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
