resizing widget inside QScrollArea

[mastupristi]

I have a QScrollArea, and I want the widget inside its viewPort to be resized to the maximum viewport size.
I have my class Dialog derived from QDialog and I have redefined resizeEvent() method, as follows:

#include <QVBoxLayout>
 
Dialog::Dialog(QWidget *parent)
    : QDialog(parent)
{
    sa = new QScrollArea(this);
    sa->setMinimumSize(400,300);
    sa->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
    sa->setVerticalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );
    sa->setHorizontalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );
 
    qd = new QDial(this);
    qd->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
    sa->setWidget(qd);
 
    QVBoxLayout *mainLayout = new QVBoxLayout();
    mainLayout->addWidget(sa);
 
    setLayout(mainLayout);
}
 
Dialog::~Dialog()
{
    delete qd;
    delete sa;
    delete layout();
}
 
#include <cstdio>
 
void Dialog::resizeEvent ( QResizeEvent * event )
{
    qd->resize(sa->viewport()->contentsRect().size());
 
    QString str;
    str = "sa->viewport()->contentsRect().size() " + QString::number(sa->viewport()->contentsRect().size().width()) + "," + QString::number(sa->viewport()->contentsRect().size().height());
    printf("%s\n", str.toAscii().constData());
}

#include <QVBoxLayout>

Dialog::Dialog(QWidget *parent)
    : QDialog(parent)
{
    sa = new QScrollArea(this);
    sa->setMinimumSize(400,300);
    sa->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
    sa->setVerticalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );
    sa->setHorizontalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );

    qd = new QDial(this);
    qd->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
    sa->setWidget(qd);

    QVBoxLayout *mainLayout = new QVBoxLayout();
    mainLayout->addWidget(sa);

    setLayout(mainLayout);
}

Dialog::~Dialog()
{
    delete qd;
    delete sa;
    delete layout();
}

#include <cstdio>

void Dialog::resizeEvent ( QResizeEvent * event )
{
    qd->resize(sa->viewport()->contentsRect().size());

    QString str;
    str = "sa->viewport()->contentsRect().size() " + QString::number(sa->viewport()->contentsRect().size().width()) + "," + QString::number(sa->viewport()->contentsRect().size().height());
    printf("%s\n", str.toAscii().constData());
}

To copy to clipboard, switch view to plain text mode 

Once started I expect the QDial to be resized to viewPort size, but I obtain the following:

And on the console it is wrote:

sa->viewport()->contentsRect().size() 96,26

as if the QScrollArea was something like 100x30. But if I try to resize all works, so the piece of code in resizeEvent() works.

What is wrong? Where is the mistake?
I also attach the project

thanks