Decorator Pattern属于Structural Patterns

介绍：

Decorator pattern的作用是提供一种方式动态的给一个对象添加新的职责或状态，被装饰的对象并不知道被“装饰”了。A key implementation point in the Decorator pattern is that decorators both inherit the original class and contain an instantiation of it.

实现：

UML 类图

    public interface IComponent
    {
        string Operation();
    }
    /// <summary>
    /// 被装饰者
    /// </summary>
    public class Component : IComponent
    {
        #region IComponent Members
        public string Operation()
        {
            return "I'm a photo;";
        }
        #endregion
    }
    /// <summary>
    /// 装饰者A
    /// </summary>
    public class DecoratorA : IComponent
    {
        IComponent component;
        public DecoratorA(IComponent component)
        {
            this.component = component;
        }
        #region IComponent Members
        public string Operation()
        {
            return component.Operation() + "and decorated by DecoratorA";
        }
        #endregion
    }
    /// <summary>
    /// 装饰者B
    /// </summary>
    public class DecoratorB : IComponent
    {
        IComponent component;
        public string AddedState = " and added state";
        public DecoratorB(IComponent component)
        {
            this.component = component;
        }
        #region IComponent Members
        public string Operation()
        {
            return component.Operation() + "and decorated by DecoratorB";
        }
        public string AddedBehavior()
        {
            return " and added behavior by DecoratorB";
        }
        #endregion
    }
    public class Client
    {
        public static void Display(string s, IComponent component)
        {
            Console.WriteLine(s + component.Operation());
        }
    }
    [TestFixture]
    public class DecoratorTest
    {
        [Test]
        public void T1()
        {
            var component = new Component();
            Client.Display(string.Empty, component);
            var decoratorB = new DecoratorB(component);
            Client.Display("hello!", decoratorB);
        }
    }