How to change QMainWindow size at runtime?

[myfifth]

I've found the root cause

QSize QWidgetPrivate::adjustedSize() const
{
    Q_Q(const QWidget);
 
    QSize s = q->sizeHint();
 
    if (q->isWindow()) {
        Qt::Orientations exp;
        if (layout) {
            if (layout->hasHeightForWidth())
                s.setHeight(layout->totalHeightForWidth(s.width()));
            exp = layout->expandingDirections();
        } else
        {
            if (q->sizePolicy().hasHeightForWidth())
                s.setHeight(q->heightForWidth(s.width()));
            exp = q->sizePolicy().expandingDirections();
        }
        if (exp & Qt::Horizontal)
            s.setWidth(qMax(s.width(), 200));
        if (exp & Qt::Vertical)
            s.setHeight(qMax(s.height(), 100));
#if defined(Q_WS_X11)
        QRect screen = QApplication::desktop()->screenGeometry(q->x11Info().screen());
#else // all others
        QRect screen = QApplication::desktop()->screenGeometry(q->pos());
#endif
#if defined (Q_WS_WINCE) || defined (Q_OS_SYMBIAN)
        s.setWidth(qMin(s.width(), screen.width()));
        s.setHeight(qMin(s.height(), screen.height()));
#else
        s.setWidth(qMin(s.width(), screen.width()*2/3));
        s.setHeight(qMin(s.height(), screen.height()*2/3));
#endif
        if (QTLWExtra *extra = maybeTopData())
            extra->sizeAdjusted = true;
    }
 
    if (!s.isValid()) {
        QRect r = q->childrenRect(); // get children rectangle
        if (r.isNull())
            return s;
        s = r.size() + QSize(2 * r.x(), 2 * r.y());
    }
 
    return s;
}

QSize QWidgetPrivate::adjustedSize() const
{
    Q_Q(const QWidget);

    QSize s = q->sizeHint();

    if (q->isWindow()) {
        Qt::Orientations exp;
        if (layout) {
            if (layout->hasHeightForWidth())
                s.setHeight(layout->totalHeightForWidth(s.width()));
            exp = layout->expandingDirections();
        } else
        {
            if (q->sizePolicy().hasHeightForWidth())
                s.setHeight(q->heightForWidth(s.width()));
            exp = q->sizePolicy().expandingDirections();
        }
        if (exp & Qt::Horizontal)
            s.setWidth(qMax(s.width(), 200));
        if (exp & Qt::Vertical)
            s.setHeight(qMax(s.height(), 100));
#if defined(Q_WS_X11)
        QRect screen = QApplication::desktop()->screenGeometry(q->x11Info().screen());
#else // all others
        QRect screen = QApplication::desktop()->screenGeometry(q->pos());
#endif
#if defined (Q_WS_WINCE) || defined (Q_OS_SYMBIAN)
        s.setWidth(qMin(s.width(), screen.width()));
        s.setHeight(qMin(s.height(), screen.height()));
#else
        s.setWidth(qMin(s.width(), screen.width()*2/3));
        s.setHeight(qMin(s.height(), screen.height()*2/3));
#endif
        if (QTLWExtra *extra = maybeTopData())
            extra->sizeAdjusted = true;
    }

    if (!s.isValid()) {
        QRect r = q->childrenRect(); // get children rectangle
        if (r.isNull())
            return s;
        s = r.size() + QSize(2 * r.x(), 2 * r.y());
    }

    return s;
}

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The root was that window has a default size policy, so adjustSize() never ran into using childrenRect to expand size. How could I avoid to it?

---

Added after 4 minutes:

You have to resize() your mainwindow, not the frame inside it. And calling adjustSize() destroy all other setting you made before.

but I can't get the total size of frame plus other bars (toolbar, menubar, etc).