狀態模式----C++實現

標籤：

狀態模式

定義：

允許一個對象在其內部狀態改變時改變它的行為。對象看起來似乎修改了它的類。

實用性：

1、 一個對象的行為取決於它的狀態，並且它必須在運行時刻根據狀態改變它的行為。

2、 一個操作中含有龐大的多分支條件陳述式，且這些分支依賴於該對象的狀態。

 

優點：

1、 將與特定狀態相關的行為局部化，並且將不同狀態的行為分割開來。

2、 使得狀態轉換顯示化。

3、 狀態物件可以被共用。

 

結構：

實現：

 

class Context;

 

class State

{

public:

State(string name):m_name(name)

{ }

virtual void Handle(Context *pContext)

{ }

 

virtual~State()

{ }

string GetStateName()

{

returnm_name;

}

protected:

voidChangeState(Context *pContext,State *pState);

private:

string m_name;

};

 

class Context

{

public:

voidRequest()

{

m_pCurrentState->Handle(this);

}

 

voidSetCurrentState(State *pState)

{

cout<<"設定目前狀態為 :"<GetStateName()<<endl;< p="">

m_pCurrentState = pState;

}

 

State *GetCurrentState()

{

cout<<"目前狀態為 :"<<m_pcurrentstate->GetStateName()<<endl;< p="">

returnm_pCurrentState;

}

 

protected:

friend class State;

void ChangeState(State *pState)

{

cout<<"目前狀態由 : "<<m_pcurrentstate->GetStateName()<<" 轉變為狀態："<GetStateName()<<endl;< p="">

m_pCurrentState = pState;

}

private:

State *m_pCurrentState;

};

 

voidState::ChangeState(Context *pContext,State *pState)

{

pContext->ChangeState(pState);

}

 

//狀態子類可以共用，所以用單例模式，這裡就忽略記憶體釋放的問題了

class ConcreteStateA;

class ConcreteStateC:public State

{

public:

staticState* GetStateAInstance()

{

if(m_pInstance == NULL)

{

m_pInstance = new ConcreteStateC("狀態 C");

}

returnm_pInstance;

}

voidHandle(Context *pContext);

private:

ConcreteStateC(string name):State(name)

{ }

staticConcreteStateC *m_pInstance;

};

 

class ConcreteStateB:public State

{

public:

staticState* GetStateAInstance()

{

if(m_pInstance == NULL)

{

m_pInstance = new ConcreteStateB("狀態 B");

}

returnm_pInstance;

}

voidHandle(Context *pContext)

{

cout<<"狀態 B 處理的商務邏輯"<<endl;< p="">

ChangeState(pContext,ConcreteStateC::GetStateAInstance());

}

 

private:

ConcreteStateB(string name):State(name)

{ }

staticConcreteStateB *m_pInstance;

};

 

class ConcreteStateA:public State

{

public:

staticState* GetStateAInstance()

{

if(m_pInstance == NULL)

{

m_pInstance = new ConcreteStateA("狀態 A");

}

returnm_pInstance;

}

voidHandle(Context *pContext)

{

cout<<"狀態 A 處理的商務邏輯"<<endl;< p="">

ChangeState(pContext,ConcreteStateB::GetStateAInstance());

}

 

private:

ConcreteStateA(string name):State(name)

{ }

staticConcreteStateA *m_pInstance;

};

 

voidConcreteStateC::Handle(Context *pContext)

{

cout<<"狀態 C 處理的商務邏輯"<<endl;< p="">

ChangeState(pContext,ConcreteStateA::GetStateAInstance());

}

 

ConcreteStateA*ConcreteStateA::m_pInstance = NULL;

ConcreteStateB*ConcreteStateB::m_pInstance = NULL;

ConcreteStateC*ConcreteStateC::m_pInstance = NULL;

 

Context *pContext = new Context;

pContext->SetCurrentState(ConcreteStateA::GetStateAInstance());

pContext->Request();

pContext->Request();

pContext->Request();

狀態模式----C++實現