QWebPage / QPrinter - can't load page

I am new in Qt and I need to do a program who export html page to PDF

So, the main idea is use QWebPage for interpret html and export itself to pdf with QPrinter.

I have two class webview who use QWebPage and Print who use QPrinter.

In main.cpp I have connect LoadFinished to PrintPDF slot:

Print *pdf = new Print(args);
webview *nav = new webview();
nav->setPrinter(pdf->getPrinter());

if(nav->load(args) == false) {
    qDebug() << "can't load page";
    return 0;
}
//when the page page is ready, we will print it
QObject::connect(nav->getFrame(), SIGNAL(loadFinished(bool)), nav, SLOT(printPDF(bool)));

My webview.cpp class:

#include "webview.h"
webview::webview()
{
    page = new QWebPage;
    printer = 0;
}

webview::~webview()
{
    delete page;
}

bool webview::load(Arguments *args)
{
    QRegularExpression url("^(file|http)://");
    QRegularExpression fullPath("^/");

    QRegularExpressionMatch pathMatch = fullPath.match(args->getSource());
    QRegularExpressionMatch urlMatch = url.match(args->getSource());

    // see http://qt-project.org/doc/qt-4.8/qwebsettings.html#WebAttribute-enum for more informations
    page->settings()->setAttribute(QWebSettings::LocalStorageEnabled, true);
    page->settings()->setAttribute(QWebSettings::AutoLoadImages, true);
    page->settings()->setAttribute(QWebSettings::JavascriptEnabled, true);
    page->settings()->setAttribute(QWebSettings::PrintElementBackgrounds, true);
    page->settings()->setAttribute(QWebSettings::PluginsEnabled, true);

    if(pathMatch.hasMatch()) {
        page->mainFrame()->load(QUrl::fromLocalFile(args->getSource()));
    } else {
        if (urlMatch.hasMatch()) {
            page->mainFrame()->load(QUrl(args->getSource()));
        } else {
            fprintf(stderr, "%s\n", qPrintable(QApplication::translate("main", "Error: Invalide source file")));
            return false;
        }
    }
    return true;
}

void webview::printPDF(bool ok)
{
    if(ok == true) {
        qDebug() << "okay";
    } else
        qDebug() << "non okay";
    if(printer != 0)
        page->mainFrame()->print(printer);
}

This is what my console display:

non okay
QPainter::begin: A paint device can only be painted by one painter at a time.

I have no idea where the error might be due. The whole project is here

The arguments are:

./htmltopdf http://stackoverflow.com destinationFolder

(destinationFolder is not yet implemented, you must directly modify the source code)

The problem was elsewhere :

In my main.cpp I had this :

QObject::connect(nav->getFrame(), SIGNAL(loadFinished(bool)), nav, SLOT(printPDF(bool)));
[...]
delete args;
delete pdf;
delete nav;

return app.exec();

app.exec() is a kind of infinit loop who thaht handles Qt events and thus allows the program does not close. If I proceed to delete before calling this function,then I will have freshly deallocated pointers that will be used

If I Do :

bool result = app.exec();

delete args;
delete pdf;
delete nav;

return result;

It's work fine !