Development/Tutorials/KCM HowTo
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Introduction
This howto describes how to write KConfig Modules (KCMs from now on). These KCM can appear in System Settings or in the configuration dialog of individual applications.
A KCM is made of two elements:
- A shared library
- A desktop file
Implementing a KCM is done by:
- Subclassing the KCModule class. In this documentation we assume the class inheriting from KCModule is named FooKcm.
- Exporting the module so that System Settings or kcmshell5 can find it.
The prefered way to export the module is through KPluginFactory. Here is how to do it:
#include <KPluginFactory>
K_PLUGIN_FACTORY(FooKcmFactory, registerPlugin<FooKcm>();)
K_EXPORT_PLUGIN(FooKcmFactory("kcm_foo" /* kcm name */, "kcm_foo" /* catalog name */))
If you get errors, make sure the constructor signature of your derived class matches with the signature of KCModule constructor (the QVariantList argument matters).
If the name of your module is "foo", the name of the library should be "kcm_foo.so". It should be installed into $KDEDIR/lib/kde4.
Exporting more than one module
If you need to export more than one module per library, you have to declare them another way: you must create C functions named "create_${kcm_name}". For example if your module exposes two KCMs named Foo1 and Foo2, the "create_" functions would look like this:
extern "C"
{
KCModule *create_foo1(QWidget *parent, const char *name)
{
return new Foo1Kcm(parent, name);
};
KCModule *create_foo2(QWidget *parent, const char *name)
{
return new Foo2Kcm(parent, name);
};
}
Additionally, you will need to add "X-KDE-FactoryName" keys to your desktop file. (see below)
Initializing on startup
It is possible to get code from the KCM to be run at startup by kcminit.
To do so you must declare a function named "kcminit_${module}", like this:
extern "C"
{
KDEEXPORT void kcminit_foo()
{
// Do initialization here
};
}
You must also add a "X-KDE-Init-Symbol" key to your desktop file. (see below)
The desktop file
To declare a KCModule's existence a desktop file must be installed in the proper place.
Desktop files are defined in the desktop file specification.
Mandatory keys
A KCM desktop file must contains the following keys:
- Type
Should be "Service".
- X-KDE-ServiceTypes
Should be "KCModule" for most KCM. If you want to use the kcminit feature it should be "KCModule,KCModuleInit".
- Icon
Specifies the icon for the module.
- Exec
Should be "kcmshell5 foo".
- Name
This will be used by System Settings as your KCM label.
- Comment
This text shows up in the title area in System Settings. If the module is not grouped with other modules it will also be used as a tooltip in the KCM list view.
- Categories
Should contain at least "Qt;KDE;X-KDE-settings-system;".
- X-KDE-ParentApp
Set this to "kcontrol" if you want your KCM to show up in System Settings.
The application you put in this key determines in what situations your KCM will show. It is crucial to select a correct ParentApp, otherwise the KCM will show up in unnecessary places.
- X-KDE-System-Settings-Parent-Category
Defines where the KCM will appear in System Settings.
Possible values at the time of this writing are:
- settings-lost-and-found
- settings-hardware
- settings-network-and-connectivity
- settings-system-administration
- settings-application-appearance-and-behavior
- settings-workspace-appearance-and-behavior
You can get a list of possible categories with this command, which lists all toplevel categories:
ktraderclient --servicetype SystemSettingsCategory --constraint "[X-KDE-System-Settings-Parent-Category] == ''" | grep DesktopEntryName
Just do not use the "settings-lost-and-found" entry.
- X-KDE-Keywords
A comma-separated list containing words the search functionality should trigger on.
- X-KDE-Library
This is the name of the library, without the "kcm_" prefix. In our example, it should be "foo".
Optional keys
Additionally the KCM desktop file may contains the following keys:
- X-KDE-FactoryName
This entry can be used to set the name of the factory function in the library. If you only have one KCModule in a library this key is not needed. If you have several KCMs in one library you will need a desktop file for each KCM.
For example, if you have a library named: kcm_frog.so with two modules, named "kermit" and "quak", kcm_kermit.desktop would contain:
X-KDE-Library=frog
X-KDE-FactoryName=kermit
and "kcm_quak.desktop" would contain:
X-KDE-Library=frog
X-KDE-FactoryName=quak
The module loader would then call the "create_kermit" and "create_quak" functions respectively.
- X-KDE-Init-Symbol
If the module has to perform some action at system startup, use this entry to build the name of a function to call. if X-KDE-Init-Symbol is "bell", for example, the function "kcminit_bell" is called in the library indicated by X-KDE-Library.
- NoDisplay
If this is set to true the module will not show up in System Settings or when viewed with kcmshell5. This is useful when you need to do something at startup using X-KDE-Init but don't want the module to show up in System Settings.
You can also make the value of this key depend on the output of a program, using the "[$e]" key suffix. For example:
Hidden[$e]=$(if test -e /dev/js*; then echo "false"; else echo "true"; fi)
This example executes the given code in a shell and uses the stdout output for the Hidden value (so it's either Hidden=true or Hidden=false).
Example CMakeLists.txt
Here is a minimal CMakeLists.txt which builds and installs the shared library and the desktop files at the right places:
find_package(KDE4 REQUIRED)
include(KDE4Defaults)
include(MacroLibrary)
set(FOO_SRCS
foo.cpp
# Other sources go there
)
kde4_add_plugin(kcm_foo ${FOO_SRCS})
target_link_libraries(kcm_foo
${KDE4_KDEUI_LIBS}
# Other necessary libraries go there
)
install(TARGETS kcm_foo
DESTINATION ${PLUGIN_INSTALL_DIR}
)
install(FILES kcm_foo.desktop
DESTINATION ${SERVICES_INSTALL_DIR}
)
Please note that your library name should only contain letters (upper and lowercase), numbers and underscores ("[A-Z][a-z][0-9]_"), because this name will be used internally as a dbus object. So "kcm_foo" is fine while "kcm-foo" is not.
What else do I need?
There are a number of additional things for convenience.
kcmshell5
You can run one or several modules independently with "kcmshell5 [module_name]". For example, to get the font and the desktop color settings, use "kcmshell5 fonts colors".
To get a list of the available modules, use "kcmshell5 --list".
KCMultiDialog
Sometimes, you may want to reuse your KCModule inside an application. There are two ways to accomplish this:
The first option is to simply fork and call "kcmshell5 foo".
The second option is to use KCMultiDialog. This is a simple dialog which can show an arbitrary number of modules in a normal KDialog. This approach gives you finer control than starting kcmshell5 in a separate process.
Since your module is a simple library, you can just link to it anyway.
KCModuleContainer
The class KCModuleContainer allows great flexibility to handle modules. The API docs explains its usage the best.
Debugging your module
You can attach gdb, valgrind or whatever to "kcmshell5 [yourmodule]" to track down leaks or crashes. If you need to trace it down inside System Settings, make sure you pass --nofork to System Settings on startup.
You really want to use kcmshell5 for debugging as long as your debugging does not involve debugging bad interaction with the System Settings framework itself.
About this howto
This howto has been imported from http://websvn.kde.org/trunk/www/sites/developer/documentation/other/kcm_howto.html?view=markup and refreshed for KDE4 by Aurélien Gâteau <[email protected]>.
Original copyright header:
Copyright (C) 2003 Daniel Molkentin <[email protected]> Copyright (C) 2004 Frans Englich <[email protected]> Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".