结构型设计模式之装饰模式(Decorator)

结构
意图	动态地给一个对象添加一些额外的职责。就增加功能来说，D e c o r a t o r 模式相比生成子类更为灵活。
适用性	在不影响其他对象的情况下，以动态、透明的方式给单个对象添加职责。 处理那些可以撤消的职责。 当不能采用生成子类的方法进行扩充时。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。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。

 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>
     ///    Summary description for Client.
     /// </summary>
     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();

             return ;
         }
     }

装饰模式