乐在其中设计模式(C#) - 状态模式(State Pattern).doc

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。MessageModelusingSystem;usingSystem.Collections.Generic;usingSystem.Text; namespacePattern.State/*/Message实体类/publicclassMessageModel/*/构造函数/Message内容/Message发布时间publicMessageModel(stringmsg,DateTimept)this._message=msg;this._publishTime=pt;privatestring_message;/*/Message内容/publicstringMessagegetreturn_message;set_message=value;privateDateTime_publishTime;/*/Message发布时间/publicDateTimePublishTimegetreturn_publishTime;set_publishTime=value;AbstractMessageStateusingSystem;usingSystem.Collections.Generic;usingSystem.Text; namespacePattern.State/*/状态模式抽象类/publicabstractclassAbstractMessageState/*/Context类型/protectedMessage_message;/*/Context类型属性/publicMessageMessagegetreturn_message;set_message=value;/*/改变状态/publicabstractvoidStateChangeCheck();/*/获取Message/publicabstractListGet();/*/插入Message/Message实体对象/publicabstractboolInsert(MessageModelmm);XmlMessageusingSystem;usingSystem.Collections.Generic;usingSystem.Text;namespacePattern.State/*/Xml方式操作Message/publicclassXmlMessage:AbstractMessageState/*/构造函数/Context类型参数publicXmlMessage(Messagemessage)this._message=message;/*/改变状态/publicoverridevoidStateChangeCheck()/如果UserId是admin则变换状态为SqlMessageif(this._message.UserId=admin)this._message.AbstractMessageState=newSqlMessage(this._message);/*/获取Message/publicoverrideListGet()Listl=newList();l.Add(newMessageModel(XML方式获取Message,DateTime.Now);returnl;/*/插入Message/Message实体对象/publicoverrideboolInsert(MessageModelmm)/代码略returntrue;SqlMessageusingSystem;usingSystem.Collections.Generic;usingSystem.Text;namespacePattern.State/*/Sql方式操作Message/publicclassSqlMessage:AbstractMessageState/*/构造函数/Context类型参数publicSqlMessage(Messagemessage)this._message=message;/*/改变状态/publicoverridevoidStateChangeCheck()/*/获取Message/publicoverrideListGet()Listl=newList();l.Add(newMessageModel(SQL方式获取Message,DateTime.Now);returnl;/*/插入Message/Message实体对象/publicoverrideboolInsert(MessageModelmm)/代码略returntrue;MessageusingSystem;usingSystem.Collections.Generic;usingSystem.Text;namespacePattern.State/*/Context类/publicclassMessage/*/类型为状态模式抽象类的私有变量/privateAbstractMessageState_abstractMessageState;/*/类型为状态模式抽象类的属性/publicAbstractMessageStateAbstractMessageStategetreturn_abstractMessageState;set_abstractMessageState=value;/*/UserId私有变量/privatestring_userId;/*/UserId/publicstringUserIdgetreturn_userId;set_userId=value;/*/构造函数/UserIdpublicMessage(stringuserId)this._userId=userId;_abstractMessageState=newXmlMessage(this);/*/获取Message/publicListGet()/修改状态_abstractMessageState.StateChangeCheck();return_abstractMessageState.Get();/*/插入Message/Message实体对象/publicboolInsert(MessageModelmm)/修改状态_abstractMessageState.StateChangeCheck();return_abstractMessageState.Insert(mm);clientusingSystem;usingSystem.Data;usingSystem.Configuration;usingSystem.Collections;usingSystem.Web;usingSystem.Web.Security;usingSystem.Web.UI;usingSystem.Web.UI.WebControls;usingSystem.Web.UI.WebControls.WebParts;usingSystem.Web.UI.HtmlControls;usingPattern.State;publicpartialclassState:System.Web.UI.PageprotectedvoidPage_Load(objectsender,EventArgse)Messagem=newMessage(admin);Response.Write(m.Insert(newMessageModel(插入,DateTime.Now);Response.Write();Response.Write(m.Get()0.Message+m.Get()0.PublishTime.ToString();Response.Write();m=newMessage(user);Response.Write(m.Insert(newMessageModel(插入,DateTim