QT4: Is it possible to make a QListView scroll smoothly?

I have a QlistWidget* in ui->barra_scroll and I feel very smooth with this.

QScrollBar *qsb = ui->barra_scroll->verticalScrollBar();
qsb->setSingleStep(5);

If I understand your question correctly you would like to redefine the scrolling behavior of the widget. I guess what happens is that listview is getting scrolled by the item's height whenever users hits a scroll arrow (marked as b on the image below).

For a vertical scroll bar connected to a list view, scroll arrows typically move the current position one "line" up or down, and adjust the position of the slider by a small amount. I believe line in this case it is an icon's height. You can adjust items height by installing and item delegate (setItemDelegate) and overriding its sizeHint method. Though this would not help you to solve this problem. What you could try is to create a QListView descendant and override its updateGeometries method. There you can setup the vertical scrollbar step to the value you want, I guess 1 or 2 for this task. Below is an example of the custom listview:

class TestListView : public QListView
{
Q_OBJECT
public:
    explicit TestListView(QWidget *parent = 0);

protected:
    virtual void updateGeometries();
};

TestListView::TestListView(QWidget *parent) :
    QListView(parent)
{
    //???
}

void TestListView::updateGeometries()
{
    QListView::updateGeometries();
    verticalScrollBar()->setSingleStep(2);
}

hope this helps, regards

Maybe QListView.setVerticalScrollMode(QAbstractItemView::ScrollPerPixel)