设计模式读书笔记：State（状态）

意图&＃xff1a;

允许一个对象在其内部状态改变时改变它的行为。对象看起来似乎修改了它的类。

结构图&＃xff1a;来自 《23种设计模式 - 郗晓勇》

实现&＃xff1a;https://github.com/panshiqu/patterns/tree/master/State

Context

namespace NS_STATE {class State;
class Context {
public:Context(State *state) : _state(state) {}virtual ~Context() {}void request(void);private:friend class State;void changeState(State *state);private:State *_state;
};} /* namespace NS_STATE */

#include "Context.h"
#include "State.h"namespace NS_STATE {void Context::request(void)
{_state->handle(this);
}void Context::changeState(State *state)
{_state &＃61; state;
}} /* namespace NS_STATE */

State

#include "Context.h"namespace NS_STATE {class State {
public:State() {}virtual ~State() {}virtual void handle(Context *context) &＃61; 0;protected:void changeState(Context *context, State *state){context->changeState(state);}
};} /* namespace NS_STATE */

ConcreteStateA

#include "State.h"
#include "ConcreteStateB.h"
#include namespace NS_STATE {class ConcreteStateA : public State
{
public:ConcreteStateA() {}virtual ~ConcreteStateA() {}virtual void handle(Context *context){std::cout <<"ConcreteStateA." <};} /* namespace NS_STATE */ConcreteStateB

#include "State.h"
#include namespace NS_STATE {class ConcreteStateB : public State
{
public:ConcreteStateB() {}virtual ~ConcreteStateB() {}static ConcreteStateB *getInstance(void){static ConcreteStateB instance;return &instance;}virtual void handle(Context *context){std::cout <<"ConcreteStateB." <};} /* namespace NS_STATE */main

#include "State/Context.h"
#include "State/ConcreteStateA.h"
#include "State/ConcreteStateB.h"
using namespace NS_STATE;
int main(void)
{ConcreteStateA csa;Context c(&csa);c.request();c.request();
}附加&＃xff1a;