QSpinBox with Unsigned Int for Hex Input

The result is pretty simple, and it works well. Sharing here in case anyone else can benefit from this. It has a 32bit mode and a 16bit mode.

class HexSpinBox : public QSpinBox
{
public:
    HexSpinBox(bool only16Bits, QWidget *parent = 0) : QSpinBox(parent), m_only16Bits(only16Bits)
    {
        setPrefix("0x");
        setDisplayIntegerBase(16);
        if (only16Bits)
            setRange(0, 0xFFFF);
        else
            setRange(INT_MIN, INT_MAX);
    }
    unsigned int hexValue() const
    {
        return u(value());
    }
    void setHexValue(unsigned int value)
    {
        setValue(i(value));
    }
protected:
    QString textFromValue(int value) const
    {
        return QString::number(u(value), 16).toUpper();
    }
    int valueFromText(const QString &text) const
    {
        return i(text.toUInt(0, 16));
    }
    QValidator::State validate(QString &input, int &pos) const
    {
        QString copy(input);
        if (copy.startsWith("0x"))
            copy.remove(0, 2);
        pos -= copy.size() - copy.trimmed().size();
        copy = copy.trimmed();
        if (copy.isEmpty())
            return QValidator::Intermediate;
        input = QString("0x") + copy.toUpper();
        bool okay;
        unsigned int val = copy.toUInt(&okay, 16);
        if (!okay || (m_only16Bits && val > 0xFFFF))
            return QValidator::Invalid;
        return QValidator::Acceptable;
    }

private:
    bool m_only16Bits;
    inline unsigned int u(int i) const
    {
        return *reinterpret_cast<unsigned int *>(&i);
    }
    inline int i(unsigned int u) const
    {
        return *reinterpret_cast<int *>(&u);
    }

};

If you don't need full 32 bits you can do it very simply like this:

#pragma once

#include <QSpinBox>

class PaddedSpinBox : public QSpinBox
{
public:
    PaddedSpinBox(QWidget *parent = 0) : QSpinBox(parent)
    {
    }
protected:
    QString textFromValue(int value) const override
    {
        // Pad to the width of maximum().
        int width = QString::number(maximum(), displayIntegerBase()).size();
        return QString("%1").arg(value, width, displayIntegerBase(), QChar('0')).toUpper();
    }
};

In the form designer (or whatever) then you just set:

• prefix: 0x
• displayIntegerBase: 16
• maximum: 255 (or whatever)

If you need full 32 bits you will have to employ casting tricks, or maybe just use a line edit.