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。。。