[Qt-interest] Force file extension with QFileDialog::getSaveFileName?

[Eric Clark]

> -----Original Message-----
> From: qt-interest-bounces+eclark=ara.com at qt.nokia.com [mailto:qt-
> interest-bounces+eclark=ara.com at qt.nokia.com] On Behalf Of Constantin
> Makshin
> Sent: Wednesday, June 22, 2011 12:45 PM
> To: Qt Interest
> Subject: Re: [Qt-interest] Force file extension with
> QFileDialog::getSaveFileName?
> 
> I had read the thread before posting my message.
> 
> Initially David said he tried this:
> 
> QFileDialog dialog(this);
> dialog.setFilter(".png .bmp");
> dialog.setDefaultSuffix(".png");
> cout << dialog.getSaveFileName().toStdString();
> 
> and had no luck. Then (exactly in the message I answered to) he provided a
> link to the page with this:
> 
> // For some reason this doesn't work?
> QFileDialog dialog(this);
> //dialog.setFilter(".png .bmp");
> dialog.setNameFilter("*.png;;*.bmp");
> dialog.setDefaultSuffix("png");
> QString fileName = dialog.getSaveFileName();
> 
> Yes, in both cases he used the setDefaultSuffix() function. But then he called
> getSaveFileName() and was (or, at least, it seemed like he was) surprised
> that didn't work. But we all know getSaveFileName() will remain static (and
> thus unaware of any customizations made by setDefaultSuffix() and other
> non-static functions) no matter how one calls it — as
> QFileDialog::getSaveFileName() or as dialog.getSaveFileName().
> 
> And again, I apologize if any of my messages insulted anyone.

That was my fault. I did not pay close enough attention to the code that he wrote. I quickly glanced over it and did not realize he was still calling the static function.

Personally, I have always thought that the syntax for static function calls was a little awkward when you are allowed to call them from an instance. It can be very confusing to allow both forms of calling the static function:

dialog.getSaveFileName(...)

or 

QFileDialog::getSaveFileName(...)

But, as you pointed out, this is common among just about every language. Maybe David was unaware of this and thus your point was a good one. My apologies for responding the way I did.

Eric

> 
> On Wednesday, June 22, 2011 09:13:19 PM Eric Clark wrote:
> >
> > > -----Original Message-----
> > > From: qt-interest-bounces+eclark=ara.com at qt.nokia.com [mailto:qt-
> > > interest-bounces+eclark=ara.com at qt.nokia.com] On Behalf Of
> > > interest-bounces+Constantin
> > > Makshin
> > > Sent: Wednesday, June 22, 2011 12:03 PM
> > > To: Qt Interest
> > > Subject: Re: [Qt-interest] Force file extension with
> > > QFileDialog::getSaveFileName?
> > >
> > > I don't want to insult anyone, but there's a problem with the way
> > > those who expect setDefaultSuffix() to affect getSaveFileName()
> > > think. There's simply no logic in that — getSaveFileName() is a
> > > *static* function, so there's no way it can access non-static object
> > > members (just because static functions don't have any object to work
> > > with) set by setDefaultSuffix(). It's not specific to Qt or even C++, it's the
> way static functions work in any programming language.
> > > I apologize if that sounds too rude.
> >
> > It is only rude because you did not pay attention to everything that was
> said in the thread. Both David and I are fully aware of the fact that the
> function is only to be used with an instance of the dialog and not the static
> functions. Please pay attention to the whole thread next time before you go
> trying to explain how we don’t understand static functions in any language.
> >
> > David made an attempt to use the setDefaultSuffix function with an
> instance of the QFileDialog class, not the static function getSaveFileName,
> and it still does not do what the documentation says it should. So, if you want
> to help please don’t just show up in the middle of it without knowledge of
> everything that was going on. Or at least read the whole thread before you
> respond.
> >
> > Thanks,
> > Eric
> >
> > >
> > > As for the question about default extension in getSaveFileName(), in
> > > my application I call it this way:
> > >
> > > QString fileName = QFileDialog::getSaveFileName(this, tr("Save
> > > Technique"), m_technique->fileName(), MainWindow::tr("Production
> > > Techniques XML (*.ptx *.ptxml);;All Files (*.*)"));
> > >
> > > And if the user doesn't change the filter and doesn't explicitly
> > > specify any file extension, "ptx" is added automatically. I.e. if
> > > the user types "somefile" into the file name box, fileName will be
> > > equal to "somefile.ptx". And this works correctly at least on
> > > Windows and GNU/Linux with KDE (once I asked a friend to test the
> > > application on Mac OS X and didn't get any complaints related to default
> extension, but there was no thorough testing on that platform).
> > >
> > > On Wednesday, June 22, 2011 03:35:17 PM David Doria wrote:
> > > > > Guys, nothing is wrong with the docu ;) The setDefaultSuffix
> > > > > method only
> > > has an impact on a QFileDialog *instance*, but the OP was calling
> > > the *static* method which triggers the creation of a *native* file
> > > dialog, which might or might not add the suffix by itself already.
> > > On Mac the extension is added depending on the current filter, if
> > > the filter happens to be unique (e.g. "PNG (*.png)" as opposed to
> > > "Images (*.png, *.jpg, *.bmp)"), on Windows not quite sure,
> > > KDE/Gnome native file dialogs apparently don't auto-suffix your
> filename.
> > > > >
> > > > > That said, I am not even sure whether setDefaultSuffix() has an
> > > > > impact on
> > > the *native* file dialog - might be that Qt expands the filename
> > > accordingly in "post production" (after the native dialog has returned).
> > > > >
> > > > > It works for sure with the Qt file dialog, but that one has
> > > > > several
> > > limitations and disadvantages. One being that the suffix cannot be
> > > auto- applied depending on the selected filter (if you want to save
> > > under multiple file formats, for instance, and the filter would
> > > specify the format such as "Template" or "Document"). Only one
> > > suffix can be supplied with setAutoSuffix.
> > > > >
> > > > > Cheers, Oliver
> > > >
> > > > Hi Oliver, they set me straight on making an instance of the
> > > > dialog right away :)
> > > >
> > > > I'm not sure I follow the rest of what you said? Would you mind
> > > > taking a look? The example has commented out an attempt with a
> > > > static method (which apparently everyone agrees should not work),
> > > > another commented section shows the attempt with setDefaultSuffix,
> > > > and the uncommented section shows the manual method:
> > > >
> > > >
> > >
> http://programmingexamples.net/index.php?title=Qt/Widgets/FileDialog
> > > De
> > > > faultSuffix
> > > >
> > > > Again the documentation says "This property specifies a string
> > > > that will be added to the filename if it has no suffix already."
> > > > and I'm just not seeing that happen.
> > > >
> > > > Thanks,
> > > >
> > > > David