Two methods of QT to realize timer

Method 1

1、 Rewrite the virtual function

void timerEvent(QTimerEvent* e);

2、 Start timer

• Return value is timer id, The parameter is timing interval , The unit is millisecond

int startTimer(int interval)

Code

• widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTimerEvent>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
protected:
    void timerEvent(QTimerEvent *e);

private slots:
    void on_pushButton_clicked();
    void on_pushButton_close_clicked();

private:
    Ui::Widget *ui;
    int timerId;
};

#endif // WIDGET_H

• widget.cpp

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
}

Widget::~Widget()
{
    delete ui;
}

//  Timed interval to , The function will be called automatically 
void Widget::timerEvent(QTimerEvent *e)
{
	// Conduct relevant business 
    if(e->timerId() == timerId){
        static int i = 0;
        ui->lineEdit->setText(QString("timer: %1").arg(i++));
    }
}

void Widget::on_pushButton_clicked()
{
    //  Start timer . Parameters ： Timing time (ms)
    timerId = startTimer(1000);
}

void Widget::on_pushButton_close_clicked()
{
    killTimer(timerId);
}

Method 2

1、 Define a QTimer object

QTimer* timer;

2、 Start timer

• The parameter is timing interval , The unit is millisecond

void QTimer::start(std::chrono::milliseconds msec)

3、 Connect the signal slot

• Timed interval to ,QTimer Object emits a timeout The signal . Connect the signal slot , Perform relevant operations in the slot function

[signal] void QTimer::timeout()

Code

• widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTimer>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private slots:
    void on_pushButton_clicked();

    void on_pushButton_close_clicked();

    void timeoutSlot();
private:
    Ui::Widget *ui;
    QTimer* timer;
};

#endif // WIDGET_H

• widget.cpp

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    timer = new QTimer(this);

    // Connect the signal slot 
    connect(timer, &QTimer::timeout, this, &Widget::timeoutSlot);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::on_pushButton_clicked()
{
    // Start timer 
    timer->start(1000);
}

void Widget::on_pushButton_close_clicked()
{
    // off timer 
    timer->stop();
}

void Widget::timeoutSlot()
{
    // Conduct relevant business 
    static int i = 0;
    ui->lineEdit->setText(QString("timer: %1").arg(i++);
}

effect