State模式-白红宇

State模式

阅读量：4133 次

发布时间：2019-05-25

本文共 2412 字，大约阅读时间需要 8 分钟。

State模式将状态逻辑和动作实现进行分离。当一个操作中要维护大量的case分支语句，并且这些分支依赖于对象的状态。State模式将每个分支都封装到独立的类中。

State.h

//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

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

Context.h

//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

//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){	this->_state= state;	return true;}void Context::OperationChangState(){	_state->OperationChangeState(this);}

State模式和Strategy模式有很大程度上的相似，实际上State模式和Strategy模式所关注的点不尽相同：State模式主要是适应对象对于状态改变时的不同处理策略的实现，而Strategy模式主要是具体算法和实现接口的解耦。

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