作用:
在不破壞封裝性的前提下,捕獲一個對象的內部狀態,并在該對象之外保存這個狀態.這樣以后就可將該對象恢復到原先保存的狀態.
UML結構圖:
解析:
Memento模式中封裝的是需要保存的狀態,當需要恢復的時候才取出來進行恢復.原理很簡單,實現的時候需要注意一個地方:窄接口和寬接口.所謂的寬接口就是一般意義上的接口,把對外的接口作為public成員;而窄接口反之,把接口作為private成員,而把需要訪問這些接口函數的類作為這個類的友元類,也就是說接口只暴露給了對這些接口感興趣的類,而不是暴露在外部.下面的實現就是窄實現的方法來實現的.
實現:
1)Memento.h
/**//********************************************************************
????created:????2006/08/09
????filename:?????Memento.h
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Memento模式的演示代碼
*********************************************************************/
#ifndef?MEMENTO_H
#define?MEMENTO_H
#include?<string>
typedef?std::string?State;
class?Memento;
class?Originator
{
public:
????Originator(const?State&?rState);
????Originator();
????~Originator();
????Memento*????CreateMemento();
????void????????SetMemento(Memento*?pMemento);
????State????????GetState();
????void????????SetState(const?State&?rState);
????void????????RestoreState(Memento*?pMemento);
????void????????PrintState();
private:
????State????????m_State;
};
//?把Memento的接口函數都設置為私有的,而Originator是它的友元,
//?這樣保證了只有Originator可以對其訪問
class?Memento
{
private:
????friend?class?Originator;
????Memento(const?State&?rState);
????void????SetState(const?State&?rState);
????State????GetState();
????State????m_State;
};
#endif
2)Memento.cpp
/**//********************************************************************
????created:????2006/08/09
????filename:?????Memento.cpp
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Memento模式的演示代碼
*********************************************************************/
#include?"Memento.h"
#include?<iostream>
Originator::Originator()
{
}
Originator::Originator(const?State&?rState)
????:?m_State(rState)
{
}
Originator::~Originator()
{
}
State?Originator::GetState()
{
????return?m_State;
}
void?Originator::SetState(const?State&?rState)
{
????m_State?=?rState;
}
Memento*?Originator::CreateMemento()
{
????return?new?Memento(m_State);
}
void?Originator::RestoreState(Memento*?pMemento)
{
????if?(NULL?!=?pMemento)
????{
????????m_State?=?pMemento->GetState();
????}????
}
void?Originator::PrintState()
{
????std::cout?<<?"State?=?"?<<?m_State?<<?std::endl;
}
Memento::Memento(const?State&?rState)
????:?m_State(rState)
{
}
State?Memento::GetState()
{
????return?m_State;
}
void?Memento::SetState(const?State&?rState)
{
????m_State?=?rState;
}
3)Main.cpp
/**//********************************************************************
????created:????2006/08/09
????filename:?????Main.cpp
????author:????????李創
????????????????http://www.shnenglu.com/converse/
????purpose:????Memento模式的測試代碼
*********************************************************************/
#include?"Memento.h"
int?main()
{
????//?創建一個原發器
????Originator*?pOriginator?=?new?Originator("old?state");
????pOriginator->PrintState();
????//?創建一個備忘錄存放這個原發器的狀態
????Memento?*pMemento?=?pOriginator->CreateMemento();
????
????//?更改原發器的狀態
????pOriginator->SetState("new?state");
????pOriginator->PrintState();
????//?通過備忘錄把原發器的狀態還原到之前的狀態
????pOriginator->RestoreState(pMemento);
????pOriginator->PrintState();
????delete?pOriginator;
????delete?pMemento;
????return?0;
}