[Qt-interest] QDate representation in QCombobox

[Petric Frank]

Hello,

On Friday, 23. July 2010 00:39:10 Anders Bakken wrote:
> On Thu, Jul 22, 2010 at 03:42:47AM +0100, Petric Frank wrote:
> > Hello,
> > 
> > i have a model (QSqlTableModel) set to an instance of QCombox
> > (->setModel). This comboc box is configured to be not editable.
> > 
> > >From the model i select a column which represents a date and passed it
> > >to the
> > 
> > combo box instance. I've verified that the data returned from the model
> > is of type QVariant::Date.
> > 
> > For the QComboBox instance i set the delegate to my own one to so that i
> > get my own representation of the date value.
> > This works well for the items in the drop-down list, but not for the one
> > in the selected field.
> > 
> > Where i have to set the delegate to get my representation of the date in
> > the selected field ?
> 
> It turns out it's a terrible ordeal.
> 
> The text on the combo box when not opened is not painted by a delegate.
> It kinda should be but that's too late to change now.
> 
> This usually leaves you with the option of changing the style or
> reimplementing paintEvent.
> 
> The former is usually cleaner but in this case I think I would go for
> the latter for this reason.
> 
> The style option passed to the style for painting the text converts the
> date into a string using QVariant::toString() which uses the rather
> illusive under-the-hood methods of QVariant for its conversion.
> 
> It does turn out that you can find the QDate using the following
> approach:
> 
> QVariant foo = styleOption->currentText;
> QDate date = foo.toDate();
> 
> but that's kinda nasty.
> 
> Moreover the style is not passed a pointer to the combobox itself so
> you'd have to hack horribly to get a hold of the actual model to find
> the real value.
> 
> That being said the paintEvent of QComboBox is rather nice and short and
> the parts of it that you don't want to change can easily be changed so I
> would recommend this method.
> 
> I did throw together an example taking the first approach but I would
> rather do something like this:
> 
> class MyCombo : ...
> {
>     void paintEvent(...)
>     {
>         QStylePainter painter(this);
>         painter.setPen(palette().color(QPalette::Text));
> 
>         // draw the combobox frame, focusrect and selected etc.
>         QStyleOptionComboBox opt;
>         initStyleOption(&opt);
>         /* All other lines are copied from qcombobox.cpp
> 
>         inside here you could do something along the lines of:
> 
>         opt.currentText =
> myConversionOfDateToString(currentIndex().data().toDate());
> 
>         */
> 
>         painter.drawComplexControl(QStyle::CC_ComboBox, opt);
> 
>         // draw the icon and text
>         painter.drawControl(QStyle::CE_ComboBoxLabel, opt);
>     }
> };
> 
> I've attached the example I did write.

Thanks for your example. I will give it a try.

In meanwhile i created a bug entry:
  http://bugreports.qt.nokia.com/browse/QTBUG-12360

I am currently working with Qt 4.6.2. But i haven't checked whether this issue 
have been fixed with 4.6.3 or the upcoming 4.7.

kind regards
  Petric