SIGSEGV with QMainWindow singleton - qt

Question

The application I am writting as unique instantiation of some classes which have to be accessible easily. For that i use singletons.
For exemple my Core is defined as :
class Core : public QObject
{
Q_OBJECT
public:
Core();
~Core();
static Core& getCore()
{
static Core mycore;
return mycore;
}
(...)
};
and it works just great. However I tried to do the same with my MainWindow class, which interits from QMainWindow. I need that in order to access methods such as geometry() from other objects
However Core works great, MainWindow makes error when clossing the programe. The main window destructor is called and executed apparently once ( debug using qDebug() ) but i still have a SIGSEGV signal. What's happening? How to solve it?
Here is the code of MainWindow
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
static MainWindow& getUi()
{
static MainWindow myUi;
return myUi;
}
public slots:
void refreshImage();
private:
Ui::MainWindow *ui;
};
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(&appCore(), SIGNAL(refreshed()), this, SLOT(refreshImage()));
}
MainWindow::~MainWindow()
{
delete ui;
}
And the main code
QApplication app(argc, argv);
try
{
appCore().setDevice(MDMA::Kinect);
appUi().show();
return app.exec();
} catch(MDMA::exn e) {
(...)
}
where appCore and appUi are macros for Core::getCore and MainWindow::getUi()

Answer 1

This crash probably results from your QApplication being destroyed before the MainWindow.
If you cannot pass your MainWindow via other ways to the code where it is needed (e.g. as argument or via QObjecg::parent()), you could employ a technique similar to what QApplication does with it's instance method (a non-owning global reference):
Construct your MainWindow as an ordinary local variable on the stack, after the QApplication. Then set a global pointer (maybe better a QPointer; e.g. a static member of MainWindow), which you initially initialize to 0, to this in the constructor of MainWindow. You can also check if it was already initialized here to enforce the uniqueness. Via a public accessor method (instance?) for the global pointer, you can access the class from everywhere while ensuring destruction before QApplication.

Answer 2

If you want to make singletone, try to use general technics, for example, as described here:
http://www.qtcentre.org/wiki/index.php?title=Singleton_pattern
Hope, lot of questions will dissappear after reading all of that article.
As for me, there is nice and simple realization of singletone.
Good luck!