乐在其中设计模式(C#) - 状态模式(State Pattern)

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乐在其中设计模式(C#) - 状态模式(State Pattern)

作者： webabcd


介绍
允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它所属的类。


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。在对象内部可以根据用户的不同选择不同的数据持久化方案。

 

MessageModel

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

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

 

AbstractMessageState

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

namespace Pattern.State
{
         /// <summary>
         /// 状态模式抽象类
         /// </summary>
         public abstract class AbstractMessageState
        {
                 /// <summary>
                 /// Context类型
                 /// </summary>
                 protected Message _message;

                 /// <summary>
                 /// Context类型属性
                 /// </summary>
                 public Message Message
                {
                        get { return _message; }
                        set { _message = value; }
                }

                 /// <summary>
                 /// 改变状态
                 /// </summary>
                 public abstract void StateChangeCheck();

                 /// <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);
        }
}

 

XmlMessage

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

namespace Pattern.State
{
         /// <summary>
         /// Xml方式操作Message
         /// </summary>
         public class XmlMessage : AbstractMessageState
        {
                 /// <summary>
                 /// 构造函数
                 /// </summary>
                 /// <param name="message">Context类型参数</param>
                 public XmlMessage(Message message)
                {
                         this._message = message;
                }

                 /// <summary>
                 /// 改变状态
                 /// </summary>
                 public override void StateChangeCheck()
                {
                         // 如果UserId是admin则变换状态为SqlMessage
                         if ( this._message.UserId == "admin")
                        {
                                 this._message.AbstractMessageState = new SqlMessage( this._message);
                        }
                }

                 /// <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;
                }
        }
}

 

SqlMessage

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

namespace Pattern.State
{
         /// <summary>
         /// Sql方式操作Message
         /// </summary>
         public class SqlMessage : AbstractMessageState
        {
                 /// <summary>
                 /// 构造函数
                 /// </summary>
                 /// <param name="message">Context类型参数</param>
                 public SqlMessage(Message message)
                {
                         this._message = message;
                }

                 /// <summary>
                 /// 改变状态
                 /// </summary>
                 public override void StateChangeCheck()
                {

                }

                 /// <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;
                }
        }
}

 

Message

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

namespace Pattern.State
{
         /// <summary>
         /// Context类
         /// </summary>
         public class Message
        {
                 /// <summary>
                 /// 类型为状态模式抽象类的私有变量
                 /// </summary>
                 private AbstractMessageState _abstractMessageState;

                 /// <summary>
                 /// 类型为状态模式抽象类的属性
                 /// </summary>
                 public AbstractMessageState AbstractMessageState
                {
                        get { return _abstractMessageState; }
                        set { _abstractMessageState = value; }
                }                

                 /// <summary>
                 /// UserId私有变量
                 /// </summary>
                 private string _userId;

                 /// <summary>
                 /// UserId
                 /// </summary>
                 public string UserId
                {
                        get { return _userId; }
                        set { _userId = value; }
                }

                 /// <summary>
                 /// 构造函数
                 /// </summary>
                 /// <param name="userId">UserId</param>
                 public Message( string userId)
                {
                         this._userId = userId;

                        _abstractMessageState = new XmlMessage( this);
                }

                 /// <summary>
                 /// 获取Message
                 /// </summary>
                 /// <returns></returns>
                 public List<MessageModel> Get()
                {
                         // 修改状态
                        _abstractMessageState.StateChangeCheck();

                         return _abstractMessageState.Get();
                }

                 /// <summary>
                 /// 插入Message
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 /// <returns></returns>
                 public bool Insert(MessageModel mm)
                {
                         // 修改状态
                        _abstractMessageState.StateChangeCheck();

                         return _abstractMessageState.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.State;

public partial class State : System.Web.UI.Page
{
         protected void Page_Load( object sender, EventArgs e)
        {
                Message m = new Message( "admin");
                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( "user");
                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
SQL方式获取Message 2007-3-6 22:58:17
True
XML方式获取Message 2007-3-6 22:58:17


参考
http://www.dofactory.com/Patterns/PatternState.aspx


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转载于:https://blog.51cto.com/webabcd/344585