Why is the window disappearing?

Question

Qt

Hello! I create a dialog box on top of the standard MainWindow in the QT environment. I declare it Dialog dlg and call it dlg.show(), but it appears and disappears immediately, what could be the reason?

Answer 1

For dialogs, call not show() as you would for a regular widget, but exec():
dlg.exec().

Answer 2

With the fact that when you exit the scope of the dlg instance, the window is destroyed along with the instance. Create a dlg on the heap:
Dialog* dlg=new Dialog(...);
dlg->show();