Resizing all the QWidgets while resizing the main window

[AL]

Hello,
I have a main window with lots of widgets on it (moreover Qlabels with images, buttons, checkboxes, ...). I would like to resize all of them (proportionally) automatically while the main window is resized.

For example: I have a mainwindow with a QLabel (with a png image in it) and this label width and height take the 50% of the main window, I would like that, when I resize the main window to any size, the QLabel width and height will be always the 50% of the main window (and obviously the image has to stretch)

How can I do that?

Tx!