No paint event occurred on MainWindow

[andreaQt]

What i expect is a a window with 2 black sub window but when i run the program is windowed just the main window without the 2 black window.
What wrong i do or what i miss?
Code is attached.

[andreaQt]

Found Solution:
My mistake is that i created MainWindow class like QMainWindow but i have to create it like QWidget, after this change all go