Qt5 Tutorial QTimer - 2020

In this tutorial, we will learn about QTimer.

The QTimer class provides repetitive and single-shot timers.

The QTimer class provides a high-level programming interface for timers. To use it, create a QTimer, connect its timeout() signal to the appropriate slots, and call start(). From then on, it will emit the timeout() signal at constant intervals.

In this example, we'll use Qt Console application.

We need to create a MyTimer class:

Here are the codes:

mytimer.h:

#ifndef MYTIMER_H
#define MYTIMER_H

#include <QTimer>

class MyTimer : public QObject
{
    Q_OBJECT
public:
    MyTimer();
    QTimer *timer;

public slots:
    void MyTimerSlot();
};

#endif // MYTIMER_H

Note that MyTimer class is inherited from QObject. By inheriting from QObject, out class can use signal and slot mechanism Qt provides. Also, the macro Q_OBJECT set to make the MOC to function properly.

The MyTimerSlot() slot will be invoked when the timer signals timeout().

mytimer.cpp:

#include "mytimer.h"
#include <QDebug>

MyTimer::MyTimer()
{
    // create a timer
    timer = new QTimer(this);

    // setup signal and slot
    connect(timer, SIGNAL(timeout()),
          this, SLOT(MyTimerSlot()));

    // msec
    timer->start(1000);
}

void MyTimer::MyTimerSlot()
{
    qDebug() << "Timer...";
}

In the code, we creates QTimer object, and setup the signal and slot so that as soon as it the signal timeout() is emitted, our slot MyTimerSlot() prints out "Timer..." every seconds (1000ms).

void QTimer::start(int msec) starts or restarts the timer with a timeout interval of msec milliseconds. If the timer is already running, it will be stopped and restarted.

Finally, we need to make an instance of MyTimer class:

main.cpp:

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

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    
    // Create MyTimer instance
    // QTimer object will be created in the MyTimer constructor
    MyTimer timer;

    return a.exec();
}

If we run the code:

Timer...
Timer...
Timer...
Timer...
Timer...
...