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)
}

DiceGame協(xié)議可以在任意含有骰子的游戲中實(shí)現(xiàn)，DiceGameDelegate協(xié)議可以用來追蹤DiceGame的游戲過程。

如下所示，SnakesAndLadders是Snakes and Ladders(譯者注：控制流章節(jié)有該游戲的詳細(xì)介紹)游戲的新版本。新版本使用Dice作為骰子，并且實(shí)現(xiàn)了DiceGame和DiceGameDelegate協(xié)議

class SnakesAndLadders: DiceGame {
    let finalSquare = 25
    let dic = Dice(sides: 6, generator: LinearCongruentialGenerator())
    var square = 0
    var board: Int[]
    init() {
        board = Int[](count: finalSquare + 1, repeatedValue: 0)
        board[03] = +08; board[06] = +11; borad[09] = +09; board[10] = +02
        borad[14] = -10; board[19] = -11; borad[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)
     }
}

游戲的初始化設(shè)置(setup)被SnakesAndLadders類的構(gòu)造器(initializer)實(shí)現(xiàn)。所有的游戲邏輯被轉(zhuǎn)移到了play方法中。

注意：因?yàn)?code style="box-sizing: border-box; -webkit-tap-highlight-color: transparent; -webkit-font-smoothing: antialiased; font-family: Monaco, Menlo, Consolas, 'Courier New', monospace; font-size: 14px; padding: 0px 5px; color: rgb(199, 37, 78); background-color: rgb(248, 248, 248); white-space: nowrap; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; margin: 0px 2px; border: 1px solid rgb(234, 234, 234);">delegate并不是該游戲的必備條件，delegate被定義為遵循DiceGameDelegate協(xié)議的可選屬性。

DicegameDelegate協(xié)議提供了三個(gè)方法用來追蹤游戲過程。被放置于游戲的邏輯中，即play()方法內(nèi)。分別在游戲開始時(shí)，新一輪開始時(shí)，游戲結(jié)束時(shí)被調(diào)用。

因?yàn)?code style="box-sizing: border-box; -webkit-tap-highlight-color: transparent; -webkit-font-smoothing: antialiased; font-family: Monaco, Menlo, Consolas, 'Courier New', monospace; font-size: 14px; padding: 0px 5px; color: rgb(199, 37, 78); background-color: rgb(248, 248, 248); white-space: nowrap; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; margin: 0px 2px; border: 1px solid rgb(234, 234, 234);">delegate是一個(gè)遵循DiceGameDelegate的可選屬性，因此在play()方法中使用了可選鏈來調(diào)用委托方法。若delegate屬性為nil，則委托調(diào)用優(yōu)雅地失效。若delegate不為nil，則委托方法被調(diào)用

如下所示，DiceGameTracker遵循了DiceGameDelegate協(xié)議

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

DiceGameTracker實(shí)現(xiàn)了DiceGameDelegate協(xié)議的方法要求，用來記錄游戲已經(jīng)進(jìn)行的輪數(shù)。當(dāng)游戲開始時(shí)，numberOfTurns屬性被賦值為0；在每新一輪中遞加；游戲結(jié)束后，輸出打印游戲的總輪數(shù)。

gameDidStart方法從game參數(shù)獲取游戲信息并輸出。game在方法中被當(dāng)做DiceGame類型而不是SnakeAndLadders類型，所以方法中只能訪問DiceGame協(xié)議中的成員。

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Swift委托(代理)模式

委托(代理)模式