如何在 Linux 桌面中获取与文件关联的图标、MIME 类型和应用程序？

Question

Using C++ on the Linux desktop, what is the best way to get the icon, the document description and the application "associated" with an arbitrary file/file path?

I'd like to use the most "canonical" way to find icons, mime-type/file type descriptions and associated applications on both KDE and gnome and I'd like to avoid any "shelling out" to the command line and "low-level" routines as well as avoiding re-inventing the wheel myself (no parsing the mime-types file and such).

Edits and Notes:

Hey, I originally asked this question about the QT file info object and the answer that "there is no clear answer" seems to be correct as far as it goes. BUT this is such a screwed-up situation that I am opening the question looking for more information.

I don't care about QT in particular any more, I'm just looking for the most cannonical way to find the mime type via C++/c function calls on both KDE and gnome (especially Gnome, since that's where things confuse me most). I want to be able show icons and descriptions matching Nautilus in Gnome and Konquerer/whatever on KDE as well as opening files appropriately, etc.

I suppose it's OK that I get this separately for KDE and Gnome. The big question is what's the most common/best/cannonical way to get all this information for the Linux desktop? Gnome documentation is especially opaque. gnome-vsf has mime routines but it's deprecated and I can't find a mime routine for GIO/GFS, gnome-vsf's replacement. There's a vague implication that one should use the open desktop applications but which one to use is obscure. And where does libmagic and xdg fit in?

Pointers to an essay summarizing the issues gladly accepted. Again, I know the three line answer is "no such animal" but I'm looking for the long answer.

Answer 1

Here is an example of using GLib/GIO to get the information you want.

#include <gio/gio.h>
#include <stdio.h>

int
main (int argc, char **argv)
{
    g_thread_init (NULL);
    g_type_init ();

    if (argc < 2)
        return -1;

    GError *error;
    GFile *file = g_file_new_for_path (argv[1]);
    GFileInfo *file_info = g_file_query_info (file,
                                              "standard::*",
                                              0,
                                              NULL,
                                              &error);

    const char *content_type = g_file_info_get_content_type (file_info);
    char *desc = g_content_type_get_description (content_type);
    GAppInfo *app_info = g_app_info_get_default_for_type (
                                  content_type,
                                  FALSE);

    /* you'd have to use g_loadable_icon_load to get the actual icon */
    GIcon *icon = g_file_info_get_icon (file_info);

    printf ("File: %s\nDescription: %s\nDefault Application: %s\n",
            argv[1],
            desc,
            g_app_info_get_executable (app_info));

    return 0;
}

Answer 2

You can use the tools available from xdg for that, in particular xdg-mime query .

To find out the filetype of eg a file index.html you would

$ xdg-mime query filetype index.html

This will return the mimetype. To query what application is associated with that mimetye use eg

$ xdg-mime query default text/html

This returns epiphany.desktop here, ie $APPNAME.desktop , so it is easy to get the application name from it. If you would just want to open the file in the default app you could of course just run

$ xdg-open index.html

which would fire up epiphany.

Query functions for icon resources do not seem to be available in xdg-utils , but you could write a small python script using pyxdg that offers tons of additional functionality, too.

For C bindings you will probably need to have a look into the portland code linked on the xdg page.

EDIT:

Concerning libmagic and friends, you will need to decide on your preferences: While libmagic seems to be more complete (and accurate) in terms of coverage for filetypes, it does not care at all about default applications or icons. It also does not provide you with tools to install extra mimetypes.

Answer 3

In Qt >= 4.6, there is a new function for X11 systems

QIcon QIcon::fromTheme ( const QString & name, const QIcon & fallback = QIcon() ) [static]

You can use this function. Documentation here / (Qt 5)

Answer 4

Neither QFileIconProvider nor QFileInfo will do anything with the OS mime database. To access icons associated with different mime types, you will have to use functions of the underlying desktop environment. In Qt there is (yet) no canonical way.

Consider you can have a different icon in Gnome, in KDE and in Windows. So for instance, in KDE you would use KMimeType .

Answer 5

I just found KFileItem . This class gives you everything you for icons, mime types and related things in KDE. I'm sure that there's an equivalent in gnome but this gives access at the same level as a QT application works.

Answer 6

You may want to use the system's "/etc/mime.types" file. It is also a good idea to maintain your program's copy of a MIME type file. That way, you are not dependent on the system, but at the same time you need to keep it fairly exhaustive. Not sure about Icons.

Answer 7

Maybe take a look at this code: http://ftp.devil-linux.org/pub/devel/sources/1.2/file-4.23.tar.gz

This is the standard file util found on most Linux/Unix distributions. You will get the MIME-type and some more information.

I think both Gnome and KDE have their own ways to determine this and also to set the icon and the standard application for it.

Anyway, that file-tool is probably the best way to get the mime type and the document description. And in some cases even some details about the content.

This will get you the mime-type. That is what you need anyway to know how you can open the file. These are seperated steps. file doesn't say you about the icon nor the application to open the file with.

Answer 8

About 8 years late, but still useful.

To get the associated applications in KDE you can do what Joe suggested (using KFileItem ). However, that requires inclusion of a lot of libraries. The code below requires less.

#include <QCoreApplication>
#include <QMimeDatabase>
#include <QDebug>

#include <KMimeTypeTrader>

int main(int argc, char *argv[])
{
  QCoreApplication a(argc, argv);

  if (argc < 2)
  {
    qDebug() << "missing argument <filename>";
    return 1;
  }
  QMimeDatabase mimeDb;
  QMimeType     mimeType = mimeDb.mimeTypeForFile(QString::fromLocal8Bit(argv[1]));

  KService::List services = KMimeTypeTrader::self()->query(
      mimeType.name(),QStringLiteral("Application"));

  foreach(const QExplicitlySharedDataPointer<KService>& svc, services)
  {
    qDebug() << "service: " << svc->name();
    qDebug() << "exec: " << svc->exec();
  }
}

To compile the code add QT += KService KCoreAddons to your qmake .pro file.

Links to KMimeTypeTrader & KService documentation:

• https://api.kde.org/frameworks/kservice/html/classKService.html
• https://api.kde.org/frameworks/kservice/html/classKMimeTypeTrader.html

Answer 9

Copy/Paste of the nice example above (using GLib/Gio) just added proper release of allocated memory as per documentation. I tried to just edit the existing answer but it kept saying the edit queue was full :(

#include <gio/gio.h>
#include <stdio.h>

int
main (int argc, char **argv)
{
    g_thread_init (NULL);
    g_type_init ();

    if (argc < 2)
        return -1;

    g_autoptr(GError) error;
    GFile* file = g_file_new_for_path (argv[1]);
    GFileInfo* file_info = g_file_query_info (file,
                                              "standard::*",
                                              G_FILE_QUERY_INFO_NONE,
                                              NULL,
                                              &error);

    const char* content_type = g_file_info_get_content_type (file_info);
    g_autofree gchar* desc = g_content_type_get_description (content_type);
    GAppInfo* app_info = g_app_info_get_default_for_type (
                                  content_type,
                                  FALSE);

    /* you'd have to use g_loadable_icon_load to get the actual icon */
    GIcon* icon = g_file_info_get_icon (file_info);

    printf ("File: %s\nDescription: %s\nDefault Application: %s\n",
            argv[1],
            desc,
            g_app_info_get_executable (app_info));

    g_object_unref(file_info);
    g_object_unref(file);
    return 0;
}