了解“装饰样式”举一个真实的例子 [英] Understand the "Decorator Pattern" with a real world example

问题描述

我正在研究 href = http://en.wikipedia.org/wiki/Design_Patterns rel = noreferrer> GOF 中记录的装饰器模式。

I was studying the Decorator Pattern as documented in GOF.

请帮助我了解装饰器模式。有人可以举一个在现实世界中有用的用例示例吗？

Please, help me understand the Decorator Pattern. Could someone give a use-case example of where this is useful in the real world?

推荐答案

装饰器模式实现了将
职责动态添加到任何对象的单一目标。

考虑一下a比萨店的情况。在比萨店，他们将出售少量比萨饼品种，并且还将在菜单中提供浇头。现在想象一种情况，如果比萨店必须提供比萨饼和浇头的每种组合的价格。即使有四个基本的比萨饼和8个不同的浇头，应用程序也会疯狂地维护所有这些比萨饼和浇头的具体组合。

Consider a case of a pizza shop. In the pizza shop they will sell few pizza varieties and they will also provide toppings in the menu. Now imagine a situation wherein if the pizza shop has to provide prices for each combination of pizza and topping. Even if there are four basic pizzas and 8 different toppings, the application would go crazy maintaining all these concrete combination of pizzas and toppings.

这里是装饰器模式。

按照装饰器模式，您将实现浇头，因为装饰器和比萨饼将由这些浇头的装饰器装饰。实际上，每个客户都希望获得自己想要的浇头，最终账单金额将由基础比萨和额外订购的浇头组成。每个装饰工都会知道它要装饰的比萨饼及其价格。顶部对象的GetPrice（）方法将返回比萨饼和顶部的累计价格。

As per the decorator pattern, you will implement toppings as decorators and pizzas will be decorated by those toppings' decorators. Practically each customer would want toppings of his desire and final bill-amount will be composed of the base pizzas and additionally ordered toppings. Each topping decorator would know about the pizzas that it is decorating and it's price. GetPrice() method of Topping object would return cumulative price of both pizza and the topping.

public abstract class BasePizza
{
    protected double myPrice;

    public virtual double GetPrice()
    {
        return this.myPrice;
    }
}

public abstract class ToppingsDecorator : BasePizza
{
    protected BasePizza pizza;
    public ToppingsDecorator(BasePizza pizzaToDecorate)
    {
        this.pizza = pizzaToDecorate;
    }

    public override double GetPrice()
    {
        return (this.pizza.GetPrice() + this.myPrice);
    }
}

class Program
{
    [STAThread]
    static void Main()
    {
        //Client-code
        Margherita pizza = new Margherita();
        Console.WriteLine("Plain Margherita: " + pizza.GetPrice().ToString());

        ExtraCheeseTopping moreCheese = new ExtraCheeseTopping(pizza);
        ExtraCheeseTopping someMoreCheese = new ExtraCheeseTopping(moreCheese);
        Console.WriteLine("Plain Margherita with double extra cheese: " + someMoreCheese.GetPrice().ToString());

        MushroomTopping moreMushroom = new MushroomTopping(someMoreCheese);
        Console.WriteLine("Plain Margherita with double extra cheese with mushroom: " + moreMushroom.GetPrice().ToString());

        JalapenoTopping moreJalapeno = new JalapenoTopping(moreMushroom);
        Console.WriteLine("Plain Margherita with double extra cheese with mushroom with Jalapeno: " + moreJalapeno.GetPrice().ToString());

        Console.ReadLine();
    }
}

public class Margherita : BasePizza
{
    public Margherita()
    {
        this.myPrice = 6.99;
    }
}

public class Gourmet : BasePizza
{
    public Gourmet()
    {
        this.myPrice = 7.49;
    }
}

public class ExtraCheeseTopping : ToppingsDecorator
{
    public ExtraCheeseTopping(BasePizza pizzaToDecorate)
        : base(pizzaToDecorate)
    {
        this.myPrice = 0.99;
    }
}

public class MushroomTopping : ToppingsDecorator
{
    public MushroomTopping(BasePizza pizzaToDecorate)
        : base(pizzaToDecorate)
    {
        this.myPrice = 1.49;
    }
}

public class JalapenoTopping : ToppingsDecorator
{
    public JalapenoTopping(BasePizza pizzaToDecorate)
        : base(pizzaToDecorate)
    {
        this.myPrice = 1.49;
    }
}

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