Qt/C++ : Centralise parameters in one class - c++

Question

I'm trying to centralise some parameters in one class. I looked on several forums and tutorials without finding any real answer. Maybe I don't use Qt correctly.
I have a Qt class Application which handles theses parameters.
Application.h
class Application : public QApplication
{
public:
Application(int, char**);
~Application();
bool setFilesPath(QString path);
QString getFilesPath();
private:
QString filesPath;
}
main.cpp
int main(int argc, char *argv[])
{
Application app(argc, argv);
MainWindow mainWindow;
mainWindow.show();
return app.exec();
}
I'd like to access the setFilesPath() and getFilesPath() methods from everywhere (for exemple in another class. Therefore a made Application inherit from QApplication, hoping that qApp.setFilesPath() would work. But it doesnt.
It seems to be a quite usual thing to access some parameters from everywhere. So how could one do this ?
I've found this three ways :
Global variables
Static methods
Including an instance of Application in every class needing the method (but it seems wrong)
Which is more commonly used (and why) ? Why does my way doesn't work ?
Thank you.
EDIT:
In this topic, they use singelton design pattern.
So calling
Application *app = Application::getInstance();
everywhere I need it. Is it better ?

Answer 1

You can access your class using qApp pointer. According to the Qt documentation:
A global pointer referring to the unique application object. It is
equivalent to the pointer returned by the QCoreApplication::instance()
function except that, in GUI applications, it is a pointer to a
QApplication instance.
So, your code somewhere could look like:
Application *myApp = qobject_cast<Application *>(qApp);
QString path = myApp->getFilesPath();

Answer 2

You can have your classes in the main independently and connect a signal from each class that needs to access the value in your class to the slot that returns the value :
int main(int argc, char *argv[])
{
Application app(argc, argv);
MainWindow mainWindow;
MyClass myclass1;
QObject::connect(&mainWindow,SIGNAL(askFilesPath()),myclass1,SLOT(getFilesPath()));
mainWindow.show();
return app.exec();
}
This way when you call the signal askFilesPath() in your MainWindow, the slot in your custom class gets called and the value is returned:
QString filePath = askFilesPath();
You should note that if the two classes are in different threads then the connection type should be Qt::BlockingQueuedConnection.