简单有限状态机(FSM)的实现

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,  // ͶÈëÓ²±Òʼþ
 EVENT_PASS  // ´©Ô½Ê¼þ
};
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。