设计模式 - State Pattern(状态模式)
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
