QSpinBox inside a QScrollArea: How to prevent Spin Box from stealing focus when scrolling?

Try removing Qt::WheelFocus from the spinbox' QWidget::focusPolicy:

spin->setFocusPolicy( Qt::StrongFocus );

In addition, you need to prevent the wheel event from reaching the spinboxes. You can do that with an event filter:

explicit Widget( QWidget * parent=0 )
    : QWidget( parent )
{
    // setup ...
    Q_FOREACH( QSpinBox * sp, findChildren<QSpinBox*>() ) {
        sp->installEventFilter( this );
        sp->setFocusPolicy( Qt::StrongFocus );
    }

}

/* reimp */ bool eventFilter( QObject * o, QEvent * e ) {
    if ( e->type() == QEvent::Wheel &&
         qobject_cast<QAbstractSpinBox*>( o ) )
    {
        e->ignore();
        return true;
    }
    return QWidget::eventFilter( o, e );
}

---

edit from Grant Limberg for completeness as this got me 90% of the way there:

In addition to what mmutz said above, I needed to do a few other things. I had to create a subclass of QSpinBox and implement focusInEvent(QFocusEvent*) and focusOutEvent(QFocusEvent*). Basically, on a focusInEvent, I change the Focus Policy to Qt::WheelFocus and on the focusOutEvent I change it back to Qt::StrongFocus.

void MySpinBox::focusInEvent(QFocusEvent*)
{
     setFocusPolicy(Qt::WheelFocus);
}

void MySpinBox::focusOutEvent(QFocusEvent*)
{
     setFocusPolicy(Qt::StrongFocus);
}

Additionally, the eventFilter method implementation in the event filter class changes its behavior based on the current focus policy of the spinbox subclass:

bool eventFilter(QObject *o, QEvent *e)
{
    if(e->type() == QEvent::Wheel &&
       qobject_cast<QAbstractSpinBox*>(o))
    {
        if(qobject_cast<QAbstractSpinBox*>(o)->focusPolicy() == Qt::WheelFocus)
        {
            e->accept();
            return false;
        }
        else
        {
            e->ignore();
            return true;
        }
    }
    return QWidget::eventFilter(o, e);
}

In order to solve this, we need to care about the two following things:

1. The spin box mustn't gain focus by using the mouse wheel. This can be done by setting the focus policy to Qt::StrongFocus.
2. The spin box must only accept wheel events if it already has focus. This can be done by reimplementing QWidget::wheelEvent within a QSpinBox subclass.

Complete code for a MySpinBox class which implements this:

class MySpinBox : public QSpinBox {

    Q_OBJECT

public:

    MySpinBox(QWidget *parent = 0) : QSpinBox(parent) {
        setFocusPolicy(Qt::StrongFocus);
    }

protected:

    virtual void wheelEvent(QWheelEvent *event) {
        if (!hasFocus()) {
            event->ignore();
        } else {
            QSpinBox::wheelEvent(event);
        }
    }
};

That's it. Note that if you don't want to create a new QSpinBox subclass, then you can also use event filters instead to solve this.

My attempt at a solution. Easy to use, no subclassing required.

First, I created a new helper class:

#include <QObject>

class MouseWheelWidgetAdjustmentGuard : public QObject
{
public:
    explicit MouseWheelWidgetAdjustmentGuard(QObject *parent);

protected:
    bool eventFilter(QObject* o, QEvent* e) override;
};

#include <QEvent>
#include <QWidget>

MouseWheelWidgetAdjustmentGuard::MouseWheelWidgetAdjustmentGuard(QObject *parent) : QObject(parent)
{
}

bool MouseWheelWidgetAdjustmentGuard::eventFilter(QObject *o, QEvent *e)
{
    const QWidget* widget = static_cast<QWidget*>(o);
    if (e->type() == QEvent::Wheel && widget && !widget->hasFocus())
    {
        e->ignore();
        return true;
    }

    return QObject::eventFilter(o, e);
}

Then I set the focus policy of the problematic widget to StrongFocus, either at runtime or in Qt Designer. And then I install my event filter:

ui.comboBox->installEventFilter(new MouseWheelWidgetAdjustmentGuard(ui.comboBox));

Done. The MouseWheelWidgetAdjustmentGuard will be deleted automatically when the parent object - the combobox - is destroyed.