duplicate execution of QSpinBox arrow click when followed by long computation

Joachim W

Under Linux, clang5, Qt5.10, the following misbehaviour is quite reproducible:

If a QSpinBox or QDoubleSpinBox is connected to a function that takes longer than about 0.5 seconds, then a single click on an up or down arrow is followed by a second incrementation and a second execution of the connected function.

Minimal example:

int delay = 600;
auto* test = new QSpinBox;
connect(test, _SLOT_(QSpinBox, valueChanged, int), [this](int val) {
        qDebug() << "GOT VALUE " << val;
        QThread::msleep(delay);
        qDebug() << "WOKE UP "; });

One single click on the "up" arrow will cause the following:

GOT VALUE 1
[delay]
WOKE UP
GOT VALUE 2
[delay]
WOKE UP

Whereas with t of about 500 or smaller, I get the expected

GOT VALUE 1
[delay]
WOKE UP

What could be the cause? How to further analyze?

VRonin

If you stop it for longer it will probably increase by even more that 1.
You are blocking the event loop before it process the QEvent::MouseButtonRelease so it behaves like if you are holding the mouse button down.
Try:

int delay = 600;
auto* test = new QSpinBox;
connect(test, QOverload<int>::of(&QSpinBox::valueChanged), test, [delay](int val) {
        qDebug() << "GOT VALUE " << val;
        QThread::msleep(delay);
        qDebug() << "WOKE UP "; }, Qt::QueuedConnection);

Joachim W

Try: ...

Tried. Still incrementing twice.

Joachim W

So upon QSpinBox::valueChanged, I ought to wait for QEvent::MouseButtonRelease?

That would have no undesirable side effects?

Is there some example code?

VRonin

The problem is definetly what I described but 1 event loop cycle is not enough to capture the release.
This solves it but I agree it's ugly

#include <QApplication>
#include <QStyle>
#include <QTimer>
#include <QDebug>
#include <QThread>
#include <QSpinBox>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QSpinBox wid;
    QObject::connect(&wid, QOverload<int>::of(&QSpinBox::valueChanged), &wid, [&wid](int val) {
            QTimer::singleShot(1+qMax(
                wid.style()->styleHint(QStyle::SH_SpinBox_ClickAutoRepeatRate, 0, &wid)
                ,wid.style()->styleHint(QStyle::SH_SpinBox_ClickAutoRepeatThreshold, 0, &wid)
            ),&wid,[val](){
                qDebug() << "GOT VALUE " << val;
                QThread::msleep(600);
                qDebug() << "WOKE UP ";
            });

    });
    wid.show();
    return a.exec();
}

Christian Ehrlicher

This could be the same as in QTBUG-14259