QTimer with QPaintEvent - c++

Question

I've created a small QT application that redraws a circle at a random position.
What I would like to do is repeat the method a predetermined number of times that draws the circle every second using a QTimer.
I am not sure how to go about to this.
Here is my main.cpp
int main(int argc, char *argv[]) {
// initialize resources, if needed
// Q_INIT_RESOURCE(resfile);
srand (time(NULL));
QApplication app(argc, argv);
widget f;
f.show();
return app.exec();
}
widget.cpp
#include "widget.h"
widget::widget()
{
widget.setupUi(this);
}
void widget::paintEvent(QPaintEvent * p)
{
QPainter painter(this);
//**code
printcircle(& painter); //paints the circle
//**code
}
void paintcircle(QPainter* painter)
{
srand (time(NULL));
int x = rand() %200 + 1;
int y = rand() %200 + 1;
QRectF myQRect(x,y,30,30);
painter->drawEllipse(myQRect);
}
widget::~widget()
{}
widget.h
#ifndef _WIDGET_H
#define _WIDGET_H
class widget : public QWidget {
Q_OBJECT
public:
widget();
virtual ~widget();
public slots:
void paintEvent(QPaintEvent * p);
private:
Ui::widget widget;
};
#endif /* _WIDGET_H */
How would I go about creating a Qtimer to repeat the printcricle() method.
Thanks

Answer 1

You can create a timer in your widget class constructor as:
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(update()));
timer->start(1000);
I.e. it will call the widget's paint event every second.

Answer 2

Right, there are a couple of things to modify in your code in order to accomplish this:
Forward declare a QTimer
Add a QTimer member
Include the QTimer header.
Set a continuous QTimer in the constructor of your widget class.
Make sure you set the connection to the update slot so that a repaint is scheduled by the event loop.
You need to add a counter for the predetermined times as there is no such feature built into QTimer.
You need to initialise that variable to zero.
You need to increment that in each slot call.
You need to stop emitting the timeout signal for the QTimer.
In order to achieve all that above, your code would become something like this:
widget.cpp
#include "widget.h"
#include <QTimer>
// Could be any number
const static int myPredeterminedTimes = 10;
widget::widget()
: m_timer(new QTimer(this))
, m_count(0)
{
widget.setupUi(this);
connect(m_timer, SIGNAL(timeout()), SLOT(update()));
timer->start(1000);
}
void widget::paintEvent(QPaintEvent * p)
{
QPainter painter(this);
//**code
printcircle(& painter); //paints the circle
//**code
}
void widget::paintcircle(QPainter* painter)
{
srand (time(NULL));
int x = rand() %200 + 1;
int y = rand() %200 + 1;
QRectF myQRect(x,y,30,30);
painter->drawEllipse(myQRect);
}
widget::~widget()
{}
widget.h
#ifndef _WIDGET_H
#define _WIDGET_H
class QTimer;
class widget : public QWidget {
Q_OBJECT
public:
widget();
virtual ~widget();
public slots:
void paintEvent(QPaintEvent * p);
private:
Ui::widget widget;
private:
QTimer *m_timer;
int m_count;
};
#endif /* _WIDGET_H */