QSpinBox enter NaN as a valid value

Question

I am trying to extend the QSpinBox to be able to enter "NaN" or "nan" as a valid value. According to the documentation i should use the textFromValue, valueFromText, and validate functions to accomplish this but i cant get it to work since its still not allowing me to enter any text besides numbers. Here is what i have in my .h and .cpp files:

CPP file:

#include "CustomIntSpinBox.h"

CustomIntSpinBox::CustomIntSpinBox(QWidget *parent) : QSpinBox(parent)
{
    this->setRange(-32767,32767);
}

QString CustomIntSpinBox::textFromValue(int value) const
{
    if (value == NAN_VALUE)
    {
        return QString::fromStdString("nan");
    }
    else
    {
        return QString::number(value);
    }
}

int CustomIntSpinBox::valueFromText(const QString &text) const
{
    if (text.toLower() == QString::fromStdString("nan"))
    {
        return NAN_VALUE;
    }
    else
    {
        return text.toInt();
    }
}

QValidator::State validate(QString &input, int pos)
{
    return QValidator::Acceptable;
}

H file:

#ifndef CUSTOMINTSPINBOX_H
#define CUSTOMINTSPINBOX_H

#include <QSpinBox>
#include <QWidget>
#include <QtGui>
#include <iostream>

using namespace std;

#define NAN_VALUE 32767

class CustomIntSpinBox : public QSpinBox
{
    Q_OBJECT

public:
    CustomIntSpinBox(QWidget *parent = 0);
    virtual ~CustomIntSpinBox() throw() {}

    int valueFromText(const QString &text) const;
    QString textFromValue(int value) const;
    QValidator::State validate(QString &input, int pos);
};

#endif // CUSTOMINTSPINBOX_H

Is there something im missing? or doing wrong? If theres and easier way to do this also that would be great to know...

Answer 1

The signature of QAbstractSpinBox::validate() is:

QValidator::State QAbstractSpinBox::validate ( QString & input, int & pos ) const

So your validate() method's signature differs in two ways: its not const, and you have int pos instead of int& pos. Thus it doesn't override QAbstractSpinBox::validate and is never called by QAbstractSpinBox.

Answer 2

If you can extend the lower bound of your range by -1 and use a normal QSpinBox or QDoubleSpinBox and call spinbox->specialValueText("nan"), which will show the string nan when value() == minimum(). The user won't be able to enter the string "nan" manually, but you can always accompany the spinbox with a button that executes spinbox->setValue(spinbox->minimum()). Here's a compilable example:

// main.cpp
#include <QSpinBox>
#include <QDoubleSpinBox>
#include <QDialog>
#include <QApplication>
#include <QVBoxLayout>

#include <limits>

class Tester : public QDialog {
    Q_OBJECT
public:
    static const int NanValue = -32767-1;
    explicit Tester(QWidget * parent=0)
        : QDialog(parent),
          m_spinBox(new QSpinBox(this)),
          m_doubleSpinBox(new QDoubleSpinBox(this))
    {
        QVBoxLayout * vlay = new QVBoxLayout(this);
        vlay->addWidget(m_spinBox);
        vlay->addWidget(m_doubleSpinBox);

        m_spinBox->setRange(NanValue,32767);
        m_doubleSpinBox->setRange(NanValue,32767);

        m_spinBox->setValue(NanValue);
        m_doubleSpinBox->setValue(NanValue);

        updateSpecialValueText();
    }

protected:
    void changeEvent(QEvent *e) {
        QDialog::changeEvent(e);
        if (e->type() == QEvent::LocaleChange)
            updateSpecialValueText();
    }


private:
    void updateSpecialValueText() {
        static const double NaN = std::numeric_limits<double>::quiet_NaN();
        m_spinBox->setSpecialValueText(locale().toString(NaN));
        m_doubleSpinBox->setSpecialValueText(locale().toString(NaN));
    }

private:
    QSpinBox * m_spinBox;
    QDoubleSpinBox * m_doubleSpinBox;
};

int main(int argc, char * argv[]) {
    QApplication app(argc, argv);

    Tester t;
    return t.exec();
}

#include "main.moc"

Answer 3

Maybe QSpinBox sets a lineEdit wich has a QIntValidator as QValidator. At least the docs of QAbstractSpinBox::setLineEdit suggest that the validator of the lineEdit has priority over the QAbstractSpinBox::validate function.