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{    /// 
    /// Message实体类    /// 
    public class MessageModel    {        /// 
        /// 构造函数        /// 
        /// Message内容        /// Message发布时间        public MessageModel(string msg, DateTime pt)        {            this._message = msg;            this._publishTime = pt;        }        private string _message;        /// 
        /// Message内容        /// 
        public string Message        {            get { return _message; }            set { _message = value; }        }        private DateTime _publishTime;        /// 
        /// Message发布时间        /// 
        public DateTime PublishTime        {            get { return _publishTime; }            set { _publishTime = value; }        }    }}

　　IMessageStrategy

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Strategy{    /// 
    /// 策略接口    /// 
    public interface IMessageStrategy    {        /// 
        /// 获取Message        /// 
        /// 
             List
     
       Get();        /// 
      
        /// 插入Message        /// 
        /// 
      Message实体对象        /// 
              bool Insert(MessageModel mm);    }}
     

　　SqlMessage

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Strategy{    /// 
    /// Sql方式操作Message    /// 
    public class SqlMessage : IMessageStrategy    {        /// 
        /// 获取Message        /// 
        /// 
             public List
     
       Get()        {            List
      
        l = new List
       
        ();            l.Add(new MessageModel("SQL方式获取Message", DateTime.Now));            return l;        }        /// 
        
        /// 插入Message        /// 
        /// 
        Message实体对象        /// 
                public bool Insert(MessageModel mm)        {            // 代码略            return true;        }    }}
       
      
     

　　XmlMessage

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Strategy{    /// 
    /// Xml方式操作Message    /// 
    public class XmlMessage : IMessageStrategy    {        /// 
        /// 获取Message        /// 
        /// 
             public List
     
       Get()        {            List
      
        l = new List
       
        ();            l.Add(new MessageModel("XML方式获取Message", DateTime.Now));            return l;        }        /// 
        
        /// 插入Message        /// 
        /// 
        Message实体对象        /// 
                public bool Insert(MessageModel mm)        {            // 代码略            return true;        }    }}
       
      
     

　　Message

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Strategy{    /// 
    /// Context类    /// 
    public class Message    {        /// 
        /// 声明一个IMessageStrategy类型        /// 
        private IMessageStrategy _strategy;        /// 
        /// 构造函数        /// 
        /// 具体算法        public Message(IMessageStrategy strategy)        {            this._strategy = strategy;        }        /// 
        /// 获取Message        /// 
        /// 
             public List
     
       Get()        {            return _strategy.Get();        }        /// 
      
        /// 插入Message        /// 
        /// 
      Message实体对象        /// 
              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("
");        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());        Response.Write("
");        m = new Message(new SqlMessage());        Response.Write(m.Insert(new MessageModel("插入", DateTime.Now)));        Response.Write("
");        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());        Response.Write("
");    }}

　　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