What is the basic working of qtimer? - qt

Question

I created a rectangle and want it to move with QTimer , I want to know how the methods of QTimer exactly work. This code is running but the figure i drew is not moving.
.h
Header file
#ifndef WIDGET_H
#define WIDGET_H
#include <QWidget>
namespace Ui {
class Widget;
}
class Widget : public QWidget
{
Q_OBJECT
public:
explicit Widget(QWidget *parent = 0);
void paintEvent(QPaintEvent *event);
~Widget();
private slots:
void update();
private:
Ui::Widget *ui;
};
this is the .cpp file
.cpp
#include "widget.h"
#include "ui_widget.h"
#include<QPainter>
#include<QTimer>
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
QTimer *timer = new QTimer(this);
timer->setInterval(1000);
connect(timer, SIGNAL(timeout()), this, SLOT(update()));
timer->start();
}
Widget::~Widget()
{
delete ui;
}
void Widget::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.drawRect(50,80,70,80);
}
void Widget::update()
{
update();
}

Answer 1

You say "the figure i drew is not moving". In your code, I don't see code for a moving figure, I only see a static rectangle being drawn.
In addition, the update() function calls itself, leading to infinite recursion. Remove the update() from your code, the base class implementation QWidget::update() does the correct thing (scheduling a call to paintEvent()), no need to reimplement update().

Answer 2

First of all, update() slot method already has a specific meaning and purpose, you should not override it for other purposes. Further, it is not virtual, which tells you it is not even meant to be overriden (and doing it can lead to very confusing situations). So rename your own method to... updateAnimation() or something.
Then you need to add private member variables for your rectangle position, say rectX, rectY, rectWidth, rectHeight (or just single QRect if you prefer). Some code snippets help you get the idea:
void Widget::paintEvent(QPaintEvent *event)
{
// default setting is that Qt clears the widget before painting,
// so we don't need to worry about erasing previous rectangle,
// just paint the new one
QPainter painter(this);
painter.drawRect(rectX, rectY, rectWidth, rectHeight);
}
void Widget::updateAnimation()
{
// modify rectX, rectY, rectWidth and rectHeight here
update(); // make Qt do redrawing
}