
Factory Method em C#
O Factory method é um padrão de projeto criacional, que resolve o problema de criar objetos de produtos sem especificar suas classes concretas.
O Factory Method define um método, que deve ser usado para criar objetos em vez da chamada direta ao construtor (operador new
). As subclasses podem substituir esse método para alterar a classe de objetos que serão criados.
Se você não conseguir descobrir a diferença entre os padrões Factory, Factory Method e Abstract Factory, leia nossa Comparação Factory.
Complexidade:
Popularidade:
Exemplos de uso: O padrão Factory Method é amplamente utilizado no código C#. É muito útil quando você precisa fornecer um alto nível de flexibilidade para seu código.
Identificação: Os métodos fábrica podem ser reconhecidos por métodos de criação, que criam objetos de classes concretas, mas os retornam como objetos de tipo ou interface abstrata.
Exemplo conceitual
Este exemplo ilustra a estrutura do padrão de projeto Factory Method. 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?
Program.cs: Exemplo conceitual
using System; namespace RefactoringGuru.DesignPatterns.FactoryMethod.Conceptual { // The Creator class declares the factory method that is supposed to return // an object of a Product class. The Creator's subclasses usually provide // the implementation of this method. abstract class Creator { // Note that the Creator may also provide some default implementation of // the factory method. public abstract IProduct FactoryMethod(); // Also note that, despite its name, the Creator's primary // responsibility is not creating products. Usually, it contains some // core business logic that relies on Product objects, returned by the // factory method. Subclasses can indirectly change that business logic // by overriding the factory method and returning a different type of // product from it. public string SomeOperation() { // Call the factory method to create a Product object. var product = FactoryMethod(); // Now, use the product. var result = "Creator: The same creator's code has just worked with " + product.Operation(); return result; } } // Concrete Creators override the factory method in order to change the // resulting product's type. class ConcreteCreator1 : Creator { // Note that the signature of the method still uses the abstract product // type, even though the concrete product is actually returned from the // method. This way the Creator can stay independent of concrete product // classes. public override IProduct FactoryMethod() { return new ConcreteProduct1(); } } class ConcreteCreator2 : Creator { public override IProduct FactoryMethod() { return new ConcreteProduct2(); } } // The Product interface declares the operations that all concrete products // must implement. public interface IProduct { string Operation(); } // Concrete Products provide various implementations of the Product // interface. class ConcreteProduct1 : IProduct { public string Operation() { return "{Result of ConcreteProduct1}"; } } class ConcreteProduct2 : IProduct { public string Operation() { return "{Result of ConcreteProduct2}"; } } class Client { public void Main() { Console.WriteLine("App: Launched with the ConcreteCreator1."); ClientCode(new ConcreteCreator1()); Console.WriteLine(""); Console.WriteLine("App: Launched with the ConcreteCreator2."); ClientCode(new ConcreteCreator2()); } // The client code works with an instance of a concrete creator, albeit // through its base interface. As long as the client keeps working with // the creator via the base interface, you can pass it any creator's // subclass. public void ClientCode(Creator creator) { // ... Console.WriteLine("Client: I'm not aware of the creator's class," + "but it still works.\n" + creator.SomeOperation()); // ... } } class Program { static void Main(string[] args) { new Client().Main(); } } }
Output.txt: Resultados da execução
App: Launched with the ConcreteCreator1. Client: I'm not aware of the creator's class, but it still works. Creator: The same creator's code has just worked with {Result of ConcreteProduct1} App: Launched with the ConcreteCreator2. Client: I'm not aware of the creator's class, but it still works. Creator: The same creator's code has just worked with {Result of ConcreteProduct2}