工厂模式

定义一个用户创建对象的接口，让子类决定实例化哪一个

1.产品

interface IProduct {
   string ShipFrom();
 }
 
 class ProductA : IProduct {
   public String ShipFrom () {
     return " from South Africa";
   }
 }
 
 class ProductB : IProduct {
   public String ShipFrom () {
           return "from Spain";
   }
 }

2.工厂

每个产品都有一个工厂

interface IProductFactory
 {
     IProduct FactoryMethod();
 }
 
 class ProductFactoryA :IProductFactory
 {
     public IProduct FactoryMethod()
     {
         return new ProductA();
     }
 }
 
 class ProductFactoryB : IProductFactory
 {
     public IProduct FactoryMethod()
     {
         return new ProductB();
     }
 }

3.客户端调用

IProductFactory factory = new ProductFactoryA();
 IProduct Product;
 Product = factory.FactoryMethod();
 factory = new ProductFactoryB();
 Product = factory.FactoryMethod();

与工厂模式比较,这里每个产品都有工厂，虽有扩展性，但每个产品都有工厂也造成了麻烦