O Adapter é um padrão de projeto estrutural, que permite a colaboração de objetos incompatíveis.
O Adapter atua como um wrapper entre dois objetos. Ele captura chamadas para um objeto e as deixa reconhecíveis tanto em formato como interface para este segundo objeto.
Exemplos de uso: O padrão Adapter é bastante comum no código Swift. É frequentemente usado em sistemas baseados em algum código legado. Nesses casos, os adaptadores criam código legado com classes modernas.
Identificação: O adapter é reconhecível por um construtor que utiliza uma instância de tipo abstrato/interface diferente. Quando o adaptador recebe uma chamada para qualquer um de seus métodos, ele converte parâmetros para o formato apropriado e direciona a chamada para um ou vários métodos do objeto envolvido.
Este exemplo ilustra a estrutura do padrão de projeto Adapter. Ele se concentra em responder a estas perguntas:
De quais classes ele consiste?
Quais papéis essas classes desempenham?
De que maneira os elementos do padrão estão relacionados?
Depois de aprender sobre a estrutura do padrão, será mais fácil entender o exemplo a seguir, com base em um caso de uso Swift do mundo real.
Example.swift: Exemplo conceitual
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: Resultados da execução
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.
Exemplo do mundo real
Example.swift: Exemplo do mundo real
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: Resultados da execução
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 :)
