How to make a Qt Widget grow with the window size?

I want to have a small QFormLayout that grows to fill its parent widget.

I created a new .ui file using the QWidget template in Qt Designer. I put a QFormLayout inside that 'window', then put some controls inside that QFormLayout.

This all works reasonably well, but the QFormLayout always stays at the size I set in Qt Designer. I would like the QFormLayout to fill its parent widget and grow/shrink with it.

How can I accomplish that?

In Designer, activate the centralWidget and assign a layout, e.g. horizontal or vertical layout. Then your QFormLayout will automatically resize.

Always make sure, that all widgets have a layout! Otherwise, automatic resizing will break with that widget!

See also

Controls insist on being too large, and won't resize, in QtDesigner