即在不改变类本身，动态地扩展对象的功能。它是通过创建一个包装对象，也就是装饰来包裹真实的对象。包装对象和原对象拥有相似的接口方法（功能）。
public class OrderInfo
{
/// <summary>
/// 下单时间
/// </summary>
public DateTime CreateTime{get;set;}
/// <summary>
/// 等级
/// </summary>
public int Level{get;set;}
}
public abstract class OrderManager
{
public abstract void Summit(OrderInfo order);
public abstract void CancelOrder(OrderInfo order);
}
public class SimpleOrderManager : OrderManager
{
public override void Summit(OrderInfo order)
{
//TODO summit the order
Console.WriteLine("Summit the order");
}
public override void CancelOrder(OrderInfo order)
{
//TODO cancel the order
Console.WriteLine("cancel the order");
}
}
/// <summary>
///
/// </summary>
public class OrderManagerDecorator : OrderManager
{
private OrderManager orderManager = null;
public OrderManagerDecorator(OrderManager orderManager)
{
this.orderManager = orderManager;
}
public override void Summit(OrderInfo order)
{
orderManager.Summit(order);
}
public override void CancelOrder(OrderInfo order)
{
orderManager.CancelOrder(order);
}
}
public class ForeignOrderManager : OrderManagerDecorator
{
public ForeignOrderManager(OrderManager orderManager):base(orderManager)
{
}
public override void Summit(OrderInfo order)
{
if (ValidateOrder(order))
{
base.Summit(order);
}
else
{
throw new Exception("the level of the order is disable");
}
}
public bool ValidateOrder(OrderInfo order)
{
//TODO validate the order
bool result = order.Level > 2;
return result;
}
public override void CancelOrder(OrderInfo order)
{
base.CancelOrder(order);
}
}
public class SuperOrderManager : OrderManagerDecorator
{
public SuperOrderManager(OrderManager orderManager)
: base(orderManager)
{
}
public override void Summit(OrderInfo order)
{
base.Summit(order);
}
public override void CancelOrder(OrderInfo order)
{
base.CancelOrder(order);
}
private bool CheckOrder(OrderInfo order)
{
if (order.CreateTime.AddDays(3) < DateTime.Now)
{
return false;
}
else
{
return true;
}
}
}
曾经以为装饰模式和组合模式很像！只是因为他们他们都包含需要包装的对象。而后来想想，才知道他们本质上差别很大：组合模式在于组合，是多个对象组合成合成的对象，合成对象可以去触发控制其包含的对象。装饰者模式则是对类本身功能的扩展，从代码上看，他是包含单个包装对象。
在编程中非常经典的使用就是Stream类型对象的构造了。主要包括FileSteam，BufferdStream等。
最后在画一幅图说明装饰模式调用的样式------实现装饰功能本身的扩展
原文：http://www.cnblogs.com/Joy-et/p/4841709.html