Simple MainWindow Problem :)

[Walux]

I have a QWidget Class and a QMainWindow Class , designed with Qt Designer .
In the main , i called the widget to show , no problem , and i connected one button to show the MainWindow , but when i click the button , the main window appears in a flash then disappears .

I'll be grateful for your help.

[Walux]

It's alright , i fixed it .
All i had to do was add a private instance of my mainWindow class in my widget's header .

But i'll still b happy to know the reason why it worked now , and didn't work before :)