paintEvent not getting called with QMainWindow

[DiamonDogX]

Yes, spirit, you're pretty much right. Being relatively new to Qt, I am discovering its quirks. I guess by design the paintEvent will not get called in my case of the QMainWindow. I understand that my event filter should capture events from the central widget, but what type of code would I need in my eventFilter() method to ensure this works, i.e. gets painted?

[spirit]

you should do like this

bool MyMainWindow::eventFilter(QObject *o, QEvent *e)
{
    if (o == centralWidget() && e->type() == QEvent::Paint) {
        //paint on central widget
        ...
    }
    return QMainWindow::eventFilter(o, e);
}

bool MyMainWindow::eventFilter(QObject *o, QEvent *e)
{
    if (o == centralWidget() && e->type() == QEvent::Paint) {
        //paint on central widget
        ...
    }
    return QMainWindow::eventFilter(o, e);
}

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[wysota]

I guess by design the paintEvent will not get called in my case of the QMainWindow.

It is called. You just don't see its result because something else paints over it.

[yodasoda]

How can you say its called or not. I am in the same situation and I simply put a breakpoint in the function and the program never reached the breakpoint therefor it is not getting called.

[wysota]

You just check if it is called:

#include <QtGui>
 
class MyWindow : public QMainWindow {
public:
  MyWindow(){}
protected:
  void paintEvent(QPaintEvent *pe){
    qDebug() << Q_FUNC_INFO;
    QMainWindow::paintEvent(pe);
  }
};
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  MyWindow mw;
  mw.show();  
  return app.exec();
}

#include <QtGui>

class MyWindow : public QMainWindow {
public:
  MyWindow(){}
protected:
  void paintEvent(QPaintEvent *pe){
    qDebug() << Q_FUNC_INFO;
    QMainWindow::paintEvent(pe);
  }
};

int main(int argc, char **argv){
  QApplication app(argc, argv);
  MyWindow mw;
  mw.show();  
  return app.exec();
}

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In this example it is called.

[yodasoda]

In my case, this was happening with a QFrame. Here is the solution if anyone ever needs it:

rgbFrame::rgbFrame(QWidget * parent, Qt::WindowFlags f): QFrame(parent, f)
{
    installEventFilter(this);
}
 
void rgbFrame::paintEvent(QPaintEvent *e)
{
    QFrame::paintEvent(e); // pass event to base class
}
 
 
bool rgbFrame::eventFilter(QObject *o, QEvent *e)
{
    if (e->type() == QEvent::Paint) {
        paintEvent((QPaintEvent *)e);
    }
    return QFrame::eventFilter(o, e);
}

rgbFrame::rgbFrame(QWidget * parent, Qt::WindowFlags f): QFrame(parent, f)
{
    installEventFilter(this);
}

void rgbFrame::paintEvent(QPaintEvent *e)
{
    QFrame::paintEvent(e); // pass event to base class
}


bool rgbFrame::eventFilter(QObject *o, QEvent *e)
{
    if (e->type() == QEvent::Paint) {
        paintEvent((QPaintEvent *)e);
    }
    return QFrame::eventFilter(o, e);
}

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