Посредник на Swift

Посредник — это поведенческий паттерн, который упрощает коммуникацию между компонентами системы.

Посредник убирает прямые связи между отдельными компонентами, заставляя их общаться друг с другом через себя.

Сложность:

Популярность:

Применимость: Пожалуй, самое популярное применение Посредника в Swift-коде — это связь нескольких компонентов GUI одной программы.

Следующие примеры доступны на Swift Playgrounds.

Благодарность Alejandro Mohamad за создание версии Playground.

Концептуальный пример

Этот пример показывает структуру паттерна Посредник, а именно — из каких классов он состоит, какие роли эти классы выполняют и как они взаимодействуют друг с другом.

После ознакомления со структурой, вам будет легче воспринимать второй пример, который рассматривает реальный случай использования паттерна в мире Swift.

Example.swift: Пример структуры паттерна

import XCTest

/// Интерфейс Посредника предоставляет метод, используемый компонентами для
/// уведомления посредника о различных событиях. Посредник может реагировать на
/// эти события и передавать исполнение другим компонентам.
protocol Mediator: AnyObject {

    func notify(sender: BaseComponent, event: String)
}

/// Конкретные Посредники реализуют совместное поведение, координируя отдельные
/// компоненты.
class ConcreteMediator: Mediator {

    private var component1: Component1
    private var component2: Component2

    init(_ component1: Component1, _ component2: Component2) {
        self.component1 = component1
        self.component2 = component2

        component1.update(mediator: self)
        component2.update(mediator: self)
    }

    func notify(sender: BaseComponent, event: String) {
        if event == "A" {
            print("Mediator reacts on A and triggers following operations:")
            self.component2.doC()
        }
        else if (event == "D") {
            print("Mediator reacts on D and triggers following operations:")
            self.component1.doB()
            self.component2.doC()
        }
    }
}

/// Базовый Компонент обеспечивает базовую функциональность хранения экземпляра
/// посредника внутри объектов компонентов.
class BaseComponent {

    fileprivate weak var mediator: Mediator?

    init(mediator: Mediator? = nil) {
        self.mediator = mediator
    }

    func update(mediator: Mediator) {
        self.mediator = mediator
    }
}

/// Конкретные Компоненты реализуют различную функциональность. Они не зависят
/// от других компонентов. Они также не зависят от каких-либо конкретных классов
/// посредников.
class Component1: BaseComponent {

    func doA() {
        print("Component 1 does A.")
        mediator?.notify(sender: self, event: "A")
    }

    func doB() {
        print("Component 1 does B.\n")
        mediator?.notify(sender: self, event: "B")
    }
}

class Component2: BaseComponent {

    func doC() {
        print("Component 2 does C.")
        mediator?.notify(sender: self, event: "C")
    }

    func doD() {
        print("Component 2 does D.")
        mediator?.notify(sender: self, event: "D")
    }
}

/// Давайте посмотрим как всё это будет работать.
class MediatorConceptual: XCTestCase {

    func testMediatorConceptual() {

        let component1 = Component1()
        let component2 = Component2()

        let mediator = ConcreteMediator(component1, component2)
        print("Client triggers operation A.")
        component1.doA()

        print("\nClient triggers operation D.")
        component2.doD()

        print(mediator)
    }
}

Output.txt: Результат выполнения

Client triggers operation A.
Component 1 does A.
Mediator reacts on A and triggers following operations:
Component 2 does C.

Client triggers operation D.
Component 2 does D.
Mediator reacts on D and triggers following operations:
Component 1 does B.

Component 2 does C.

Пример из реальной жизни

Example.swift: Пример из реальной жизни

import XCTest

class MediatorRealWorld: XCTestCase {

    func test() {

        let newsArray = [News(id: 1, title: "News1", likesCount: 1),
                         News(id: 2, title: "News2", likesCount: 2)]

        let numberOfGivenLikes = newsArray.reduce(0, { $0 + $1.likesCount })

        let mediator = ScreenMediator()

        let feedVC = NewsFeedViewController(mediator, newsArray)
        let newsDetailVC = NewsDetailViewController(mediator, newsArray.first!)
        let profileVC = ProfileViewController(mediator, numberOfGivenLikes)

        mediator.update([feedVC, newsDetailVC, profileVC])

