Desktop file

For your application to show up in menus, or to be offered for MIME types in file managers, it needs a .desktop file like this:

[Desktop Entry]
Type=Application
Exec=your-app %u
TryExec=your-app
MimeType=application/x-your-mime-type;
Icon=some-icon
X-DocPath=yourapp/index.html
Terminal=false
Name=Your App
GenericName=Some Generic Name
Comment=Short Description Of Your App
Categories=Qt;KDE;

The Desktop Entry Specification describes all the keys.

Name, Type and Exec are essential. Name is the application's name. Type=Application makes it a program that appears in menus. Exec is the command that starts it.

TryExec names a command used to check that the application is actually installed: if it can't be found in the $PATH (typically when a user wrote their own .desktop file and later uninstalled the application), the entry isn't shown in menus.

Icon is either the path of an icon shipped with your application or the name of an icon available in the system's icon theme. Terminal=false says the application doesn't need to run in a terminal, which is usual for graphical applications.

X-DocPath is the path of the application's handbook, used to open its documentation (for example by the Help menu).

Choose good Categories so users find your application. Without them, it ends up in the menu's "Lost & Found" category. Categories are separated by semicolons (;).

MimeType lists the MIME types your application handles, which decides whether it is offered to open a file of that type. A plain text editor, for example, uses text/plain, so it appears under "Open With" for text files, and an email application uses x-scheme-handler/mailto to handle mailto: links. MIME types are separated by semicolons (;); the shared-mime-info repository has a comprehensive list of the MIME types used on Linux.

#Translations

The example has only English texts. To translate a key, add a [lang] suffix to it:

Name=Your Application
Name[fr]=Ton application
...
GenericName=Some Generic Name
GenericName[fr]=Un nom générique

If your project's translations are managed by a translation team, don't translate the .desktop file yourself. KDE, for example, has a bot called Scripty that extracts the texts of .desktop files into .po (gettext) files for its translators, and writes the translations back into the file afterwards.

#Installing the .desktop file

In your CMakeLists.txt, install the file with ECM's KDEInstallDirs:

install(FILES org.example.my-app.desktop DESTINATION ${KDE_INSTALL_APPDIR})

Name the file after your application's reverse-domain ID, as here (org.example.my-app.desktop), and give the same name to QGuiApplication::setDesktopFileName() or KAboutData, so that the desktop (task manager, notifications) can match your windows to the file.