【譯】Swift World：設計模式--中介者模式

原文：medium.com/swiftworld/…

作者：Peng

今天我們討論一下中介者模式(Mediator)。這次不從抽象定義開始，而是用現實世界中的一個場景來解釋它。在一個團隊裏，有產品經理，開發工程師，質量工程師。當開發完成了某些功能，將代碼提交到倉庫。相關環節人員，像質量工程師和產品經理需要被通知。

protocol Collogue {
    var id: String { get }
    func send(message: String)
    func receive(message: String)
}
class Developer: Collogue {
    var id: String
    var qe: QE
    var pm: PM
    init(qe: QE, pm: PM) {
        self.id = "Developer"
        self.qe = qe
        self.pm = pm
    }
    func send(message: String) {
        qe.receive(message: message)
        pm.receive(message: message)
    }
    func receive(message: String) {
        print(message)
    }   
}
class QE: Collogue {
    var id: String
    var developer: Developer
    var pm: PM
    init(developer: Developer, pm: PM) {
        self.id = "QE"
        self.developer = developer
        self.pm = pm
    }
    func send(message: String) {
        developer.receive(message: message)
        pm.receive(message: message)
    }
    func receive(message: String) {
        print(message)
    }
}
class PM: Collogue {
    var id: String
    var developer: Developer
    var qe: QE
    init(developer: Developer, qe: QE) {
        self.id = "PM"
        self.developer = developer
        self.qe = qe
    }
    func send(message: String) {
        developer.receive(message: message)
        qe.receive(message: message)
    }
    func receive(message: String) {
        print(message)
    }
}
複製代碼

每個角色都需要持有另一個角色的實例，這種連接方式是高耦合的，且很不容易修改。

現在我們需要一箇中介者幫助我們簡化這個系統。中介者的目的是幫助對象之間相互交流。它讓每個對象都是跟自己進行交互而不是其他對象。當前對象不需要持有別的對象，而是持有中介者。這樣將解耦系統，它的結構圖如下所示：

我們來寫一下代碼：

protocol Mediator {
    func send(message: String, sender: Colleague)
}
class TeamMediator: Mediator {
    var colleagues: [Colleague] = []
    func register(colleague: Colleague) {
        colleagues.append(colleague)
    }
    func send(message: String, sender: Colleague) {
        for colleague in colleagues {
            if colleague.id != sender.id {
                colleague.receive(message: message)
            }
        }
    }
}
複製代碼

通過持有中介者，那幾個角色對象變成了這樣：

protocol Colleague {
    var id: String { get }
    var mediator: Mediator { get }
    func send(message: String)
    func receive(message: String)
}
class Developer: Colleague {
    var id: String
    var mediator: Mediator
    init(mediator: Mediator) {
        self.id = "Developer"
        self.mediator = mediator
    }
    func send(message: String) {
        mediator.send(message: message, sender: self)
    }
    func receive(message: String) {
        print("Developer received: " + message)
    }
}
class QE: Colleague {
    var id: String
    var mediator: Mediator
    init(mediator: Mediator) {
        self.id = "QE"
        self.mediator = mediator
    }
    func send(message: String) {
        mediator.send(message: message, sender: self)
    }
    func receive(message: String) {
        print("QE received: " + message)
    }
}
class PM: Colleague {
    var id: String
    var mediator: Mediator
    init(mediator: Mediator) {
        self.id = "PM"
        self.mediator = mediator
    }
    func send(message: String) {
        mediator.send(message: message, sender: self)
    }
    func receive(message: String) {
        print("PM received: " + message)
    }
}
複製代碼

這樣一來，整個結構就變成了下面這樣：

讓我們用新的方式來使用它：

//usage
let mediator = TeamMediator()
let qe = QE(mediator: mediator)
let developer = Developer(mediator: mediator)
let pm = PM(mediator: mediator)
mediator.register(colleague: developer)
mediator.register(colleague: qe)
mediator.register(colleague: pm)
mediator.send(message: "Hello world!", sender: developer)
複製代碼

另一個相似的例子就是非常受歡迎的Notification(NSNotification)。你可以在網上找到很多相關的代碼。