PyQt application crashes after closing QMessagebox window.

Question

Here is the code of my simple tray application. It crashes with segfault when i call information window from context menu of application and then close it. I've tryed different variants to find a reason of segfault, this is my last try.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtCore
from PyQt4 import QtGui    

class SystemTrayIcon(QtGui.QSystemTrayIcon):
    def __init__(self, parent=None):
        QtGui.QSystemTrayIcon.__init__(self, parent)

        self.setIcon(QtGui.QIcon("icon.png"))

        self.iconMenu = QtGui.QMenu(parent)
        appabout = self.iconMenu.addAction("About")
        appexit = self.iconMenu.addAction("Exit")
        self.setContextMenu(self.iconMenu)

        self.aboutdialog = QtGui.QWidget(parent)

        self.connect(appabout,QtCore.SIGNAL('triggered()'),self.showAbout)
        self.connect(appexit,QtCore.SIGNAL('triggered()'),self.appExit)

        self.show()


    def showAbout(self):
        QtGui.QMessageBox.information(self.aboutdialog, self.tr("About Tunarium"), self.tr("Your text here."))

    def appExit(self):
        sys.exit()


if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)

    trayIcon = SystemTrayIcon()
    trayIcon.show()

    sys.exit(app.exec_())

Answer 1

I don't know Python but in your appExit(), you should be calling quit() or exit() on the application object which will cause your call to sys.exit(app.exec_()) in main to return. Again, not knowing the Python specifics, you can do this by using the Qt macro qApp and call qApp->quit() or QCoreApplication::instance()->quit().

Calling quit() is the same as calling exit(0). You can use exit() directly to return any exit code of your choice.

Update: I've tried your code in C++ with a few tweaks and it does work. I've commented where you should try making changes to your code. Hope it works for you.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtCore
from PyQt4 import QtGui    

class SystemTrayIcon(QtGui.QSystemTrayIcon):
    def __init__(self, parent=None):
        QtGui.QSystemTrayIcon.__init__(self, parent)

        self.setIcon(QtGui.QIcon("icon.png"))

        self.iconMenu = QtGui.QMenu(parent)
        appabout = self.iconMenu.addAction("About")
        appexit = self.iconMenu.addAction("Exit")
        self.setContextMenu(self.iconMenu)

        # Remove this next line, it isn't needed
        #self.aboutdialog = QtGui.QWidget(parent)

        self.connect(appabout,QtCore.SIGNAL('triggered()'),self.showAbout)
        self.connect(appexit,QtCore.SIGNAL('triggered()'),self.appExit)

        # Remove this next line, it isn't needed
        #self.show()


    def showAbout(self):
        # Before showing the message box, disable the tray icon menu
        self.iconMenu.setEnabled(false)
        # Replace self.aboutdialog with the Python equivalent of null (0?)
        QtGui.QMessageBox.information(0, self.tr("About Tunarium"), self.tr("Your text here."))
        # Re-enable the tray icon menu
        self.iconMenu.setEnabled(true)

    def appExit(self):
        # Replace the next line with something that calls the QApplication's
        #   exit() or quit() function.
        #sys.exit()
        app.quit()


if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    # Tell the application not to exit when the last window is closed. This should 
    # prevent the application from exiting when the message box is closed.
    app.setQuitOnLastWindowClosed(false)

    trayIcon = SystemTrayIcon()
    trayIcon.show()

    sys.exit(app.exec_())

Update 2:

As requested, here is the equivalent C++ code:

main.cpp

#include <QtGui/QApplication>

#include "SystemTrayIcon.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    app.setQuitOnLastWindowClosed(false);
    SystemTrayIcon trayIcon(&app);
    trayIcon.show();

    return app.exec();
}

SystemTrayIcon.h

#ifndef SYSTEMTRAYICON_H
#define SYSTEMTRAYICON_H

#include <QtGui/QSystemTrayIcon>
#include <QtGui/QAction>
#include <QtGui/QMenu>
#include <QtGui/QWidget>

class SystemTrayIcon : public QSystemTrayIcon
{
    Q_OBJECT

public:
    SystemTrayIcon(QObject * parent = 0);
    virtual ~SystemTrayIcon();

private:
    QAction * m_appabout;
    QAction * m_appexit;
    QMenu * m_iconMenu;
    QWidget * m_aboutdialog;

private slots:
    void slot_showAbout();
    void slot_exit();
};

#endif  /* SYSTEMTRAYICON_H */

SystemTrayIcon.cpp

#include <iostream>
#include <QtCore/QCoreApplication>
#include <QtGui/QIcon>
#include <QtGui/QAction>
#include <QtGui/QMessageBox>

#include "SystemTrayIcon.h"

SystemTrayIcon::SystemTrayIcon(QObject * parent) :
    QSystemTrayIcon(parent),
    m_appabout(0),
    m_appexit(0),
    m_iconMenu(0),
    m_aboutdialog(0)
{
    setIcon(QIcon("icon.png"));

    m_iconMenu = new QMenu();
    m_appabout = m_iconMenu->addAction("About");
    m_appexit = m_iconMenu->addAction("Exit");
    setContextMenu(m_iconMenu);

    connect(m_appabout, SIGNAL(triggered()), this, SLOT(slot_showAbout()));
    connect(m_appexit, SIGNAL(triggered()), this, SLOT(slot_exit()));
}

SystemTrayIcon::~SystemTrayIcon()
{
}

void SystemTrayIcon::slot_showAbout()
{
    std::cout << "slot show about." << std::endl;
    m_iconMenu->setEnabled(false);
    QMessageBox::information(0, "About Tunarium", "Your text here.");
    m_iconMenu->setEnabled(true);
}

void SystemTrayIcon::slot_exit()
{
    std::cout << "slot exit." << std::endl;
    qApp->quit();
}

Answer 2

I need to access button in the QMessageBox window and add slot for the button. But I can't do it for now. That's what I've tryed. But it doesn't work.

self.aboutdialog = QtGui.QWidget()

reply = QtGui.QMessageBox.information(self.aboutdialog, self.tr("About Tunarium"), self.tr("Your text here."), QtGui.QMessageBox.Close)
        if reply == QtGui.QMessageBox.Close:
            self.aboutdialog.hide()