L’Adaptateur est un patron de conception structurel qui permet à des objets incompatibles de collaborer.
L’adaptateur fait office d’emballeur entre les deux objets. Il récupère les appels à un objet et les met dans un format et une interface reconnaissables par le second objet.
Exemples d’utilisation : L’adaptateur est très répandu en Swift. On le retrouve souvent dans des systèmes basés sur du code hérité, dans lesquels l’adaptateur fait fonctionner du code hérité avec des classes modernes.
Identification : L’adaptateur peut être identifié grâce à son constructeur qui prend une instance d’un type abstrait différent ou d’une interface différente. Lorsque l’une des méthodes de l’adaptateur est appelée, il traduit les paramètres dans un format approprié et redirige l’appel vers une ou plusieurs méthodes de l’objet emballé.
Les exemples suivants sont disponibles sur le site de
Swift Playgrounds.
Félicitations à
Alejandro Mohamad pour avoir créé la version du Playground.
Exemple conceptuel
Dans cet exemple, nous allons voir la structure de l’Adaptateur et répondre aux questions suivantes :
Que contiennent les classes ?
Quels rôles jouent-elles ?
Comment les éléments du patron sont-ils reliés ?
Après avoir étudié la structure du patron, vous pourrez plus facilement comprendre l’exemple suivant qui est basé sur un cas d’utilisation réel en Swift.
Example.swift: Exemple conceptuel
import XCTest
/// The Target defines the domain-specific interface used by the client code.
class Target {
func request() -> String {
return "Target: The default target's behavior."
}
}
/// The Adaptee contains some useful behavior, but its interface is incompatible
/// with the existing client code. The Adaptee needs some adaptation before the
/// client code can use it.
class Adaptee {
public func specificRequest() -> String {
return ".eetpadA eht fo roivaheb laicepS"
}
}
/// The Adapter makes the Adaptee's interface compatible with the Target's
/// interface.
class Adapter: Target {
private var adaptee: Adaptee
init(_ adaptee: Adaptee) {
self.adaptee = adaptee
}
override func request() -> String {
return "Adapter: (TRANSLATED) " + adaptee.specificRequest().reversed()
}
}
/// The client code supports all classes that follow the Target interface.
class Client {
// ...
static func someClientCode(target: Target) {
print(target.request())
}
// ...
}
/// Let's see how it all works together.
class AdapterConceptual: XCTestCase {
func testAdapterConceptual() {
print("Client: I can work just fine with the Target objects:")
Client.someClientCode(target: Target())
let adaptee = Adaptee()
print("Client: The Adaptee class has a weird interface. See, I don't understand it:")
print("Adaptee: " + adaptee.specificRequest())
print("Client: But I can work with it via the Adapter:")
Client.someClientCode(target: Adapter(adaptee))
}
}
Output.txt: Résultat de l’exécution
Client: I can work just fine with the Target objects:
Target: The default target's behavior.
Client: The Adaptee class has a weird interface. See, I don't understand it:
Adaptee: .eetpadA eht fo roivaheb laicepS
Client: But I can work with it via the Adapter:
Adapter: (TRANSLATED) Special behavior of the Adaptee.
Analogie du monde réel
Example.swift: Analogie du monde réel
import XCTest
import UIKit
/// Adapter Design Pattern
///
/// Intent: Convert the interface of a class into the interface clients expect.
/// Adapter lets classes work together that couldn't work otherwise because of
/// incompatible interfaces.
class AdapterRealWorld: XCTestCase {
/// Example. Let's assume that our app perfectly works with Facebook
/// authorization. However, users ask you to add sign in via Twitter.
///
/// Unfortunately, Twitter SDK has a different authorization method.
///
/// Firstly, you have to create the new protocol 'AuthService' and insert
/// the authorization method of Facebook SDK.
///
/// Secondly, write an extension for Twitter SDK and implement methods of
/// AuthService protocol, just a simple redirect.
///
/// Thirdly, write an extension for Facebook SDK. You should not write any
/// code at this point as methods already implemented by Facebook SDK.
///
/// It just tells a compiler that both SDKs have the same interface.
func testAdapterRealWorld() {
print("Starting an authorization via Facebook")
startAuthorization(with: FacebookAuthSDK())
print("Starting an authorization via Twitter.")
startAuthorization(with: TwitterAuthSDK())
}
func startAuthorization(with service: AuthService) {
/// The current top view controller of the app
let topViewController = UIViewController()
service.presentAuthFlow(from: topViewController)
}
}
protocol AuthService {
func presentAuthFlow(from viewController: UIViewController)
}
class FacebookAuthSDK {
func presentAuthFlow(from viewController: UIViewController) {
/// Call SDK methods and pass a view controller
print("Facebook WebView has been shown.")
}
}
class TwitterAuthSDK {
func startAuthorization(with viewController: UIViewController) {
/// Call SDK methods and pass a view controller
print("Twitter WebView has been shown. Users will be happy :)")
}
}
extension TwitterAuthSDK: AuthService {
/// This is an adapter
///
/// Yeah, we are able to not create another class and just extend an
/// existing one
func presentAuthFlow(from viewController: UIViewController) {
print("The Adapter is called! Redirecting to the original method...")
self.startAuthorization(with: viewController)
}
}
extension FacebookAuthSDK: AuthService {
/// This extension just tells a compiler that both SDKs have the same
/// interface.
}
Output.txt: Résultat de l’exécution
Starting an authorization via Facebook
Facebook WebView has been shown
///
Starting an authorization via Twitter
The Adapter is called! Redirecting to the original method...
Twitter WebView has been shown. Users will be happy :)
