[Qt-interest] Mismatch between QSpinBox::textFromValue() documentation and actual behavior

[K. Frank]

Hello List -

(This is a follow-up on my previous posting, "How to make QSpinBox display
thousands separators?")

I am using Qt version 4.6.1 (as built on windows using TDM-2 mingw32 4.4.1).

I find that the behavior of QSpinBox::textFromValue() does not match
the documentation.


Copied from the documentation, .../doc/html/qspinbox.html#textFromValue:

QString QSpinBox::textFromValue ( int value ) const   [virtual protected]
This virtual function is used by the spin box whenever it needs to
display the given value. The default implementation returns a string
containing value printed in the standard way using
QWidget::locale().toString(). Reimplementations may return anything.
(See the example in the detailed description.)

Note: QSpinBox does not call this function for specialValueText() and
that neither prefix() nor suffix() should be included in the return
value.

If you reimplement this, you may also need to reimplement
valueFromText() and validate()

See also valueFromText() and validate().


At issue is that QWidget::locale().toString(int) formats integers with
thousands separators,
while QSpinBox::textFromValue(int) does not.

Concretely, the following class derived from QSpinBox gives us access
to the protected
QSpinBox::textFromValue(int).  (This class also overrides
textFromValue() to restore
the thousands separators.)


#include <QSpinBox>
class MySpinBox : public QSpinBox {
  Q_OBJECT
   public:
    MySpinBox (QWidget *parent = 0) : QSpinBox (parent) {}
    ~MySpinBox() {};
    QString getBaseTextFromValue (int value) const { return
QSpinBox::textFromValue (value); }
    QString getTextFromValue (int value) const { return textFromValue (value); }
  protected:
    QString textFromValue (int value) const { return locale().toString
(value); }
};


I load a MySpinBox with the value 10000.

   mySpinBox->value() returns 10000
   mySpinBox->getBaseTextFromValue (mySpinBox->value()) returns "10000"
   mySpinBox->locale().toString (mySpinBox->value()) returns "10,000"

I would have expected these last two to return the same string because
QSpinBox::textFromValue() -- called by MySpinBox::getBaseTextFromValue() --
should be equivalent to QWidget::locale().toString().

(Furthermore,

   mySpinBox->text() returns "10,000"
   mySpinBox->getTextFromValue (mySpinBox->value()) returns "10,000"

because these two resolve to MySpinBox::textFromValue(), the overridden
version of textFromValue() in my derived class.  So this is my solution to
getting thousands separators in my spin box.)

I don't know what the desired behavior is supposed to be, so I don't know
whether this is a documentation bug or and implementation bug.
(It's interesting to note that the documentation for
QDoubleSpinBox::textFromValue() states explicitly that thousands
separators are removed.)

(My personal preference for the behavior would be to support both the
presence and absence of thousands separators, presumably by
setting an options flag (or maybe in a tweak to locale), and not have
to resort to the minor effort of setting up a derived class.)

Thanks.


K. Frank