设计模式-结构型-装饰模式

装饰模式 Decorator

结构： 意图：

动态的给一个对象添加一些额外的职责。就增加功能来说，Decorator模式相比生成子类更为灵活。

适用性：

l  在不影响其它对象的情况下，以动态、透明的方式给单个对象添加职责。

l  处理那些可以撤销的职责。

l  当不能以生成子类的方法进行扩充时。

n  一种情况是，可能有大量独立的扩展，为支持每一种组合将产生大量的子类，使得子类数目呈爆炸性增长。

n  另一种情况可能是因为类定义被隐藏，或类定义不能用于生成子类。

示例：

// Decorator


// Intent: "Attach additional responsibilites to an object dynamically.

// Decorators provide a flexible alternative to subclassing for

// extending functionality".

//动态地给一个对象添加一些额外的职责，就增加功能来说，装饰模式较之于子类提供了一种更加灵活的方式。

// For further information, read "Design Patterns", p175, Gamma et al.,

// Addison-Wesley, ISBN:0-201-63361-2


/* Notes:
 * Dynamically wrap functionality with additonal functionality, so that
 * the client does not know the difference.
 */

namespace Decorator_DesignPattern
{
    using System;

    abstract class Component
    {
        public abstract void Draw();
    }

    class ConcreteComponent : Component
    {
        private string strName;
        public ConcreteComponent(string s)
        {
            strName = s;
        }

        public override void Draw()
        {
            Console.WriteLine("ConcreteComponent - {0}", strName);
        }
    }

    abstract class Decorator : Component
    {
        protected Component ActualComponent;

        public void SetComponent(Component c)
        {
            ActualComponent = c;
        }
        public override void Draw()
        {
            if (ActualComponent != null)
                ActualComponent.Draw();
        }
    }

    class ConcreteDecorator : Decorator
    {
        private string strDecoratorName;
        public ConcreteDecorator(string str)
        {
            // how decoration occurs is localized inside this decorator

            // For this demo, we simply print a decorator name

            strDecoratorName = str;
        }
        public override void Draw()
        {
            CustomDecoration();
            base.Draw();
        }
        void CustomDecoration()
        {
            Console.WriteLine("In ConcreteDecorator: decoration goes here");
            Console.WriteLine("{0}", strDecoratorName);
        }
    }


    ///

    /// Summary description for Client.

    ///

    public class Client
    {
        Component Setup()
        {
            ConcreteComponent c = new ConcreteComponent("This is the real component");

            ConcreteDecorator d = new ConcreteDecorator("This is a decorator for the component");

            d.SetComponent(c);

            return d;
        }

        public static int Main(string[] args)
        {
            Client client = new Client();
            Component c = client.Setup();

            // The code below will work equally well with the real component,

            // or a decorator for the component


            c.Draw();
            Console.Read();
            return 0;
        }
    }
}