QDoubleSpinBox with nonlinear values

I would like to create spinBox which would have a concrete list of values with alternating interval beetwen positions on it.

Something like that: 1.0, 5.0, 20.0, 35.0, 37.0, 39.0, 44.0, 50.0...

Is there a simple way to do it?

Hi !

You must reimplement virtual void QAbstractSpinBox::stepBy(int steps)

Here's a functionnal example :

Code:

---

#ifndef MYSPINBOX_H
#define MYSPINBOX_H
 
#include <QDoubleSpinBox>
 
class MySpinBox : public QDoubleSpinBox
{
    Q_OBJECT
public:
    explicit MySpinBox(QWidget *parent = 0) : QDoubleSpinBox(parent)
    {
        _values<<1.0<<5.0<<20.0<<35.0<<37.0<<39.0<<44.0<<50.0;
        setRange(_values.first(),_values.last());
    }
 
    void stepBy(int steps)
    {
        int idx = findIdx(value());
        idx += steps>0 ? 1:-1;
        setValue(_values.value(idx));
    }
 
private:
    QList<double> _values;
 
    int findIdx(double  currVal)
    {
        for(int idx = 0 ; idx < _values.count()-1 ; ++idx)
            if(currVal>=_values.value(idx) && currVal<_values.value(idx+1)) return idx;
 
        return  _values.count()-1;
    }
};
 
#endif // MYSPINBOX_H

---

... my first answer on this forum ! ...

Wow, it looks great. I can't write such an concise and elegant code so far. Thanks.

A couple of comments, if I may:

1. Qt provides a lookup function for QList: QList::indexOf()
2. But, the lookup is unnecessary if you make idx a member variable and increment it:

Code:

---

class MySpinBox : public QDoubleSpinBox
{
    Q_OBJECT
public:
    explicit MySpinBox(QWidget *parent = 0) : QDoubleSpinBox(parent), _idx(0)
    {
        values<<1.0<<5.0<<20.0<<35.0<<37.0<<39.0<<44.0<<50.0;
        setRange(values.first(),values.last());
    }
 
    void stepBy(int steps)
    {
        _idx += steps;
        setValue(_values.at(_idx));
    }
 
private:
    QList<double> _values;
    int _idx;
};

---

Hope this helps!

Range checking/clamping of idx might be a good idea. Crashes in debug mode if you Shift-PgUp for example. Doesn't crash in release mode but fails to operate correctly for me: e.g. press Shift-PgUp and then up arrow and you run through:

Code:

---

//_idx  _value.at(_idx)
10 6.71656e-317 
11 3.95253e-323 
12 6.71634e-317 
13 4.44659e-323 
14 3.21143e-322 
15 6.95315e-310 
16 4.88059e-313

---

where the index and data are rubbish. The up-arrow does not appear to function any longer and down remains unavailable.

You're right Chris. I just "winged it" on this one as evidenced by the values/_values typo.

Revised:

Code:

---

class MySpinBox : public QDoubleSpinBox
{
    Q_OBJECT
public:
    explicit MySpinBox(QWidget *parent = 0) : QDoubleSpinBox(parent), _idx(0)
    {
        _values<<1.0<<5.0<<20.0<<35.0<<37.0<<39.0<<44.0<<50.0;
        setRange(_values.first(),_values.last());
    }
 
    void stepBy(int steps)
    {
        _idx += steps;
        if(_idx<0) _idx=0;
        else    if(_idx>=_values.count()) _idx=_values.count()-1;
        setValue(_values.at(_idx));
    }
 
private:
    QList<double> _values;
    int _idx;
};

---