二十四种设计模式：装饰模式(Decorator Pattern)

装饰模式(Decorator Pattern)

介绍
动态地给一个对象添加一些额外的职责。就扩展功能而言，它比生成子类方式更为灵活。

示例
有一个Message实体类，某个对象对它的操作有Insert()和Get()方法，现在扩展这个对象的功能。

　　MessageModel

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// Message实体类
    /// </summary>
    public class MessageModel
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="msg">Message内容</param>
        /// <param name="pt">Message发布时间</param>
        public MessageModel(string msg, DateTime pt)
        {
            this._message = msg;
            this._publishTime = pt;
        }

        private string _message;
        /// <summary>
        /// Message内容
        /// </summary>
        public string Message
        {
            get { return _message; }
            set { _message = value; }
        }

        private DateTime _publishTime;
        /// <summary>
        /// Message发布时间
        /// </summary>
        public DateTime PublishTime
        {
            get { return _publishTime; }
            set { _publishTime = value; }
        }
    }
}

　　AbstractMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// 操作Message的抽象构件（Component）
    /// </summary>
    public abstract class AbstractMessage
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public abstract List<MessageModel> Get();

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public abstract bool Insert(MessageModel mm);
    }
}

　　SqlMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// Sql方式操作Message（ConcreteComponent）
    /// </summary>
    public class SqlMessage : AbstractMessage
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public override List<MessageModel> Get()
        {
            List<MessageModel> l = new List<MessageModel>();
            l.Add(new MessageModel("SQL方式获取Message", DateTime.Now));

            return l;
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public override bool Insert(MessageModel mm)
        {
            // 代码略
            return true;
        }
    }
}

　　XmlMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// Xml方式操作Message（ConcreteComponent）
    /// </summary>
    public class XmlMessage : AbstractMessage
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public override List<MessageModel> Get()
        {
            List<MessageModel> l = new List<MessageModel>();
            l.Add(new MessageModel("XML方式获取Message", DateTime.Now));

            return l;
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public override bool Insert(MessageModel mm)
        {
            // 代码略
            return true;
        }
    }
}

　　AbstractMessageWrapper

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// 装饰AbstractMessage（Decorator）
    /// </summary>
    public abstract class AbstractMessageWrapper : AbstractMessage
    {
        private AbstractMessage _abstractMessage;

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="abstractMessage">AbstractMessage</param>
        public AbstractMessageWrapper(AbstractMessage abstractMessage)
        {
            this._abstractMessage = abstractMessage;
        }

        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public override List<MessageModel> Get()
        {
            return _abstractMessage.Get();
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public override bool Insert(MessageModel mm)
        {
            return _abstractMessage.Insert(mm);
        }
    }
}

　　CheckUserWrapper

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// 扩展出用户验证的功能（ConcreteDecorator）
    /// </summary>
    public class CheckUserWrapper : AbstractMessageWrapper
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="abstractMessage">AbstractMessage</param>
        public CheckUserWrapper(AbstractMessage abstractMessage)
            : base(abstractMessage)
        {

        }

        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public override List<MessageModel> Get()
        {
            List<MessageModel> l = base.Get();

            foreach (MessageModel mm in l)
            {
                mm.Message += "（经过用户验证）";
            }

            return l;
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public override bool Insert(MessageModel mm)
        {
            // 在这里扩展功能

            return base.Insert(mm);
        }

    }
}

　　CheckInputWrapper

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Decorator
{
    /// <summary>
    /// 扩展出输入验证的功能（ConcreteDecorator）
    /// </summary>
    public class CheckInputWrapper : AbstractMessageWrapper
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="abstractMessage">AbstractMessage</param>
        public CheckInputWrapper(AbstractMessage abstractMessage)
            : base(abstractMessage)
        {

        }

        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public override List<MessageModel> Get()
        {
            List<MessageModel> l = base.Get();

            foreach (MessageModel mm in l)
            {
                mm.Message += "（经过输入验证）";
            }

            return l;
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public override bool Insert(MessageModel mm)
        {
            // 在这里扩展功能

            return base.Insert(mm);
        }
    }
}

　　Test

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Pattern.Decorator;

public partial class Decorator : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        AbstractMessage message = new SqlMessage();

        AbstractMessageWrapper amr = new CheckUserWrapper(message);

        Response.Write(amr.Get()[0].Message + " " + amr.Get()[0].PublishTime.ToString());
        Response.Write("<br />");

        AbstractMessageWrapper amr2 = new CheckInputWrapper(message);

        Response.Write(amr2.Get()[0].Message + " " + amr2.Get()[0].PublishTime.ToString());
        Response.Write("<br />");

        AbstractMessageWrapper amr3 = new CheckUserWrapper(message);
        AbstractMessageWrapper amr4 = new CheckInputWrapper(amr3);

        Response.Write(amr4.Get()[0].Message + " " + amr4.Get()[0].PublishTime.ToString());
        Response.Write("<br />");
    }
}

　　运行结果
　　SQL方式获取Message（经过用户验证） 2007-5-13 19:34:01
　　SQL方式获取Message（经过输入验证） 2007-5-13 19:34:01
　　SQL方式获取Message（经过用户验证）（经过输入验证） 2007-5-13 19:34:01