二十四种设计模式：策略模式(Strategy Pattern)

策略模式(Strategy Pattern)

介绍
定义一系列的算法，把它们一个个封装起来，并且使它们可相互替换。本模式使得算法的变化可独立于使用它的客户。

示例
有一个Message实体类，对它的操作有Insert()和Get()方法，持久化数据在SqlServer数据库中或Xml文件里（两种可互换的算法）。由客户端决定使用哪种算法。

　　MessageModel

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

namespace Pattern.Strategy
{
    /// <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; }
        }
    }
}

　　IMessageStrategy

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

namespace Pattern.Strategy
{
    /// <summary>
    /// 策略接口
    /// </summary>
    public interface IMessageStrategy
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        List<MessageModel> Get();

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

　　SqlMessage

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

namespace Pattern.Strategy
{
    /// <summary>
    /// Sql方式操作Message
    /// </summary>
    public class SqlMessage : IMessageStrategy
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public 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 bool Insert(MessageModel mm)
        {
            // 代码略
            return true;
        }
    }
}

　　XmlMessage

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

namespace Pattern.Strategy
{
    /// <summary>
    /// Xml方式操作Message
    /// </summary>
    public class XmlMessage : IMessageStrategy
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public 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 bool Insert(MessageModel mm)
        {
            // 代码略
            return true;
        }
    }
}

　　Message

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

namespace Pattern.Strategy
{
    /// <summary>
    /// Context类
    /// </summary>
    public class Message
    {
        /// <summary>
        /// 声明一个IMessageStrategy类型
        /// </summary>
        private IMessageStrategy _strategy;

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="strategy">具体算法</param>
        public Message(IMessageStrategy strategy)
        {
            this._strategy = strategy;
        }

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

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

　　Client

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.Strategy;

public partial class Strategy : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Message m = new Message(new XmlMessage());
        Response.Write(m.Insert(new MessageModel("插入", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());
        Response.Write("<br />");

        m = new Message(new SqlMessage());
        Response.Write(m.Insert(new MessageModel("插入", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());
        Response.Write("<br />");
    }
}

　　运行结果

　　True
　　XML方式获取Message 2007-2-10 22:42:44
　　True
　　SQL方式获取Message 2007-2-10 22:42:44