Setting behaviour in designer

[Morea]

Hi.
I work with the designer and now I wish to place two Layouts in the Mainwidget, one will be a vertical at the left side of the Mainwidget and it should keep a specific minimum width of, let's say 100 pixels, and the rest of the Mainwidget should be filled with the other Layout.
When resizing, the only thing that shouldn't change is the width of 100 pixels of the left layout, everything else should adapt to the size of the Mainwidget.

How can I set this behaviour in the designer?

[high_flyer]

just limit the widgets inside the fixed width layout to a fixed width.

[Morea]

And what about the size when I enlarge the mainwidget?

[high_flyer]

But you said:

When resizing, the only thing that shouldn't change is the width of 100 pixels of the left layout, everything else should adapt to the size of the Mainwidget.