Decorator Pattern(装饰模式)

装饰模式：动态的给一个对象添加一些额外的职责。当然我们也可以通过继承来实现类似的功能，但是随着子类的增多，各种子类的组合会造成子类的急剧膨胀。

Requirement:

　　假设客户有一个要求，需要打一个report,并且report 的header 和footer 各有3种，然后要求打出所有可能组合的report。

Analysis：

　　当然纯粹的通过子类继承也可以实现，但是现在如果header 和footer各有10种呢，那么你就要有100个扩展类。但是通过使用装饰模式，你只要10 header 类+10个footer类（即20个类）就可以轻松搞定。下面我们以header 和footer 各有两个具体实现一下。

Sample Code：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TestDecoratorPatternSample
{
    public abstract class Report
    {
        public abstract void ReportContent();
    }

    public class Content : Report
    {
        public override void ReportContent()
        {
            Console.WriteLine("This is report content.");
        }
    }

    public abstract class ReportDecorator : Report
    {
        private Report report;
        public ReportDecorator(Report myReport)
        {
            report = myReport;
        }
        public override void ReportContent()
        {
            report.ReportContent();
        }
    }
    #region Header1
    public class Header1 : ReportDecorator
    {
        public Header1(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            ReportHeader();
            base.ReportContent();
        }

        public void ReportHeader()
        {
            Console.WriteLine("This is report header1.");
        }
    }

    #endregion
    #region Header2

    public class Header2 : ReportDecorator
    {
        public Header2(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            ReportHeader();
            base.ReportContent();
        }

        public void ReportHeader()
        {
            Console.WriteLine("This is report header2.");
        }
    }

    #endregion
    #region Header3

    public class Header3 : ReportDecorator
    {
        public Header3(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            ReportHeader();
            base.ReportContent();
        }

        public void ReportHeader()
        {
            Console.WriteLine("This is report header3.");
        }
    }

    #endregion
    #region Footer1
    public class Footer1 : ReportDecorator
    {
        public Footer1(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            base.ReportContent();
            ReportFooter();
        }

        public void ReportFooter()
        {
            Console.WriteLine("This is report Footer1.");
        }
    }
    #endregion
    #region Footer2

    public class Footer2 : ReportDecorator
    {
        public Footer2(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            base.ReportContent();
            ReportFooter();
        }

        public void ReportFooter()
        {
            Console.WriteLine("This is report Footer2.");
        }
    }

    #endregion
    #region Footer3

    public class Footer3 : ReportDecorator
    {
        public Footer3(Report myReport)
            : base(myReport)
        {
        }

        public override void ReportContent()
        {
            base.ReportContent();
            ReportFooter();
        }

        public void ReportFooter()
        {
            Console.WriteLine("This is report Footer3.");
        }
    }

    #endregion
}

　　下面是客户端的调用代码，你需要怎么组合在你调用的时候就怎么组合。

            Content clientReport = new Content();
            Report header2 = new Header2(clientReport);
            Report footer1 = new Footer1(header2);
            footer1.ReportContent();

　　

欢迎各位网友拍砖，本人也在不断学习中。。。