paintEvent not getting called with QMainWindow

[DiamonDogX]

I have a class that extends QMainWindow and I overrode the paintEvent method, but it never gets called. I have done something similar when extending QWidget and it does call the method. A little confused here... it seems to be declared correctly:

protected:
virtual void paintEvent(QPaintEvent*);
....
....
void MyWindow:: paintEvent(QPaintEvent*)
{
// never gets here
}

[caduel]

show us more code, please.

[DiamonDogX]

class MyWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow();
virtual ~MainWindow();

protected:
virtual void paintEvent(QPaintEvent*);
....
....
};

// Class implementation:
void MyWindow:: paintEvent(QPaintEvent*)
{
// Never gets called
}

[sorin]

Remove virtual from paintEvent definition and retry

[wysota]

How do you know it never gets called?

[spirit]

Remove virtual from paintEvent definition and retry

why? do you think it solves the problem? it's not mistake.

[spirit]

I think he is trying to draw something and he expects that the image should appear on central widget. it's just a guess. :) if I'm right, then you need:
* install event filter on central widget,
* subclass a QWidget, override paintEvent and then set this widget as central widget on 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);
}

[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();
}

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);
}