通用Gate方式的FSM接口，

//-------------------------------------------
#include "IGateState.h"
#include <assert.h>
#include <iostream.h>
//-------------------------------------------

//-------------------------------------------
class IGateFSM
{
public:
IGateFSM();
virtual ~IGateFSM();

public:

inline void SetState(IGateState * state) {_state = state;}

virtual void OnEvent(ENUM_EVENT event);

private:
IGateState * _state;
};
//-------------------------------------------

// 派生类的实现，以地铁十字专门为模型，提供Lock/UnLock等与业务相关的方法

//-------------------------------------------

class VGateFSM : public IGateFSM
{
public:
VGateFSM() {}
virtual ~VGateFSM() {}

public:

void Lock();
void UnLock();
void Alarm();
void Thanks();

private:
bool m_IsLock;

};
//-------------------------------------------

//================================
// ′代表状态类的抽象接口
class IGateFSM;

// 事件描述
enum ENUM_EVENT
{
EVENT_COIN, // í?è?ó2±òê??t
EVENT_PASS // ′???ê??t
};

class IGateState
{
public:
IGateState();
virtual ~IGateState();

public:

virtual void OnEvent(ENUM_EVENT event, IGateFSM * fsm) = 0;

};
//------------------------------------------

// State模式的实现类，代表两种状态

class VGateLock : public IGateState
{
public:
static IGateState * Instance();

public:
virtual void OnEvent(ENUM_EVENT event, IGateFSM * fsm);

private:
VGateLock(){}

static VGateLock * _instance;

};
//------------------------------------------
class VGateUnLock : public IGateState
{
public:
static IGateState * Instance();

public:
virtual void OnEvent(ENUM_EVENT event, IGateFSM * fsm);

private:
VGateUnLock(){}

static VGateUnLock * _instance;

};

// FSM的实现

//-------------------------------------------
IGateFSM::IGateFSM()
{
_state = NULL;
}
IGateFSM::~IGateFSM()
{
}
//-------------------------------------------
void IGateFSM::OnEvent(ENUM_EVENT event)
{
assert(_state != NULL);

_state->OnEvent(event,this);
}
//-------------------------------------------
void VGateFSM::Lock()
{
this->m_IsLock = true;

cout<<"Lock the gate."<<endl;
}
//-------------------------------------------
void VGateFSM::UnLock()
{
this->m_IsLock = true;

cout<<"Unlock the gate."<<endl;
}
//-------------------------------------------
void VGateFSM::Alarm()
{
cout<<"You should insert a coin."<<endl;
}
//-------------------------------------------
void VGateFSM::Thanks()
{
cout<<"Thank You for pay again."<<endl;
}
//-------------------------------------------

// state的实现部分

VGateLock * VGateLock::_instance = NULL;
VGateUnLock * VGateUnLock::_instance = NULL;
void VGateLock::OnEvent(ENUM_EVENT event, IGateFSM * fsm)
{
VGateFSM * vfsm = (VGateFSM *) fsm;

if (event == EVENT_PASS)
{
vfsm->Alarm();
return ;
}

if (event == EVENT_COIN)
vfsm->UnLock();

vfsm->SetState(VGateUnLock::Instance());

}
//-------------------------------------------
void VGateUnLock::OnEvent(ENUM_EVENT event, IGateFSM * fsm)
{
VGateFSM * vfsm = (VGateFSM *) fsm;

if (event == EVENT_COIN)
{
vfsm->Thanks();
return ;
}

if (event == EVENT_PASS)
vfsm->Lock();

vfsm->SetState(VGateLock::Instance());
}
//-------------------------------------------
IGateState * VGateLock::Instance()
{
if (_instance == NULL)
_instance = new VGateLock();

return _instance;
}
//-------------------------------------------
IGateState * VGateUnLock::Instance()
{
if (_instance == NULL)
_instance = new VGateUnLock();

return _instance;
}
//-------------------------------------------

测试程序：

int main(int argc, char* argv[])
{
printf("FSM Demo:\n\n");

VGateFSM * _fsm = new VGateFSM();

_fsm->SetState(VGateLock::Instance());

_fsm->OnEvent(EVENT_PASS);
_fsm->OnEvent(EVENT_COIN);
_fsm->OnEvent(EVENT_COIN);
_fsm->OnEvent(EVENT_PASS);

delete _fsm;

printf("\n");
return 0;
}

可以看到输出为：

You should insert a coin.

Unlock the gate

Thank You for pay again.

Lock the gate.

与预期结果一样

小结：

有限状态机是OO中的一种建模方法，是以状态对象角度来分析解决问题，最主要的是通过建立抽象的状态类，以及相关的实现类，把状态的处

理，转换在派生类中实现，从而实现比较良好的逻辑与实现分开。

另：结构上与Strategy,Observer都类似，看来模式也不用记得那么死，其实都有相通的地方。。

UML图片咋粘贴不上来？怪。