C# 工厂方法模式讲解和代码示例
工厂方法是一种创建型设计模式， 解决了在不指定具体类的情况下创建产品对象的问题。
工厂方法定义了一个方法， 且必须使用该方法代替通过直接调用构造函数来创建对象 （ new操作符） 的方式。 子类可重写该方法来更改将被创建的对象所属类。
如果你不清楚工厂、 工厂方法和抽象工厂模式之间的区别， 请参阅工厂模式比较。
复杂度：
流行度：
使用示例： 工厂方法模式在 C# 代码中得到了广泛使用。 当你需要在代码中提供高层次的灵活性时， 该模式会非常实用。
识别方法： 工厂方法可通过构建方法来识别， 它会创建具体类的对象， 但以抽象类型或接口的形式返回这些对象。
概念示例
本例说明了工厂方法设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
Program.cs: 概念示例
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: 执行结果
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} 
