Может это поможет:
bool QLayout::activate ()
Redoes the layout for parentWidget() if necessary.
You should generally not need to call this because it is automatically called at the most appropriate times. It returns true if the layout was redone.
See also update() and QWidget::updateGeometry().
Или это:
void QLayout::update ()
Updates the layout for parentWidget().
You should generally not need to call this because it is automatically called at the most appropriate times.
See also activate() and invalidate().
