问题描述
我想知道如何将状态添加到消费者可用的装饰器链中。给定这个简化的模型:
c> MetricSizePizzaDecorator ,将尺寸转换为英制/公制单位。客户端不会知道比萨已经被装饰 - 它只是调用 getSize(),并且对结果进行任何处理(例如计算价格)。
我可能不会在我的例子中使用装饰器,但关键是:它不会改变界面。事实上,几乎所有的设计模式都归结为这样 - 在不改变界面的情况下增加设计的变化性。
I wonder how to add state to the chain of decorators that will be available to the consumer. Given this simplified model:
abstract class AbstractPizza{ public abstract print(...); } class Pizza:AbstractPizza{ public int Size (get; set;) public print(...); } abstract class AbstractPizzaDecorator{ public Pizza:AbstractPizza; public abstract print(); } class HotPizzaDecorator:AbstractPizzaDecorator{ public int Hotness (get; set;) public print(...); } class CheesyPizzaDecorator:AbstractPizzaDecorator{ public string Cheese (get; set;) public print(...); } void Main() { BigPizza = new Pizza(); BigPizza.Size = 36; HotBigPizza = new HotPizzaDecorator(); HotBigPizza.Pizza = BigPizza; HotBigPizza.Hotness = 3; HotBigCheesyPizza = new CheesyPizzaDecorator(); HotBigCheesyPizza.Pizza = HotBigPizza; HotBigCheesyPizza.Cheese = "Blue"; HotBigCheesyPizza.print(); HotBigCheesyPizza.size = 28; //ERRRRRR !!!!!!!!!!!!!!!!!!!!!!! }Now if they all implement the print method and propagate that though the chain, it's all good. But how does that work for the state? I can't access the size property on the HotBigCheesyPizza.
What's the part that I'm missing? Wrong pattern?
Thanks for helping!Cheers
解决方案The decorator pattern is for adding additional behavior to the decorated class without the client needing to adjust. Thus it is not intended for adding a new interface (e.g. hotness, cheese) to the thing being decorated.
A somewhat bad example of what it might be used for is where you want to change how size is calculated: you could create a MetricSizePizzaDecorator that converts the size to/from English/metric units. The client would not know the pizza has been decorated - it just calls getSize() and does whatever it needs to do with the result (for example, to calculate the price).
I would probably not use the decorator in my example, but the point is: it does not alter the interface. In fact, nearly all design patterns come down to that - adding variability to a design without changing interfaces.
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