Mediator w języku Swift
Mediator to behawioralny wzorzec projektowy pozwalający zredukować sprzężenie pomiędzy komponentami programu poprzez zmuszenie ich do komunikacji za pośrednictwem obiektu zwanego mediatorem.
Mediator ułatwia modyfikację, rozszerzanie i ponowne wykorzystanie komponentów gdyż z jego pomocą nie są one zależne od wielu innych klas.
Złożoność:
Popularność:
Przykłady użycia: Najpopularniejsze zastosowanie wzorca Mediator w kodzie Swift to umożliwienie komunikacji pomiędzy komponentami graficznego interfejsu użytkownika. Synonimem nazwy Mediator jest Kontroler — znany z wzorca MVC (ang. Model View Controller — Model Widok Kontroler).
Następujące przykłady są dostępne na Swift Playgrounds.
Gratulacje dla Alejandro Mohamad za stworzenie wersji Playground.
Przykład koncepcyjny
Poniższy przykład ilustruje strukturę wzorca Mediator ze szczególnym naciskiem na następujące kwestie:
- Z jakich składa się klas?
- Jakie role pełnią te klasy?
- W jaki sposób elementy wzorca są ze sobą powiązane?
Poznawszy strukturę wzorca będzie ci łatwiej zrozumieć następujący przykład, oparty na prawdziwym przypadku użycia Swift.
Example.swift: Przykład koncepcyjny
import XCTest /// The Mediator interface declares a method used by components to notify the /// mediator about various events. The Mediator may react to these events and /// pass the execution to other components. protocol Mediator: AnyObject { func notify(sender: BaseComponent, event: String) } /// Concrete Mediators implement cooperative behavior by coordinating several /// components. 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() } } } /// The Base Component provides the basic functionality of storing a mediator's /// instance inside component objects. class BaseComponent { fileprivate weak var mediator: Mediator? init(mediator: Mediator? = nil) { self.mediator = mediator } func update(mediator: Mediator) { self.mediator = mediator } } /// Concrete Components implement various functionality. They don't depend on /// other components. They also don't depend on any concrete mediator classes. 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") } } /// Let's see how it all works together. 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: Wynik działania
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. Przykład z prawdziwego życia
Example.swift: Przykład z prawdziwego życia
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: Wynik działania
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 
