How to receive mouse events for QDoubleSpinBox

JonB

@shreya_agrawal
Have you investigated something based on:

for (QWidget *child: spinBox.findChildren<QWidget *>())
    child->installEventFilter(this);

I am not sure whether the buttons you want are widgets or (as may well be the case) simply drawn as part of the style. The above will at least show where actual widgets are.

shreya_agrawal

@JonB
Thank you for your reply!
Actually the only child the spin box returns is its line edit, not the up and down buttons.

JonB

@shreya_agrawal
Yes, I think I read that. Sadly it means the arrows are just drawn as part of the style, they are not widgets you can connect to. Which should mean click is recognised by coordinates internally in spinbox code. Not what you wanted. You might examine Qt source code if you really need to know how it does it. It does sound as though working on valueChanged(), which the internal code must resolve via mouse position relative to arrow drawing, would be the simplest "high level" approach if you want to avoid duplicating internal coordinate calculation.

shreya_agrawal

@JonB
Okay, I will look into it further and post if I reach somewhere.

Christian Ehrlicher

override mousePressEvent and get the positions of the spinboxes through the style with subElementRect() - this is what QAbstractSpinBox is doing

JonB

@shreya_agrawal
I've had a look at the on-line source (I don't have source files myself). Although I haven't gone all the way the through, the gist seems to be that Qt notes whether you mouse down on what it maintains as an internal "hover control", which will be the up arrow, down arrow or nothing.

The relevant functions are https://codebrowser.dev/qt6/qtbase/src/widgets/widgets/qabstractspinbox.cpp.html#_ZN16QAbstractSpinBox15mousePressEventEP11QMouseEvent

void QAbstractSpinBox::mousePressEvent(QMouseEvent *event)
{
    Q_D(QAbstractSpinBox);
    d->keyboardModifiers = event->modifiers();
    if (event->button() != Qt::LeftButton || d->buttonState != None) {
        return;
    }
    d->updateHoverControl(event->position().toPoint());
    event->accept();
    const StepEnabled se = (d->buttonSymbols == NoButtons) ? StepEnabled(StepNone) : stepEnabled();
    if ((se & StepUpEnabled) && d->hoverControl == QStyle::SC_SpinBoxUp) {
        d->updateState(true);
    } else if ((se & StepDownEnabled) && d->hoverControl == QStyle::SC_SpinBoxDown) {
        d->updateState(false);
    } else {
        event->ignore();
    }
}

and the call to d->updateHoverControl(event->position().toPoint()); https://codebrowser.dev/qt6/qtbase/src/widgets/widgets/qabstractspinbox.cpp.html#_ZN23QAbstractSpinBoxPrivate18updateHoverControlERK6QPoint

/*!
    \internal
    Updates the old and new hover control. Does nothing if the hover
    control has not changed.
*/
bool QAbstractSpinBoxPrivate::updateHoverControl(const QPoint &pos)
{
    Q_Q(QAbstractSpinBox);
    QRect lastHoverRect = hoverRect;
    QStyle::SubControl lastHoverControl = hoverControl;
    bool doesHover = q->testAttribute(Qt::WA_Hover);
    if (lastHoverControl != newHoverControl(pos) && doesHover) {
        q->update(lastHoverRect);
        q->update(hoverRect);
        return true;
    }
    return !doesHover;
}
/*!
    \internal
    Returns the hover control at \a pos.
    This will update the hoverRect and hoverControl.
*/
QStyle::SubControl QAbstractSpinBoxPrivate::newHoverControl(const QPoint &pos)
{
    Q_Q(QAbstractSpinBox);
    QStyleOptionSpinBox opt;
    q->initStyleOption(&opt);
    opt.subControls = QStyle::SC_All;
    hoverControl = q->style()->hitTestComplexControl(QStyle::CC_SpinBox, &opt, pos, q);
    hoverRect = q->style()->subControlRect(QStyle::CC_SpinBox, &opt, hoverControl, q);
    return hoverControl;
}

So ultimately I think it relies on

    hoverControl = q->style()->hitTestComplexControl(QStyle::CC_SpinBox, &opt, pos, q);
    hoverRect = q->style()->subControlRect(QStyle::CC_SpinBox, &opt, hoverControl, q);

to find the location of the arrow buttons. And https://codebrowser.dev/qt6/qtbase/src/widgets/widgets/qabstractspinbox.cpp.html#_ZNK16QAbstractSpinBox15initStyleOptionEP19QStyleOptionSpinBox includes

    if (d->buttonSymbols != QAbstractSpinBox::NoButtons) {
        option->subControls |= QStyle::SC_SpinBoxUp | QStyle::SC_SpinBoxDown;
        if (d->buttonState & Up) {
            option->activeSubControls = QStyle::SC_SpinBoxUp;
        } else if (d->buttonState & Down) {
            option->activeSubControls = QStyle::SC_SpinBoxDown;
        }

so this is to do with recognising which button ultimately.

So like I said unless you want to replicate this (see QStyle for some of the calls) it would be easier for you to react to the generated valueChanged() signal.

JonB

@Christian-Ehrlicher said in How to receive mouse events for QDoubleSpinBox:

override mousePressEvent and get the positions of the spinboxes through the style with subElementRect() - this is what QAbstractSpinBox is doing

Ooohh, you posted this while I was doing all my source code searching! Not sure how your subElementRect() relates to the subControlRect() I have come across in the code above.

JonB

@shreya_agrawal
Ah ha! I little Googling leads me to QSpinbox Check if up or down button is pressed which seems to give the relatively simple code

class SpinBox(QSpinBox):
    upClicked = pyqtSignal()
    downClicked = pyqtSignal()

    def mousePressEvent(self, event):
        super().mousePressEvent(event)

        opt = QStyleOptionSpinBox()
        self.initStyleOption(opt)

        control = self.style().hitTestComplexControl(
            QStyle.CC_SpinBox, opt, event.pos(), self
        )
        if control == QStyle.SC_SpinBoxUp:
            self.upClicked.emit()
        elif control == QStyle.SC_SpinBoxDown:
            self.downClicked.emit()

@eyllanesc's answers & code are usually good, so it may be this simple.

shreya_agrawal

@JonB
Well thank you for sparing so much of your time!
Sadly, the Qt version I am using does not support the use of SC_SpinBoxUp and SC_SpinBoxDown subcontrols :(
I think I will have to rely on the valueChanged() signal for now.

JonB

@shreya_agrawal said in How to receive mouse events for QDoubleSpinBox:

Sadly, the Qt version I am using does not support the use of SC_SpinBoxUp and SC_SpinBoxDown subcontrols :(

Pardon? State your exact Qt version. Since it is available in Qt4, 5, 6 I doubt your statement.
Show the code you have tried and the error message you get. Don't forget that Python's QStyle.SC_SpinBoxUp is C++'s QStyle::SC_SpinBoxUp....

shreya_agrawal

@JonB
Qt Version: Qt Creator 4.12.2 Based on Qt 5.14.2 (GCC 5.3.1 20160406 (Red Hat 5.3.1-6), 64 bit)

Line of code: QRect downButtonRect = spinBox->style()->subElementRect(QStyle::SE_SpinBoxDown, spinBox);

Error Message: no member named 'SE_SpinBoxDown' in 'QStyle'

JonB

@shreya_agrawal
Why don't you copy from both the original code and what I wrote, instead of typing it on yourself and as we can see getting it wrong/misspelt...? That's why copy & paste exists.

shreya_agrawal

@JonB
Oops! My Bad :)
The solution worked. Thank you for your patience.