详解state状态模式及在C++设计模式编程中的使用实例

//state.h
#ifndef _STATE_H_
#define _STATE_H_
class Context; //前置声明
class State{
  public:
  State();
  virtual ~State();
  virtual void OperationInterface(Context* ) = 0;
  virtual void OperationChangeState(Context*) = 0;
  protected:
  bool ChangeState(Context* con,State* st);
  private:
  //bool ChangeState(Context* con,State* st);
};
class ConcreteStateA:public State{
  public:
  ConcreteStateA();
  virtual ~ConcreteStateA();
  virtual void OperationInterface(Context* );
  virtual void OperationChangeState(Context*);
  protected:
  private:
};
class ConcreteStateB:public State{
  public:
  ConcreteStateB();
  virtual ~ConcreteStateB();
  virtual void OperationInterface(Context* );
  virtual void OperationChangeState(Context*);
  protected:
  private:
};
#endif //~_STATE_H_

//State.cpp
#include "State.h"
#include "Context.h"
#include <iostream>
using namespace std;
State::State(){
}
State::~State(){
}
void State::OperationInterface(Context* con){
  cout<<"State::.."<<endl;
}
bool State::ChangeState(Context* con,State* st){
  con->ChangeState(st);
  return true;
}
void State::OperationChangeState(Context* con){
}
///
ConcreteStateA::ConcreteStateA(){
}
ConcreteStateA::~ConcreteStateA(){
}
void ConcreteStateA::OperationInterface(Context* con){
  cout<<"ConcreteStateA::OperationInterface
  ......"<<endl;
}
void ConcreteStateA::OperationChangeState(Context* con){
  OperationInterface(con);
  this->ChangeState(con,new ConcreteStateB());
}
///
ConcreteStateB::ConcreteStateB(){
}
ConcreteStateB::~ConcreteStateB(){
}
void ConcreteStateB::OperationInterface(Context* con){
  cout<<"ConcreteStateB::OperationInterface......"<<endl;
}
void ConcreteStateB::OperationChangeState(Context* con){
  OperationInterface(con);
  this->ChangeState(con,new ConcreteStateA());
}

//context.h
#ifndef _CONTEXT_H_
#define _CONTEXT_H_
class State;
/**
*
**/
class Context{
  public:
  Context();
  Context(State* state);
  ~Context();
  void OprationInterface();
  void OperationChangState();
  protected:
  private:
  friend class State; //表明在 State 类中可以访问 Context 类的 private 字段
  bool ChangeState(State* state);
  private:
  State* _state;
};
#endif //~_CONTEXT_H_

//context.cpp
#include "Context.h"
#include "State.h"
Context::Context(){
}
Context::Context(State* state){
  this->_state = state;
}
Context::~Context(){
  delete _state;
}
void Context::OprationInterface(){
  _state->OperationInterface(this);
}
bool Context::ChangeState(State* state){
  ///_state->ChangeState(this,state);
  this->_state = state;
  return true;
}
void Context::OperationChangState(){
  _state->OperationChangeState(this);
}

//main.cpp
#include "Context.h"
#include "State.h"
#include <iostream>
using namespace std;
int main(int argc,char* argv[]){
  State* st = new ConcreteStateA();
  Context* con = new Context(st);
  con->OperationChangState();
  con->OperationChangState();
  con->OperationChangState();
  if (con != NULL)
    delete con;
  if (st != NULL)
    st = NULL;
  return 0;
}