设计模式12：状态模式

系列总链接：《大话设计模式》学习记录_net 大话设计-CSDN博客

参考：设计模式之状态模式 (C++ 实现)_设计模式的状态模式实现-CSDN博客

1.概述

状态模式允许一个对象在其内部状态改变时改变其行为。对象看起来像是改变了其类。使用状态模式可以将状态的相关行为放在各个状态类中，从而实现状态切换的灵活性和可扩展性。

用例子来说明，小明是个大学生（对象），简化其状态为：困，饿，饱；简化行为：吃饭，睡觉，打王者；默认情况下小明的行为和状态之间的关系会有偶然性，所以会存在逻辑上的if-else组合，要考虑地全面，这分支无疑会比较多，并且可以出错。如果从状态模式处理小明状态和行为的逻辑问题，可以把小明的状态抽象为状态类(State)，各种具体的状态定为其的继承类(ConcreteState)，小明具体如何在行为和状态间切换的场景类(Context)。这样会比较清晰，各自的状态类下和其相关的行为会比较清晰；如果想新增状态类，也比较方便。

2.结构与实现

结构：

状态模式主要由以下几个部分构成：

Context (上下文)：持有一个具体的状态对象，并在状态之间切换。
State (状态接口)：定义一个接口用于在具体状态中实现不同的行为。
ConcreteState (具体状态)：实现状态接口的具体类，每个状态都有自己的行为。

实现：

参照概述的中例子，实现如下：

State.h:

#ifndef STATE_H
#define STATE_H

#include <QDebug>

class People;

class State
{
public:
    State() {}
    virtual void sleep(People* xiaoming)=0;
    virtual void eat(People* xiaoming)=0;
    virtual void playWangzhe(People* xiaoming)=0;
};

//疲劳
class tiredState : public State
{
public:
    tiredState(){}
    void sleep(People* people);
    void eat(People* people);
    void playWangzhe(People* people);
};

//饥饿
class hungryState : public State
{
public:
    hungryState(){}
    void sleep(People* people);
    void eat(People* people);
    void playWangzhe(People* people);
};

//饱
class fullState : public State
{
public:
    fullState(){}
    void sleep(People* people);
    void eat(People* people);
    void playWangzhe(People* people);
};

#endif // STATE_H

State.cpp:

#include "State.h"
#include "People.h"

void tiredState::sleep(People *people)
{
    qDebug() << "tired, go to sleeping and hungry.";
    people->setState(new hungryState());
}

void tiredState::eat(People *people)
{
    qDebug() << "tired, no want to eat...";
}

void tiredState::playWangzhe(People *people)
{
    qDebug() << "tired, no want to play...";
}

void hungryState::sleep(People *people)
{
    qDebug() << "hungry, no want to sleep...";
}

void hungryState::eat(People *people)
{
    qDebug() << "hungry, go to eat and full.";
    people->setState(new fullState());
}

void hungryState::playWangzhe(People *people)
{
    qDebug() << "hungry, no want to play...";
}

void fullState::sleep(People *people)
{
    qDebug() << "full, no want to sleep...";
}

void fullState::eat(People *people)
{
    qDebug() << "full, no want to eat...";
}

void fullState::playWangzhe(People *people)
{
    qDebug() << "full, go to play wangzhe and tired.";
    people->setState(new tiredState());
}

People.h:

#ifndef PEOPLE_H
#define PEOPLE_H

#include "State.h"

class People
{
public:
    People() {state = new tiredState();}
    ~People(){delete state;}

    void setState(State* newState){
        delete state;
        state = newState;
    }
    void play();
    void sleep();
    void eat();

private:
    State* state;
};
#endif // PEOPLE_H

People.cpp:

#include "People.h"
void People::play()
{
    state->playWangzhe(this);
}

void People::sleep()
{
    state->sleep(this);
}

void People::eat()
{
    state->eat(this);
}

main.cpp:

#include <QCoreApplication>
#include "People.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    People* xiaoming = new People();
    xiaoming->eat();
    xiaoming->play();
    xiaoming->sleep();
    xiaoming->eat();
    xiaoming->play();
    xiaoming->eat();

    delete xiaoming;
    return 0;
}

运行效果：

tired, no want to eat...
tired, no want to play...
tired, go to sleeping and hungry.
hungry, go to eat and full.
full, go to play wangzhe and tired.
tired, no want to eat...