        feedVC.userLikedAllNews()
        feedVC.userDislikedAllNews()
    }
}

class NewsFeedViewController: ScreenUpdatable {

    private var newsArray: [News]
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ newsArray: [News]) {
        self.newsArray = newsArray
        self.mediator = mediator
    }

    func likeAdded(to news: News) {

        print("News Feed: Received a liked news model with id \(news.id)")

        for var item in newsArray {
            if item == news {
                item.likesCount += 1
            }
        }
    }

    func likeRemoved(from news: News) {

        print("News Feed: Received a disliked news model with id \(news.id)")

        for var item in newsArray {
            if item == news {
                item.likesCount -= 1
            }
        }
    }

    func userLikedAllNews() {
        print("\n\nNews Feed: User LIKED all news models")
        print("News Feed: I am telling to mediator about it...\n")
        newsArray.forEach({ mediator?.likeAdded(to: $0) })
    }

    func userDislikedAllNews() {
        print("\n\nNews Feed: User DISLIKED all news models")
        print("News Feed: I am telling to mediator about it...\n")
        newsArray.forEach({ mediator?.likeRemoved(from: $0) })
    }
}

class NewsDetailViewController: ScreenUpdatable {

    private var news: News
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ news: News) {
        self.news = news
        self.mediator = mediator
    }

    func likeAdded(to news: News) {
        print("News Detail: Received a liked news model with id \(news.id)")
        if self.news == news {
            self.news.likesCount += 1
        }
    }

    func likeRemoved(from news: News) {
        print("News Detail: Received a disliked news model with id \(news.id)")
        if self.news == news {
            self.news.likesCount -= 1
        }
    }
}

class ProfileViewController: ScreenUpdatable {

    private var numberOfGivenLikes: Int
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ numberOfGivenLikes: Int) {
        self.numberOfGivenLikes = numberOfGivenLikes
        self.mediator = mediator
    }

    func likeAdded(to news: News) {
        print("Profile: Received a liked news model with id \(news.id)")
        numberOfGivenLikes += 1
    }

    func likeRemoved(from news: News) {
        print("Profile: Received a disliked news model with id \(news.id)")
        numberOfGivenLikes -= 1
    }
}

protocol ScreenUpdatable: class {

    func likeAdded(to news: News)

    func likeRemoved(from news: News)
}

class ScreenMediator: ScreenUpdatable {

    private var screens: [ScreenUpdatable]?

    func update(_ screens: [ScreenUpdatable]) {
        self.screens = screens
    }

    func likeAdded(to news: News) {
        print("Screen Mediator: Received a liked news model with id \(news.id)")
        screens?.forEach({ $0.likeAdded(to: news) })
    }

    func likeRemoved(from news: News) {
        print("ScreenMediator: Received a disliked news model with id \(news.id)")
        screens?.forEach({ $0.likeRemoved(from: news) })
    }
}

struct News: Equatable {

    let id: Int

    let title: String

    var likesCount: Int

    /// Other properties

    static func == (left: News, right: News) -> Bool {
        return left.id == right.id
    }
}

Output.txt: Результат выполнения

News Feed: User LIKED all news models
News Feed: I am telling to mediator about it...

Screen Mediator: Received a liked news model with id 1
News Feed: Received a liked news model with id 1
News Detail: Received a liked news model with id 1
Profile: Received a liked news model with id 1
Screen Mediator: Received a liked news model with id 2
News Feed: Received a liked news model with id 2
News Detail: Received a liked news model with id 2
Profile: Received a liked news model with id 2


News Feed: User DISLIKED all news models
News Feed: I am telling to mediator about it...

ScreenMediator: Received a disliked news model with id 1
News Feed: Received a disliked news model with id 1
News Detail: Received a disliked news model with id 1
Profile: Received a disliked news model with id 1
ScreenMediator: Received a disliked news model with id 2
News Feed: Received a disliked news model with id 2
News Detail: Received a disliked news model with id 2
Profile: Received a disliked news model with id 2

Посредник на Swift

Концептуальный пример

Example.swift: Пример структуры паттерна

Output.txt: Результат выполнения

Пример из реальной жизни

Example.swift: Пример из реальной жизни

Output.txt: Результат выполнения

Посредник на других языках программирования