QProgressbar not updating

Xena_o

Hello

i am trying to use a progress bar but it is not updating when i set new value to it.
So far i read few thread and posts here and there, speaking about using threads etc. i tried bunch of things, nothing working except some examples showing a slider being connected to a progress bar, but it is not what i want.

here is my test code:

#include "mainwindow.h"
#include "ui_mainwindow.h"


#include <QObject>

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


connect(this, SIGNAL(updatePB()), this, SLOT(changeProgressBarValue()));

        ui->progressBar->setValue(0);
}

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

void MainWindow::changeProgressBarValue()
{
    test=test + 3;

    int b = (test / 60) * 100;
    ui->progressBar->setValue(b);

   // ui->horizontalSlider->setValue(b);
    //QCoreApplication::processEvents();
    //qApp->processEvents();

}
void MainWindow::on_pushButton_clicked()
{
    emit updatePB();
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

    int test=0;

signals:
    void updatePB();

private slots:
    void on_pushButton_clicked();

    void changeProgressBarValue();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

in this example the progress bar should change when i click a button, but it is not changing, it only changes when i click the button 20 times, because the value reaches 100%

Also this example is based on some recommandations i read but in my case i want the progress bar to update immediatly when i change its value (i dont want to use a thread or a signal/slot), i have tried to call processEvents() but this did not work too...

Any idea to get the progress bar works ?
thanks

nagesh

@Xena_o looks like integer division is happening here

int b = (test / 60) * 100;

change it to 60.0 it will work
int b = (test / 60.0) * 100;

Xena_o

@nagesh ugh! i wasted so much time because of a .0 !!!
thank you !

jeremy_k

Performing the multiplication first avoids the need to convert to floating point to reduce precision loss. It is also likely faster.

int b = (test * 100) / 60;

JonB

@Xena_o
I agree with @jeremy_k. No point doing floating point anything when integer division will do! I would suggest a slight amendment:

int b = (test * 100 + 30) / 60;

rounds to nearest instead of flooring :)

Solved QProgressbar not updating