解析C++编程中如何使用设计模式中的状态模式结构

#define _STATE_H_

class Context;
class State
{
public:
  virtual void Handle(Context* pContext)=0;
  ~State();
protected:
  State();
private:
};

class ConcreteStateA : public State
{
public:
  ConcreteStateA();
  ~ConcreteStateA();
  virtual void Handle(Context* pContext);
protected:
private:
};

class ConcreteStateB : public State
{
public:
  ConcreteStateB();
  ~ConcreteStateB();
  virtual void Handle(Context* pContext);
protected:
private:
};

class ConcreteStateC : public State
{
public:
  ConcreteStateC();
  ~ConcreteStateC();
  virtual void Handle(Context* pContext);
protected:
private:
};

class Context
{
public:
  Context(State* pState);
  ~Context();
  void Request();
  void ChangeState(State* pState);
protected:
private:
  State* _state;
};


#endif

#include "State.h"
#include <iostream>

using namespace std;

State::State()
{}

State::~State()
{}

ConcreteStateA::ConcreteStateA()
{}

ConcreteStateA::~ConcreteStateA()
{}

//执行该状态的行为并改变状态
void ConcreteStateA::Handle(Context* pContext)
{
  cout << "ConcreteStateA" << endl;
  pContext->ChangeState(new ConcreteStateB());
}

ConcreteStateB::ConcreteStateB()
{}

ConcreteStateB::~ConcreteStateB()
{}

//执行该状态的行为并改变状态
void ConcreteStateB::Handle(Context* pContext)
{
  cout << "ConcreteStateB" << endl;
  pContext->ChangeState(new ConcreteStateC());
}

ConcreteStateC::ConcreteStateC()
{}

ConcreteStateC::~ConcreteStateC()
{}

//执行该状态的行为并改变状态
void ConcreteStateC::Handle(Context* pContext)
{
  cout << "ConcreteStateC" << endl;
  pContext->ChangeState(new ConcreteStateA());
}

//定义_state的初始状态
Context::Context(State* pState)
{
  this->_state = pState;
}

Context::~Context()
{}

//对请求做处理，并设置下一状态
void Context::Request()
{
  if(NULL != this->_state)
  {
    this->_state->Handle(this);
  }
}

//改变状态
void Context::ChangeState(State* pState)
{
  this->_state = pState;
}

int main()
{
  State* pState = new ConcreteStateA();
  Context* pContext = new Context(pState);
  pContext->Request();
  pContext->Request();
  pContext->Request();
  pContext->Request();
  pContext->Request();
  return 0;
}