Qt - Non Modal Dialog before Main Window is created - c++

Question

I've been struggling to do this : I want to show on a window a QWidget, or a QDialog before the MainWindow is created, but I cannot use exec() because it will enter its loop and won't create my MainWindow before I accept or reject the dialog.
The reason I want to do this is to have a widget showing information while the MainWindow constructs itself. I don't want to keep this extra window once the MainWindow is showing up.
I believe the issue comes from the fact that the main window is already created when a.exec() is called and the window won't show up before a.exec(). The solution I found is to use a QDialog instead and call exec() but it blocks the rest of the code which I don't want to happen.
Code :
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
StartUpDialog start; //this is my custom QDialog, can be a QWidget if necessary.
qDebug() << "starting up!";
MainWindow w;
start.exec(); //I tried show() but it won't show up.
w.startApp(&start); //this function will do some stuff.
w.show();
//I don't want start to stay after mainwindow shows up
return a.exec();
}
Here is what I tried so far :
I tried to create and show the StartUpDialog while constructing the MainWindow but it won't work out.
Use start.show(), but it won't show before the mainwindow does, both for a QWidget and a QDialog.
Use start.exec(), this does what I want but it's modal and I couldn't make it non-modal with SetModal(false) or setWindowModality(Qt:NonModal).
I also tried to use start.exec() and attempted to reimplement accepted() and exec() so that it automatically calls accepted() as soon as it appears but it will still close the window.
Hopefully you can help me in that issue, and thanks for reading !
UPDATE : Solved thanks to Trap, here is how I made it :
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
StartUpDialog start;
QSplashScreen *splash = new QSplashScreen();
StartUpWidget *start = new StartUpWidget(splash);
splash->resize(350,380);
start->show();
splash->raise();
splash->show();
qDebug() << "starting up!";
MainWindow w;
w.startApp(start);
w.show();
splash->finish(&w);
start->deleteLater();
splash->deleteLater();
return a.exec();
}
My only concern is that I use a Gif inside my widget using QMovie and updating it has to be done manually apparently.

Answer 1

If I understand your problem correctly (showing a dialog until your main window is created), you should have a look at the QSplashScreen class : http://doc.qt.io/qt-5/qsplashscreen.html