Default Program | File Association

[David Faure]

On Tuesday 29 January 2008, Stanislav Brabec wrote:
> 
> It is a very complex task to create correct defaults.list using the
> current format. For example (GNOME), you have to do manually:
> 
> - Fill eog.desktop for all image MIME types mentioned in eog.desktop
> 
> - Find all MIME types not mentioned in eog.desktop but opened by another
>   GTK/GNOME viewer and fill this viewer to these MIME types.
> 
> - Find all MIME types not opened by any of above and fill generic image
>   viewer there.
> 
> It is even a fragile task - if any of the image viewers is removed,
> there is no way to find "second best fit" and application has to choose
> randomly.

The above is exactly why applications should *NOT* touch defaults.list files IMHO.
Those files exist to save the user's preference, possibly a sysadmin preference, but only that.

Applications should simply install a .desktop file that describes them.
In order for the default order of applications (i.e. without user configuration available)
to be non-random, we (in KDE) use a InitialPreference field in the .desktop file,
and the default application for a mimetype is the one with the highest initial preference number.

You might say: but then every application will use 4 billion or more in that field,
but I have actually never seen that happen (and this would be equivalent with app installers
modifying defaults.list anyway, so no difference there).
In practice people use reasonable numbers (between 1 and 10) and this feature 
allows KDE releases to come out with a predefined application order, which allows to 
make sure that the order isn't stupid: for instance, even though karbon can sort 
of import postscript files (so karbon.desktop mentions application/postscript), kghostview 
was a much better default application for viewing postscript; so we simply made 
sure that kghostview had a higher InitialPreference than karbon.
This example also shows that InitialPreference really has to be per-mimetype supported
in a given desktop file, not just for the whole desktop file (although that's good enough
in 95% of the cases of course). Hence my suggestion in a previous mail, for a new 
section in .desktop files which defines per-mimetype initial preference:
[InitialPreferences]
text/plain=2
application/postscript=6

(this makes this application preferred over another app that has <6 for application/postscript,
but if a third application handles text better then it will be used instead of this one).

I would really like this clean solution (cleaner than kde's current hack for
per-mimetype preference numbers) to be added to the desktop entry standard.

-- 
David Faure, faure at kde.org, sponsored by Trolltech to work on KDE,
Konqueror (http://www.konqueror.org), and KOffice (http://www.koffice.org).