Adjust verticalLayout to centralWidget size ?

[antismap]

Hello, I'm a begginer with Qt and since a few hours i'm stuck : How do i ajust the size of a vertical layout (or whatever else) into the centralwidget size ? I would like to be set to the current window size (the Mainwindow and centralWidget size)
I'm using the designer. The objects are like this :

@
MainWindow
centralWidget
verticalLayout
@

I've been searching various forums and doc but I can't find the answer,
Thanks in advance !

[EDIT: @-tags for formatting, Volker]

[vinb]

You have to layout not only the widgets on the mainwindow, but also the mainwindow itself

[antismap]

Oh my god, I've read your sentence, i clicked two times and you saved me ! Many thanks :)