DDWiki/实践/后端/项目/12.工厂模式.md

简单工厂

• 简单/简易工厂并不是一个设计模式, 更多是一个编程习惯. 但是使用的非常广泛.
• 例如披萨店的实例

用C#/.net core实现简单工厂

• Pizza的父类 ``` using System; using System.Collections.Generic;

namespace SimpleFactory.Pizzas {

public abstract class Pizza
{
    public string Name { get; protected set; }
    public string Dough { get; protected set; }
    public string Sauce { get; protected set; }
    protected List<string> Toppings = new List<string>();

    public void Prepare()
    {
        Console.WriteLine($"Preparing: {Name}");
        Console.WriteLine($"Tossing: {Dough}");
        Console.WriteLine($"Adding sauce: {Sauce}");
        Console.WriteLine("Adding toppings: ");
        Toppings.ForEach(x => Console.WriteLine($"  {x}"));
    }

    public void Bake()
    {
        Console.WriteLine("Bake for 25 minutes");
    }

    public void Cut()
    {
        Console.WriteLine("Cutting the pizza into diagnol slices");
    }

    public void Box()
    {
        Console.WriteLine("Placing pizza in official PizzaStore box......");
    }
}

}

- 各种Pizza

namespace SimpleFactory.Pizzas {

public class CheesePizza: Pizza
{
    public CheesePizza()
    {
        Name = "Cheese Pizza";
        Dough = "Think Dough";
        Sauce = "Salad";
        Toppings.Add("Grated Reggiano Cheese");
    }
}

}

namespace SimpleFactory.Pizzas {

public class ClamPizza: Pizza
{
    public ClamPizza()
    {
        Name = "Clam Pizza";
        Sauce = "Tomato sauce";
        Dough = "Soft dough";
        Toppings.Add("Shrimp meat");
    }
}

}

namespace SimpleFactory.Pizzas {

public class PepperoniPizza: Pizza
{
    public PepperoniPizza()
    {
        Name = "Pepperoni Pizza";
        Dough = "Thin dough";
        Sauce = "Black pepper";
        Toppings.Add("Beef Granules");
        Toppings.Add("Niblet");
    }
}

}

- 简单工厂

using SimpleFactory.Pizzas;

namespace SimpleFactory {

public class SimplePizzaFactory
{
    public Pizza CreatePizza(string type)
    {
        Pizza pizza = null;
        switch (type)
        {
            case "cheese":
                pizza = new CheesePizza();
                break;
            case "pepperoni":
                pizza = new PepperoniPizza();
                break;
            case "clam":
                pizza = new ClamPizza();
                break;
        }

        return pizza;
    }
}

}

- PizzaStore

using SimpleFactory.Pizzas;

namespace SimpleFactory {

public class PizzaStore
{
    private readonly SimplePizzaFactory _factory;

    public PizzaStore(SimplePizzaFactory factory)
    {
        _factory = factory;
    }

    public Pizza OrderPizza(string type)
    {
        var pizza = _factory.CreatePizza(type);
        pizza.Prepare();
        pizza.Bake();
        pizza.Cut();
        pizza.Box();
        return pizza;
    }
}

} ```

工厂方法模式

• 工厂方法模式定义了一个创建对象的接口, 但是让子类来决定具体创建的是哪一个对象. 工厂方法让一个类延迟实例化, 直到子类的出现.
• 

设计原则

• DIP (Dependency Inversion Principle) 依赖反转原则.
• 进一步解释就是: 高级别的组件不应该依赖于低级别的组件, 它们都应该依赖于抽线.