timer->start(100);

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QTimer>

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT

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

private slots:
    void on_btnStart_clicked();

    void on_btnStop_clicked();

    void on_Timer_Timeout();
private:
    Ui::Dialog *ui;
    QTimer *timer;
};

#endif // DIALOG_H

#include "dialog.h"
#include "ui_dialog.h"

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    timer=new QTimer();
    QObject::connect(timer,SIGNAL(timeout()),this,SLOT(on_Timer_Timeout()));
}

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

void Dialog::on_Timer_Timeout()
{
    int v=ui->progressBar->value();
    if(v>=100)
    {
        v=0;
        ui->progressBar->setValue(v);
    }else{
        ui->progressBar->setValue(v+1);
    }

}

void Dialog::on_btnStart_clicked()
{
    timer->start(100);
}

void Dialog::on_btnStop_clicked()
{
    timer->stop();

}