1. 概述

在QT中使用定时器QTimer时，一不小心可能就会造成定时器失效的情况，这个问题的本质是QTimer实例运行在了一个没有启用事件循环的线程中，从而造成其失效

2. 使用场景

主线程中使用
子线程中使用

2.1 注意

定时器的创建与使用要在同一个线程中，这个问题的演示会在2.2.2 QThread小节中进行

2.2 主线程中使用

首先创建一个QTimerInMainThread类，内容如下：

#ifndef QTIMERRUNINTHREAD_H
#define QTIMERRUNINTHREAD_H#include <QObject>
#include <QTimer>class QTimerInMainThread : public QObject
{Q_OBJECT
public:QTimerInMainThread();~QTimerInMainThread();QTimer m_timer;int m_count;
public slots:void timeoutHandle();};#endif // QTIMERRUNINTHREAD_H

实现QTimerInMainThread类

#include "QTimerRunInThread.h"
#include <QThread>
#include <QDebug>QTimerInMainThread::QTimerInMainThread(): m_count(0)
{QObject::connect(&m_timer,&QTimer::timeout,this,&QTimerInMainThread::timeoutHandle);m_timer.start(100);
}QTimerInMainThread::~QTimerInMainThread()
{m_timer.stop();
}void QTimerInMainThread::timeoutHandle()
{qDebug() << "current thread id: " <<  QThread::currentThreadId() << "m_count: " << m_count++;
}

main.cpp

#include <QCoreApplication>
#include "QTimerObjectInQThread.h"
#include <QDebug>
#include <QThread>int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);qDebug() << "main thread id: " <<  QThread::currentThreadId() ;/** 第一种方式：定时器运行在主线程中*  直接主线程中启动一个定时器*/static QTimerInMainThread mainThreadTimer;return a.exec();
}

2.3 子线程中使用

在QT中线程的使用通常分为两种，接下来就以这两种进行举例。

2.3.1 moveToThread

创建QTimerMoveToChildrenThread类

#ifndef QTIMERMOVETOCHILDRENTHREAD_H
#define QTIMERMOVETOCHILDRENTHREAD_H#include <QObject>
#include <QTimer>
#include <QThread>class QTimerMoveToChildrenThread: public QObject
{Q_OBJECT
public:QTimerMoveToChildrenThread();~QTimerMoveToChildrenThread();void start();void stop();QTimer m_timer;QThread m_timerThread;int m_count;signals:void startSignal(int msec);void stopSignal();public slots:void timeoutHandle();
};#endif // QTIMERMOVETOCHILDRENTHREAD_H

实现QTimerMoveToChildrenThread类

#include "QTimerMoveToChildrenThread.h"
#include <QDebug>QTimerMoveToChildrenThread::QTimerMoveToChildrenThread(): m_count(0)
{// 更改定时器运行的线程m_timer.moveToThread(&m_timerThread);// 定时器触发事件connect(&m_timer,&QTimer::timeout,this,&QTimerMoveToChildrenThread::timeoutHandle);// 连接定时器启动槽函数QObject::connect(this,static_cast<void (QTimerMoveToChildrenThread::*)(int)>(&QTimerMoveToChildrenThread::startSignal),&m_timer,static_cast<void (QTimer::*)(int)>(&QTimer::start));// 连接定时器关闭槽函数QObject::connect(this,&QTimerMoveToChildrenThread::stopSignal,&m_timer,&QTimer::stop);m_timerThread.start();
}QTimerMoveToChildrenThread::~QTimerMoveToChildrenThread()
{stop();m_timerThread.quit();
}void QTimerMoveToChildrenThread::start()
{//向子线程内的定时器发送开启定时器信号emit startSignal(100);
}void QTimerMoveToChildrenThread::stop()
{//向子线程内的定时器发送停止定时器信号emit stopSignal();
}void QTimerMoveToChildrenThread::timeoutHandle()
{// 这个在主线程中执行qDebug() << "current thread id: " <<  QThread::currentThreadId() << "m_count: " << m_count++;
}

main.cpp

#include <QCoreApplication>
#include "QTimerMoveToChildrenThread.h"
#include <QDebug>
#include <QThread>int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);qDebug() << "main thread id: " <<  QThread::currentThreadId() ;/** 第二种方式：定时器运行在子线程中*  将定时器移动到子线程中，外部发送启动信号启动子线程中的定时器*/static QTimerMoveToChildrenThread moveToChildrenThreadTimer;moveToChildrenThreadTimer.start();return a.exec();
}

2.3.2 QThread

创建QTimerObjectInQThread类

#ifndef QTIMEROBJECTINQTHREAD_H
#define QTIMEROBJECTINQTHREAD_H#include <QObject>
#include <QThread>
#include <QTimer>class QTimerObjectInQThread : public QThread
{Q_OBJECT
public:QTimerObjectInQThread();~QTimerObjectInQThread();QTimer* m_ptimer;int m_count;public slots:void timeoutHandle();protected:virtual void run() override;
};#endif // QTIMEROBJECTINQTHREAD_H

实现QTimerObjectInQThread类

#include "QTimerObjectInQThread.h"
#include <QDebug>QTimerObjectInQThread::QTimerObjectInQThread(): m_count(0)
{}QTimerObjectInQThread::~QTimerObjectInQThread()
{if(m_ptimer){m_ptimer->stop();delete m_ptimer;}
}void QTimerObjectInQThread::timeoutHandle()
{qDebug() << "current thread id: " <<  QThread::currentThreadId() << "m_count: " << m_count++;
}void QTimerObjectInQThread::run()
{m_ptimer = new QTimer;connect(m_ptimer,&QTimer::timeout,this,&QTimerObjectInQThread::timeoutHandle);m_ptimer->start(100);// 启动事件循环，否则定时器无法生效exec();
}

main.cpp

#include <QCoreApplication>
#include "QTimerRunInThread.h"
#include "QTimerMoveToChildrenThread.h"
#include "QTimerObjectInQThread.h"
#include <QDebug>
#include <QThread>int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);qDebug() << "main thread id: " <<  QThread::currentThreadId() ;/** 第二种方式：定时器运行在子线程中*  在线程的run()中启动定时器*/QTimerObjectInQThread timerObjectInThread;timerObjectInThread.start();return a.exec();
}

2.3.2.1 定时器不能在另一个线程启动问题演示

将QTimer* m_ptimer;修改为QTimer m_ptimer;

QTimerObjectInQThread类的实现修改如下

#include "QTimerObjectInQThread.h"
#include <QDebug>QTimerObjectInQThread::QTimerObjectInQThread(): m_count(0)
{}QTimerObjectInQThread::~QTimerObjectInQThread()
{//    if(m_ptimer)
//    {//        m_ptimer->stop();
//        delete m_ptimer;
//    }
}void QTimerObjectInQThread::timeoutHandle()
{qDebug() << "current thread id: " <<  QThread::currentThreadId() << "m_count: " << m_count++;
}void QTimerObjectInQThread::run()
{//m_ptimer = new QTimer;connect(&m_ptimer,&QTimer::timeout,this,&QTimerObjectInQThread::timeoutHandle);m_ptimer.start(100);// 启动事件循环，否则定时器无法生效exec();
}

运行项目会输出以下内容
QObject::startTimer: Timers cannot be started from another thread

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