二十四种设计模式：工厂方法模式(Factory Method Pattern)

工厂方法模式(Factory Method Pattern)

介绍
定义一个用于创建对象的接口，让子类决定将哪一个类实例化。Factory Method使一个类的实例化延迟到其子类。

示例
有SqlMessage和XmlMessage，用Factory Method来实例化它们。

　　MessageModel

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

namespace Pattern.FactoryMethod
{
    /// <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.FactoryMethod
{
    /// <summary>
    /// 操作Message抽象类（Product）
    /// </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.FactoryMethod
{
    /// <summary>
    /// Sql方式操作Message（ConcreteProduct）
    /// </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.FactoryMethod
{
    /// <summary>
    /// Xml方式操作Message（ConcreteProduct）
    /// </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;
        }
    }
}

　　AbstractMessageFactory

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

namespace Pattern.FactoryMethod
{
    /// <summary>
    /// 抽象Message工厂（Creator）
    /// </summary>
    public abstract class AbstractMessageFactory
    {
        // An Operation

        /// <summary>
        /// 工厂方法
        /// </summary>
        /// <returns>AbstractMessage</returns>
        public abstract AbstractMessage CreateMessage();
    }
}

　　SqlMessageFactory

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

namespace Pattern.FactoryMethod
{
    /// <summary>
    /// SqlMessage工厂（ConcreteCreator）
    /// </summary>
    public class SqlMessageFactory : AbstractMessageFactory
    {
        /// <summary>
        /// 实现工厂方法，返回SqlMessage对象
        /// </summary>
        /// <returns></returns>
        public override AbstractMessage CreateMessage()
        {
            return new SqlMessage();
        }
    }
}

　　XmlMessageFactory

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

namespace Pattern.FactoryMethod
{
    /// <summary>
    /// XmlMessage工厂（ConcreteCreator）
    /// </summary>
    public class XmlMessageFactory : AbstractMessageFactory
    {
        /// <summary>
        /// 实现工厂方法，返回XmlMessage对象
        /// </summary>
        /// <returns></returns>
        public override AbstractMessage CreateMessage()
        {
            return new XmlMessage();
        }
    }
}

　　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.FactoryMethod;

public partial class FactoryMethod : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        AbstractMessageFactory amf = new SqlMessageFactory();
        AbstractMessage am = amf.CreateMessage();

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

        amf = new XmlMessageFactory();
        am = amf.CreateMessage();

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

　　运行结果
　　True
　　SQL方式获取Message 2007-5-4 22:34:39
　　True
　　XML方式获取Message 2007-5-4 22:34:39