QTimer with QPaintEvent

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 */