Issues setting value of QDoubleSpinBox after connecting

Mad_Maniac

valuesetter.h:

#ifndef VALUESETTER_H
#define VALUESETTER_H

#include <QSlider>
#include <QSpinBox>
#include <QWidget>
#include <memory>

namespace Ui {
class ValueSetter;
}

class ValueSetter : public QWidget
{
    Q_OBJECT

public:
    explicit ValueSetter(QWidget *parent = nullptr);
    ~ValueSetter();

    void dpi(int dpi);
    void setValue(int value);
    void setDoubleValue(double value);
    void setMinimum(int minimum);
    void setMaximum(int maximum);

signals:
    void valueChanged(int);
    void valueChangedDouble(double);
    void minimumChanged(int);
    void maximumChanged(int);

private:
    double round2(double val);
    int val, min, max;

    int Dpi=72;
    Ui::ValueSetter *ui;
};

#endif // VALUESETTER_H

valuesetter.cpp:

#include "valuesetter.h"
#include "ui_valuesetter.h"

#include <QHBoxLayout>
#include <QVBoxLayout>
#include <string>
#include <QtMath>
#include <QDebug>

ValueSetter::ValueSetter(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::ValueSetter)
{
    ui->setupUi(this);
    setValue(0); setMinimum(0); setMaximum(1000*Dpi);
    connect(ui->slider,&QSlider::valueChanged,this,&ValueSetter::setValue);
    connect(ui->spinbox,static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),
            this,&ValueSetter::setDoubleValue);
}

ValueSetter::~ValueSetter()
{
    delete ui;
}

void ValueSetter::setValue(int value)
{
    qDebug() << ui->spinbox->maximum() << round2(round2(value)/round2(Dpi));
    ui->spinbox->setValue(round2(round2(value)/round2(Dpi)));
    ui->slider->setValue(value);
    emit valueChanged(value);
}

void ValueSetter::setDoubleValue(double value)
{
    ui->spinbox->setValue(value); ui->slider->setValue(static_cast<int>(value*Dpi));
    emit valueChangedDouble(value);
}

void ValueSetter::setMinimum(int min)
{
    ui->spinbox->setMinimum(static_cast<double>(min)/Dpi); ui->slider->setMinimum(min);
    emit minimumChanged(min);
}

void ValueSetter::setMaximum(int max)
{
    ui->spinbox->setMaximum(static_cast<double>(max)/Dpi); ui->slider->setMaximum(max); emit maximumChanged(max);
}

double ValueSetter::round2(double val)
{
    double value = static_cast<int>(100*val+0.5);
    return static_cast<double>(value/100);
}

valuesetter.ui:

In short, my problem is that when I try to move the QSlider, I get this set of errors, which I have a hard time resolving:

At first, the round2 in my valuesetter.cpp class was simply static_cast<double>. My guess was to test whether the error remained when I made sure there were only 2 decimal places, and it did. I don't think I implemented connect wrong, as there were no compiler errors or anything.

So I need help debugging.

Christian Ehrlicher

I would guess it's a stack overflow since QDoubleSpinBox::setValue() triggers QSlider::valueChanged. Take a look at the next calls by clicking on '<More>' and you'll see it.

hskoglund

Yes as @Christian-Ehrlicher says, it's overflowing :-( because the signals you connect to (the 2 valueChanged()) can be triggered either by a human clicking on the slider or the spinbox, or by your C++ code doing a ->setValue().

So when you drag the slider, your code sets a new value for the slider, which then sets a new value for the slider, etc etc in a forever loop :-(

One workaround is to neuter/silence the sliders/spinbox so that they only emit signals when a human clicks, not for C++ code. You can use the blockSignals(true) and blockSignals(false) for that, say like this:

...
void ValueSetter::setValue(int value)
{
    qDebug() << ui->spinbox->maximum() << round2(round2(value)/round2(Dpi));
 
    ui->spinbox->blockSignals(true);
    ui->spinbox->setValue(round2(round2(value)/round2(Dpi)));
    ui->spinbox->blockSignals(false);

    ui->slider->blockSignals(true);
    ui->slider->setValue(value);
    ui->slider->blockSignals(false);

    emit valueChanged(value);
}
...