结构型设计模式之装饰模式

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。

 1 using System;
 2
 3     abstract class Component
 4     {
 5         public abstract void Draw();
 6     }
 7
 8     class ConcreteComponent : Component
 9     {
10         private string strName;
11         public ConcreteComponent(string s)
12         {
13             strName = s;
14         }
15
16         public override void Draw()
17         {
18             Console.WriteLine("ConcreteComponent - {0}", strName);
19         }
20     }
21
22     abstract class Decorator : Component
23     {
24         protected Component ActualComponent;
25
26         public void SetComponent(Component c)
27         {
28             ActualComponent = c;
29         }
30         public override void Draw()
31         {
32             if (ActualComponent != null)
33                 ActualComponent.Draw();
34         }
35     }
36
37     class ConcreteDecorator : Decorator
38     {
39         private string strDecoratorName;
40         public ConcreteDecorator (string str)
41         {
42             // how decoration occurs is localized inside this decorator
43             // For this demo, we simply print a decorator name
44             strDecoratorName = str;
45         }
46         public override void Draw()
47         {
48             CustomDecoration();
49             base.Draw();
50         }
51         void CustomDecoration()
52         {
53             Console.WriteLine("In ConcreteDecorator: decoration goes here");
54             Console.WriteLine("{0}", strDecoratorName);
55         }
56     }
57
58
59     /// <summary>
60     ///    Summary description for Client.
61     /// </summary>
62     public class Client
63     {
64         Component Setup()
65         {
66             ConcreteComponent c = new ConcreteComponent("This is the real component");
67
68             ConcreteDecorator d = new ConcreteDecorator("This is a decorator for the component");
69
70             d.SetComponent(c);
71
72             return d;
73         }
74
75         public static int Main(string[] args)
76         {
77             Client client = new Client();
78             Component c = client.Setup();
79
80             // The code below will work equally well with the real component,
81             // or a decorator for the component
82
83             c.Draw();
84
85             return 0;
86         }
87     }

装饰模式