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