[Qt-interest] Calculating text size in QLineEdit

[Matthias Paul]

-------- Original-Nachricht --------
> Datum: Tue, 8 Mar 2011 11:23:32 +0100
> Von: "Andre Somers" <andre at familiesomers.nl>
> An: qt-interest at trolltech.com
> Betreff: Re: [Qt-interest] Calculating text size in QLineEdit

> Hi,
> 
> Op Di, 8 maart, 2011 11:10 am, schreef Matthias Paul:
> >
> > -------- Original-Nachricht --------
> >> Datum: Tue, 8 Mar 2011 10:20:23 +0100
> >> Von: "Andre Somers" <andre at familiesomers.nl>
> >> An: "\'qt-interest at trolltech.com\'" <qt-interest at trolltech.com>
> >> Betreff: Re: [Qt-interest] Calculating text size in QLineEdit
> >
> >> Op Di, 8 maart, 2011 10:06 am, schreef Matthias Paul:
> >> > Hello!
> >> >
> >> > I created a QLineEdit subclass, which automatically displays a
> >> truncated
> >> > text if the original text is too long for the widget's size, so that
> >> > there's no need to scroll for the user. Instead a tooltip with full
> >> text
> >> > is displayed.
> >> >
> >> > QFontMetrics calculates the size required for the displayed text
> based
> >> on
> >> > QWidget's size() (provided by ResizeEvent). Still, I cannot figure
> out
> >> how
> >> > to get the the text label size _minus_ widget's borders and margins.
> >> Guess
> >> > I have to use QStyle somehow, so can someone give me a hint please?
> >>
> >> Perhaps you can use QStyle::subElementRect, using
> >> QStyle::SE_LineEditContents for the element argument, and a style
> option
> >> initialized with your line edit widget as the style option? That should
> >> give you the rect that is available to draw the text.
> >>
> >> André
> >>
> >
> > Hello André!
> >
> > Thank you for your reply!
> >
> > The subelementRect() always returns an invalid QRect, although the
> > QLineEdit is displayed and has content in it.
> >
> > That's what I tried: (typos included)
> > --------------------------------------------------
> > void
> > TruncatedLineEdit::resizeEvent(
> >     QResizeEvent * resizeEvent) {
> >
> >   QLineEdit::resizeEvent(resizeEvent);
> >
> >   qDebug() << "QWidget's size (by event):" << resizeEvent->size();
> >   QStyleOption option;
> >   option.initFrom(this);
> >   qDebug() << "QWidget's content rect (by style):"
> >            << this->style()->subElementRect(
> >                   QStyle::SE_LineEditContents,
> >                   &option,
> >                   this);
> >   // do smth with size information
> > }
> > --------------------------------------------------
> >
> > The output is:
> > --------------------------------------------------
> > QWidget's size (by event): QSize(246, 22)
> > QWidget's content rect (by style): QRect(0,0 0x0)
> > --------------------------------------------------
> >
> >
> > Is it because QLineEdit has no user-style set to it? QLineEdit has been
> > set with usual calls like setFont(), setReadOnly() and setObjectName().
> 
> I would have expected your code to work. I don't know why it doesn't.
> Sorry! Perhaps you can check QLineEdit's sources to find out how QLineEdit
> itself determines the rect to draw the text in?
> 
> André
> 

Thanks again for your help.

I took your advice and read into qlineedit.cpp, method sizeHint().
The calculation for width (of edit content, right?) simply resolves to:
-----------------------------------------------------------
[... some code ...]

int w = fm.width(QLatin1Char('x')) * 17 + 2*d->horizontalMargin
        + d->leftTextMargin + d->rightTextMargin
        + d->leftmargin + d->rightmargin;
QStyleOptionFrameV2 opt;
initstyleOption(&opt);
return (style()->sizeFromContents(QStyle::CT_LineEdit, &opt, QSize(w,h).
                                  expandedTo(QApplication::globalStruct()), this);
-----------------------------------------------------------

Clear to me. Still I'd like to know two things:

1. Q_D macro accesses the "private impl" pointer. In my subclass I cannot access this macro, nor am I allowed to do so, right? So is there another way to access members "leftTextMargin", "rightTextMargin" and so on from pimpl pointer?

2. Is QStyleOptionFrameV2 the default frame type for a QLineEdit? It seems to be not safe to use this class definition, as it may change in future Qt releases.
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