ScrollArea in a tabWidget

[Yaoming]

I've tried to do it on Designer but it doesn't work. My problem is: I add some textEdits which have my qtabWidget as "parent". Those textEdit grow bigger each time you add text in them (so that you always see the full text). But when they are bigger than the qtabwidget (they need to be because the user needs to have plenty of space to be able to write a lot of things) I would like my QTabWidget to display a vertical scrollbar so that the user can see what he has been writing.
My problem with designer is that the scrollArea is that it doesn't take my qtabWidget size (it's not taking the entire tabs and it doesn't display the scrollbars).
My problem with my code is that I've got to create a new Tab to make the scrollArea take the entire size of my tab and it's not working. On top of that I'd like my background to be white and not grey as it is when I compile. Here's a screenshot of what I have:

with designer: reza.jpg
with my code: aze.jpg