스위프트로 작성된 옵서버
옵서버 패턴은 일부 객체들이 다른 객체들에 자신의 상태 변경에 대해 알릴 수 있는 행동 디자인 패턴입니다.
옵서버 패턴은 구독자 인터페이스를 구현하는 모든 객체에 대한 이러한 이벤트들을 구독 및 구독 취소하는 방법을 제공합니다.
복잡도:
인기도:
사용 사례들: 옵서버 패턴은 스위프트 코드, 특히 그래픽 사용자 인터페이스 컴포넌트들에서 매우 일반적입니다. 다른 객체들과의 클래스들과 결합하지 않고 해당 객체들에서 발생하는 이벤트들에 반응하는 방법을 제공합니다.
식별: 옵서버 패턴은 들어오는 메서드들을 목록에 저장하는 구독 메서드로 초기 식별할 수 있으며, 만약 위 구독 메서드가 목록의 객체들을 순회하고 그들의 '업데이트' 메서드를 호출하면 해당 패턴은 옵서버 패턴으로 확정지을 수 있습니다.
개념적인 예시
이 예시는 옵서버 패턴의 구조를 보여주고 다음 질문에 중점을 둡니다:
- 패턴은 어떤 클래스들로 구성되어 있나요?
- 이 클래스들은 어떤 역할을 하나요?
- 패턴의 요소들은 어떻게 서로 연관되어 있나요?
이 패턴의 구조를 배우면 실제 스위프트 사용 사례를 기반으로 하는 다음 예시를 더욱 쉽게 이해할 수 있을 것입니다.
Example.swift: 개념적인 예시
import XCTest
/// The Subject owns some important state and notifies observers when the state
/// changes.
class Subject {
/// For the sake of simplicity, the Subject's state, essential to all
/// subscribers, is stored in this variable.
var state: Int = { return Int(arc4random_uniform(10)) }()
/// @var array List of subscribers. In real life, the list of subscribers
/// can be stored more comprehensively (categorized by event type, etc.).
private lazy var observers = [Observer]()
/// The subscription management methods.
func attach(_ observer: Observer) {
print("Subject: Attached an observer.\n")
observers.append(observer)
}
func detach(_ observer: Observer) {
if let idx = observers.firstIndex(where: { $0 === observer }) {
observers.remove(at: idx)
print("Subject: Detached an observer.\n")
}
}
/// Trigger an update in each subscriber.
func notify() {
print("Subject: Notifying observers...\n")
observers.forEach({ $0.update(subject: self)})
}
/// Usually, the subscription logic is only a fraction of what a Subject can
/// really do. Subjects commonly hold some important business logic, that
/// triggers a notification method whenever something important is about to
/// happen (or after it).
func someBusinessLogic() {
print("\nSubject: I'm doing something important.\n")
state = Int(arc4random_uniform(10))
print("Subject: My state has just changed to: \(state)\n")
notify()
}
}
/// The Observer protocol declares the update method, used by subjects.
protocol Observer: AnyObject {
func update(subject: Subject)
}
/// Concrete Observers react to the updates issued by the Subject they had been
/// attached to.
class ConcreteObserverA: Observer {
func update(subject: Subject) {
if subject.state < 3 {
print("ConcreteObserverA: Reacted to the event.\n")
}
}
}
class ConcreteObserverB: Observer {
func update(subject: Subject) {
if subject.state >= 3 {
print("ConcreteObserverB: Reacted to the event.\n")
}
}
}
/// Let's see how it all works together.
class ObserverConceptual: XCTestCase {
func testObserverConceptual() {
let subject = Subject()
let observer1 = ConcreteObserverA()
let observer2 = ConcreteObserverB()
subject.attach(observer1)
subject.attach(observer2)
subject.someBusinessLogic()
subject.someBusinessLogic()
subject.detach(observer2)
subject.someBusinessLogic()
}
}
Output.txt: 실행 결과
Subject: Attached an observer.
Subject: Attached an observer.
Subject: I'm doing something important.
Subject: My state has just changed to: 4
Subject: Notifying observers...
ConcreteObserverB: Reacted to the event.
Subject: I'm doing something important.
Subject: My state has just changed to: 2
Subject: Notifying observers...
ConcreteObserverA: Reacted to the event.
Subject: Detached an observer.
Subject: I'm doing something important.
Subject: My state has just changed to: 8
Subject: Notifying observers...
실제 사례 예시
Example.swift: 실제 사례 예시
import XCTest
class ObserverRealWorld: XCTestCase {
func test() {
let cartManager = CartManager()
let navigationBar = UINavigationBar()
let cartVC = CartViewController()
cartManager.add(subscriber: navigationBar)
cartManager.add(subscriber: cartVC)
let apple = Food(id: 111, name: "Apple", price: 10, calories: 20)
cartManager.add(product: apple)
let tShirt = Clothes(id: 222, name: "T-shirt", price: 200, size: "L")
cartManager.add(product: tShirt)
cartManager.remove(product: apple)
}
}
protocol CartSubscriber: CustomStringConvertible {
func accept(changed cart: [Product])
}
protocol Product {
var id: Int { get }
var name: String { get }
var price: Double { get }
func isEqual(to product: Product) -> Bool
}
extension Product {
func isEqual(to product: Product) -> Bool {
return id == product.id
}
}
struct Food: Product {
var id: Int
var name: String
var price: Double
/// Food-specific properties
var calories: Int
}
struct Clothes: Product {
var id: Int
var name: String
var price: Double
/// Clothes-specific properties
var size: String
}
class CartManager {
private lazy var cart = [Product]()
private lazy var subscribers = [CartSubscriber]()
func add(subscriber: CartSubscriber) {
print("CartManager: I'am adding a new subscriber: \(subscriber.description)")
subscribers.append(subscriber)
}
func add(product: Product) {
print("\nCartManager: I'am adding a new product: \(product.name)")
cart.append(product)
notifySubscribers()
}
func remove(subscriber filter: (CartSubscriber) -> (Bool)) {
guard let index = subscribers.firstIndex(where: filter) else { return }
subscribers.remove(at: index)
}
func remove(product: Product) {
guard let index = cart.firstIndex(where: { $0.isEqual(to: product) }) else { return }
print("\nCartManager: Product '\(product.name)' is removed from a cart")
cart.remove(at: index)
notifySubscribers()
}
private func notifySubscribers() {
subscribers.forEach({ $0.accept(changed: cart) })
}
}
extension UINavigationBar: CartSubscriber {
func accept(changed cart: [Product]) {
print("UINavigationBar: Updating an appearance of navigation items")
}
open override var description: String { return "UINavigationBar" }
}
class CartViewController: UIViewController, CartSubscriber {
func accept(changed cart: [Product]) {
print("CartViewController: Updating an appearance of a list view with products")
}
open override var description: String { return "CartViewController" }
}
Output.txt: 실행 결과
CartManager: I'am adding a new subscriber: UINavigationBar
CartManager: I'am adding a new subscriber: CartViewController
CartManager: I'am adding a new product: Apple
UINavigationBar: Updating an appearance of navigation items
CartViewController: Updating an appearance of a list view with products
CartManager: I'am adding a new product: T-shirt
UINavigationBar: Updating an appearance of navigation items
CartViewController: Updating an appearance of a list view with products
CartManager: Product 'Apple' is removed from a cart
UINavigationBar: Updating an appearance of navigation items
CartViewController: Updating an appearance of a list view with products
