Qt C++ State模式

最新推荐文章于 2024-07-12 15:00:22 发布

原创最新推荐文章于 2024-07-12 15:00:22 发布 · 777 阅读

0 ·

CC 4.0 BY-SA版权

C++设计模式专栏收录该内容

26 篇文章

订阅专栏

本文通过一个具体实例介绍了状态模式(State Pattern)的基本概念及其在C++中的实现方式。该模式允许对象在其内部状态改变时改变它的行为，使得看似复杂的行为能够对应于一系列的状态对象。

我们在做多个条件判断的时候常会用到switch,如果条件和内容过于繁琐，内容庞大的话，state模式就十分有用了。

state.h

#pragma once

#include <QDebug>

class CState;
class CContext
{
public:
CContext(CState* state):m_state(state){}
~CContext();
void request();
void changeState(CState* state);

private:
CState* m_state;
};

class CState
{
public:
virtual void Handle(CContext *context) = 0;
};

class CConcreateStateA : public CState
{
public:
CConcreateStateA(){qDebug() << "this stateA!";}

public:
void Handle(CContext *context);
};

class CConcreateStateB : public CState
{
public:
CConcreateStateB(){qDebug() << "this stateB!";}

public:
void Handle(CContext *context);
};

state.cpp

#include "state.h"

CContext::~CContext()
{
delete m_state;
}

void CContext::request()
{
if (m_state)
{
m_state->Handle(this);
}
}

void CContext::changeState(CState* state)
{
if (m_state)
{
delete m_state;
m_state = 0;
}
m_state = state;
}

void CConcreateStateA::Handle(CContext *context)
{
if (context)
{
context->changeState(new CConcreateStateB);
}
}

void CConcreateStateB::Handle(CContext *context)
{
if (context)
{
context->changeState(new CConcreateStateA);
}
}

main.cpp

#include <QApplication>
#include "state.h"

int main(int argc,char **argv)
{
QApplication app(argc,argv);
CConcreateStateA *stateA = new CConcreateStateA;
CContext *context = new CContext(stateA);
context->request();
context->request();
context->request();
delete context;

return app.exec();
}