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

OK
[源码下载]

本文转自webabcd 51CTO博客，原文链接：http://blog.51cto.com/webabcd/344585，如需转载请自行联系原作者