decorator - 通过实际示例了解 "Decorator Pattern"

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我正在研究装饰器模式，如 GOF 中所述.

请帮助我理解装饰器模式。有人可以举一个用例来说明这在现实世界中有用吗？

Answer 1

Decorator pattern achieves a single objective of dynamically addingresponsibilities to any object.

考虑一个披萨店的例子。在披萨店里，他们会出售几种披萨品种，并且还会在菜单中提供配料。现在想象一下这样一种情况，如果披萨店必须提供披萨和配料的每种组合的价格。即使有四种基本的披萨和 8 种不同的配料，应用程序也会疯狂地维护所有这些披萨和配料的具体组合。

这里是装饰器模式。

根据装饰器模式，您将实现配料作为装饰器，而披萨将由这些配料的装饰器装饰。实际上，每个顾客都会想要他想要的配料，最终的账单金额将由基础披萨和额外订购的配料组成。每个配料装饰师都会知道其正在装饰的比萨饼及其价格。 Topping 对象的 GetPrice() 方法将返回披萨和配料的累计价格。

编辑

这是上面解释的代码示例。

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;
    }
}