设计模式之抽象状态模式

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【定义】当一个对象的内在状态改变时，允许改变其行为，这个对象看起来像是改变了其类。

【场景】比如看一场电影，有以下状态买票状态：等待进场验票，进场状态：等待电影开始；看电影状态：等待电影结束；出场状态：等待下一场电影；

【UML】

【代码】

#include <iostream>using namespace std;class SeeFilm;class State{public:virtual void ChangeState(SeeFilm* seeFilm) = 0;virtual void ShowState() = 0;};class SeeFilm{private:State* state;public:void SetState(State* s){delete state;if(NULL != s){state = s;state->ShowState();}}void ChangeState(){state->ChangeState(this);}};class StateFilmOver : public State{public:virtual void ChangeState(SeeFilm* seeFilm){seeFilm->SetState(NULL);}virtual void ShowState(){cout<<"Current State: StateFilmOver"<<endl;}};class StateSeeFilm : public State{public:virtual void ChangeState(SeeFilm* seeFilm){seeFilm->SetState(new StateFilmOver());}virtual void ShowState(){cout<<"Current State: StateSeeFilm"<<endl;}};class StateWaitFilm : public State{public:virtual void ChangeState(SeeFilm* seeFilm){seeFilm->SetState(new StateSeeFilm());}virtual void ShowState(){cout<<"Current State: StateWaitFilm"<<endl;}};class StateGetTicket : public State{public:virtual void ChangeState(SeeFilm* seeFilm){seeFilm->SetState(new StateWaitFilm());}virtual void ShowState(){cout<<"Current State: StateGetTicket"<<endl;}};int main(){SeeFilm* seeFilm = new SeeFilm();State* state = new StateGetTicket();seeFilm->SetState(state);seeFilm->ChangeState();seeFilm->ChangeState();seeFilm->ChangeState();delete seeFilm;return 0;}