class SomeClass: SomeProtocol {
    required init()
    {
        
    }
}

class SomeSuperClass {
    init() {
        
    }
}

class SomeSubClass: SomeSuperClass, SomeProtocol {
    required override init() {
        
    }
}

协议 作为类型

// 协议 作为类型
class Dice {
    let sides: Int
    let generator: RandomNumberGenerator
    init(sides: Int, generator: RandomNumberGenerator) {
        self.sides = sides
        self.generator = generator
    }
    
    func roll() -> Int {
        return Int(generator.random() * Double(sides)) + 1
    }
}

var d6 = Dice(sides: 6, generator: LinearCongruentialGenerator())
for _ in 1...5 {
    print("Random dice roll is \(d6.roll())")
}

protocol DiceGame {
    var dice: Dice {
        get
    }
    
    func play()
}

protocol DiceGameDelegate {
    func gameDidStart(game: DiceGame)
    func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll: Int)
    func gameDidEnd(game: DiceGame)
}

class SnakesAndLadders: DiceGame {
    let finalSquare = 25
    let dice = Dice(sides: 6, generator: LinearCongruentialGenerator())
    var square = 0
    var board: [Int]
    init() {
        board = Array(count: finalSquare + 1, repeatedValue: 0)
        board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02
        board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08
    }
    
    var delegate: DiceGameDelegate?
    func play() {
        square = 0
        delegate?.gameDidStart(self)
        gameLoop: while square != finalSquare {
            let diceRoll = dice.roll()
            delegate?.game(self, didStartNewTurnWithDiceRoll: diceRoll)
            
            switch square + diceRoll {
            case finalSquare:
                break gameLoop
            case let newSquare where newSquare > finalSquare:
                continue gameLoop
            default:
                square += diceRoll
                square += board[square]
            }
        }
        
        delegate?.gameDidEnd(self)
    }
}

class DiceGameTracker: DiceGameDelegate {
    var numberOfTurns = 0
    func gameDidStart(game: DiceGame) {
        numberOfTurns = 0
        if game is SnakesAndLadders {
            print("Started a new game of Snakes and Ladders")
        }
        
        print("The game is using a \(game.dice.sides)-sided dice")
    }
    
    func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll: Int) {
        numberOfTurns += 1
        print("Rolled a \(diceRoll)")
    }
    
    func gameDidEnd(game: DiceGame) {
        print("The game lasted for \(numberOfTurns) turns")
    }
}

let tracker = DiceGameTracker()
let game = SnakesAndLadders()
game.delegate = tracker
game.play()

console log 如下

协议 作为类型.png

通过扩展添加协议

// 通过扩展添加协议
protocol TextRepresentable {
    var textualDescription: String {
        get
    }
}

extension Dice: TextRepresentable {
    var textualDescription: String {
        return "A \(sides)-sided dice"
    }
}

print("通过扩展添加协议")
let d12 = Dice(sides: 12, generator: LinearCongruentialGenerator())
print(d12.textualDescription)

extension SnakesAndLadders: TextRepresentable {
    var textualDescription: String {
        return "A game of Snakes and Ladders with \(finalSquare) squares"
    }
}

print(game.textualDescription)

console log 如下

通过扩展添加协议.png

扩展遵守 协议

// 扩展遵守 协议
struct Hamster {
    var name: String
    var textualDescription: String {
        return "A hamster named \(name)"
    }
}

extension Hamster: TextRepresentable {
    
}

let simonTheHamster = Hamster(name: "Simon")
let somethingTextRepresentable: TextRepresentable = simonTheHamster
print("扩展遵守 协议")
print(somethingTextRepresentable.textualDescription)

console log 如下

扩展遵守 协议.png

协议作为集合类型

// 协议作为集合类型
print("协议作为集合类型")
let things: [TextRepresentable] = [game, d12, simonTheHamster]

for thing in things {
    print(thing.textualDescription)
}

console log 如下

协议作为集合类型.png

协议的继承

// 协议的继承
protocol PrettyTextRepresentable: TextRepresentable {
    var prettyTextualDescription: String {
        get
    }
}

extension SnakesAndLadders: PrettyTextRepresentable {
    var prettyTextualDescription: String {
        var output = textualDescription + ":\n"
        for index in 1...finalSquare {
            switch board[index] {
            case let ladder where ladder > 0:
                output += "▲ "
            case let snake where snake < 0:
                output += "▼ "
            default:
                output += "○ "
            }
        }
        return output
    }
}

