第十四章 Caché 设计模式 备忘录模式

定义

在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可将该对象回复到原先保存的状态。

使用场景

• 备忘录模式比较适用于功能比较复杂的，但需要维护或记录属性历史的类，或者需要保存的属性只是众多属性中的一小部分时，Originator可以根据保存的Memento信息还原到前一状态。
• 如果在某个系统中使用命令模式时，需要实现命令的撤销功能，那么命令模式可以使用备忘录模式来储存可撤销操作的状态。
• 当角色的状态改变的时候，有可能在这个状态无效，这时候就可以使用暂时储存起来的备忘录将状态复原。

结构图

描述

玩游戏时，角色有体力值，攻击力，防御力。保存这些状态并恢复。

完整示例

角色类

Class PHA.YX.Design.Memento.GameRole Extends %RegisteredObject {  Property vitality As %Integer [ Private ];  Method vitalityGet() As %Integer [ ServerOnly = 1 ] {  Quit i%vitality }  Method vitalitySet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%vitality = Arg  Quit $$$OK }  Property attact As %Integer [ Private ];  Method attactGet() As %Integer [ ServerOnly = 1 ] {  Quit i%attact }  Method attactSet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%attact = Arg  Quit $$$OK }  Property defense As %Integer [ Private ];  Method defenseGet() As %Integer [ ServerOnly = 1 ] {    Quit i%defense }  Method defenseSet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%defense = Arg  Quit $$$OK }  Method StateDisplay() {  w "当前角色状态：",!  w "体力：" _ ..vitalityGet(),!  w "攻击力：" _ ..attactGet(),!  w "防御力：" _ ..defenseGet(),!  w "",! }  Method GetInitState() {  s ..vitality = 100  s ..attact = 100  s ..defense = 100 }  Method Fight() {  s ..vitality = 0  s ..attact = 0  s ..defense = 0 }  Method SaveState() As RoleStateMemento {  q ##class(RoleStateMemento).%New(..vitality, ..attact, ..defense) }  Method RecoveryState(memento As RoleStateMemento) {  s ..vitality = memento.vitalityGet()  s ..attact = memento.attactGet()  s ..defense = memento.defenseGet() }  }  

储存类

Class PHA.YX.Design.Memento.RoleStateMemento Extends %RegisteredObject {  Property vitality As %Integer [ Private ];  Method vitalityGet() As %Integer [ ServerOnly = 1 ] {  Quit i%vitality }  Method vitalitySet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%vitality = Arg  Quit $$$OK }  Property attact As %Integer [ Private ];  Method attactGet() As %Integer [ ServerOnly = 1 ] {  Quit i%attact }  Method attactSet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%attact = Arg  Quit $$$OK }  Property defense As %Integer [ Private ];  Method defenseGet() As %Integer [ ServerOnly = 1 ] {    Quit i%defense }  Method defenseSet(Arg As %Integer) As %Status [ ServerOnly = 1 ] {  s i%defense = Arg  Quit $$$OK }  Method %OnNew(vitality, attact, defense) As %Status [ Private, ServerOnly = 1 ] {  s ..vitality = vitality  s ..attact = attact  s ..defense = defense  Quit $$$OK }  }  

管理类

Class PHA.YX.Design.Memento.RoleStateCaretaker Extends %RegisteredObject {  Property memento As RoleStateMemento [ Private ];  Method mementoGet() As RoleStateMemento [ ServerOnly = 1 ] {  Quit i%memento }  Method mementoSet(Arg As RoleStateMemento) As %Status [ ServerOnly = 1 ] {  s i%memento = Arg  Quit $$$OK }  }  

调用

/// d ##class(PHA.YX.Design.Program).Memento()  ClassMethod Memento() {  /*进入游戏*/  #dim yx as PHA.YX.Design.Memento.GameRole  s yx = ##class(PHA.YX.Design.Memento.GameRole).%New()  d yx.GetInitState()  d yx.StateDisplay()    /*保存进度*/  #dim state as PHA.YX.Design.Memento.RoleStateCaretaker  s state = ##class(PHA.YX.Design.Memento.RoleStateCaretaker).%New()  d state.mementoSet(yx.SaveState())    /*大战BOSS，损耗严重*/  d yx.Fight()  d yx.StateDisplay()    /*恢复之前状态*/  d yx.RecoveryState(state.mementoGet())  d yx.StateDisplay() } 

DHC-APP>d ##class(PHA.YX.Design.Program).Memento() 当前角色状态： 体力：100 攻击力：100 防御力：100   当前角色状态： 体力：0 攻击力：0 防御力：0   当前角色状态： 体力：100 攻击力：100 防御力：100 

思考

记录听歌时的状态（歌曲名称，百分比，播放模式）。感兴趣的同学实现后可以发我一起参考下。