qt - QMainWindow: size management of central widget and dock widgets -

i want mainwindow keep approximate ratio of dock widget sizes , central widget size, when window's size changed. i've written simplest mainwindow central widget , 6 dock widgets:

#include <qplaintextedit> #include <qdockwidget>  #include "mainwindow.h"  mainwindow::mainwindow(qwidget *parent) :     qmainwindow(parent) {     this->setgeometry(20, 20, 600, 600);      this->setcentralwidget(           new qplaintextedit("central", this)           );      qdockwidget *p_dw;      (int = 0; < 6; ++i){        p_dw = new qdockwidget("dock " + qstring::number(i));         p_dw->setwidget(              new qplaintextedit("dock " + qstring::number(i), this)              );         qt::dockwidgetarea area;        switch (i){           case 0:           case 1:              area = qt::topdockwidgetarea;              break;           case 2:              area = qt::rightdockwidgetarea;              break;           case 3:           case 4:              area = qt::bottomdockwidgetarea;              break;           default:              area = qt::leftdockwidgetarea;              break;        }         adddockwidget(area, p_dw);     } }  mainwindow::~mainwindow() { } 

when started, looks follows:

i can shrink it:

and expand back, , after expanded, looks @ first screenshot. fine.

the problem if user "touches" central widget bounds (i mean, changes central widget size manually, ever little bit), main window changes policy dramatically: after user touches central widget, shrinks window, , expands back, dockwidgets have minimum sizes:

the question is, how prevent behavior? or, more generally, how can influence on size policy of qmainwindow? can't find documentation behaviour i've explained above.