print("协议的继承")
print(game.prettyTextualDescription)

console log 如下

协议的继承.png

协议的组合

// 协议的组合
protocol Named {
    var name: String {
        get
    }
}

protocol Aged {
    var age: Int {
        get
    }
}

struct AnotherPerson: Named, Aged {
    var name: String
    var age: Int
}

func wishHappyBirthday(celebrator: protocol<Named, Aged>) {
    print("Happy birthday, \(celebrator.name), you're \(celebrator.age)!")
}

print("协议的组合")
let birthdayPerson = AnotherPerson(name: "Yao", age: 24)
wishHappyBirthday(birthdayPerson)

console log 如下

协议的组合.png

判断是否遵守协议

// 判断是否遵守协议
protocol HasArea {
    var area: Double {
        get
    }
}

class Circle: HasArea {
    let pi = 2.1415927
    var radius: Double
    var area: Double {
        return pi * radius * radius
    }
    init(radius: Double) {
        self.radius = radius
    }
}

class Country: HasArea {
    var area: Double
    init(area: Double) {
        self.area = area
    }
}

class Animal {
    var legs: Int
    init(legs: Int) {
        self.legs = legs
    }
}

let objects: [AnyObject] = [
    Circle(radius: 2.0),
    Country(area: 243_610),
    Animal(legs: 4)
]

print("判断是否遵守协议")
for object in objects {
    if let objectWithArea = object as? HasArea {
        print("Area is \(objectWithArea.area)")
    } else {
        print("Something that doesn't have an area")
    }
}

console log 如下

判断是否遵守协议.png

可选协议

// 可选协议
// @objc 声明的协议只能被类遵守，不能被结构体或者枚举遵守
@objc protocol CounterDataSource {
    @objc optional func increment(count: Int) -> Int
    @objc optional var fixedIncrement: Int {
        get
    }
}

class Counter {
    var count = 0
    var dataSource: CounterDataSource?
    func increment() {
        if let amount = dataSource?.increment?(count) {
            count += amount
        } else if let amount = dataSource?.fixedIncrement {
            count += amount
        }
    }
}

class ThreeSource: NSObject, CounterDataSource {
    let fixedIncrement = 3
}

print("可选协议")
var counter = Counter()
counter.dataSource = ThreeSource()
for _ in 1...4 {
    counter.increment()
    print(counter.count)
}

@objc class TowardsZeroSource: NSObject, CounterDataSource {
    func increment(count: Int) -> Int {
        if count == 0 {
            return 0
        } else if count < 0 {
            return 1
        } else {
            return -1
        }
    }
}

var anotherCounter = Counter()
anotherCounter.count = -4
anotherCounter.dataSource = TowardsZeroSource()
for _ in 1...5 {
    anotherCounter.increment()
    print(anotherCounter.count)
}

console log 如下

可选协议.png

协议的扩展

// 协议的扩展
extension RandomNumberGenerator {
    func randomBool() -> Bool {
        return random() > 0.5
    }
}

print("协议的扩展")
let anotherGenerator = LinearCongruentialGenerator()
print("Here's a random number: \(anotherGenerator.random())")
print("And here's a random Boolean: \(anotherGenerator.randomBool())")

console log 如下

协议的扩展.png

扩展协议提供默认实现

// 扩展协议提供默认实现
extension PrettyTextRepresentable {
    var prettyTextualDescription: String {
        return textualDescription
    }
}

扩展协议添加限制

// 扩展协议添加限制
extension CollectionType where Generator.Element: TextRepresentable {
    var textualDescription: String {
        let itemsAsText = self.map{
            $0.textualDescription
        }
        
        return "[" + itemsAsText.joinWithSeparator(",") + "]"
    }
}

let jackTheHamster = Hamster(name: "Jack")
let fiveTwoZeroTheHamster = Hamster(name: "520")
let yaoTheHamster = Hamster(name: "Yao")

let hamsters = [jackTheHamster, fiveTwoZeroTheHamster, yaoTheHamster]

print("扩展协议添加限制")
print(hamsters.textualDescription)

console log 如下

扩展协议添加限制.png