can't new qwebview in a mainwindow constructor

[calhal]

Qwidget: must construct a QApplication before a QPaintDevice

Your answer is here. You have to construct QApplication first.
Normally your main.cpp should look somehow like that:

#include <QtGui/QApplication>
 
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

#include <QtGui/QApplication>

#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

To copy to clipboard, switch view to plain text mode 

You can try to use QtCreator to start a new project - this code will be generated automatically.

Next time in your posts please use correct tags (quote, code etc.) and write in a proper forum (this post should be in newbie forum).