Documentation/Maemo 5 Developer Guide/Application Development/Writing Control Panel Applets

2009-10-03T07:38:16Z

88.113.0.16: /* Building applet */

= Writing control panel applets =
The control panel is designed to be extendable, and items can be added to it with dynamic libraries with certain functions and desktop files describing the library.

== Functions ==
A control panel applet ([https://garage.maemo.org/svn/maemoexamples/trunk/maemo-examples/libapplet.c libapplet.c]) needs two functions. These functions are defined in the following:

<tt>'''<nowiki>#include</nowiki>''' <hildon-cp-plugin/hildon-cp-plugin-interface.h></tt>

The first and more important one, execute, is called when the applet is activated from Control Panel. Usually this function creates a dialog and waits until it is done. Any dialog created should be modal to the window in parameter.
N.B. The library can be unloaded when execute returns, so no g_timeouts, gconf_notifys or such must be left when done. Gtk or osso initialization is not needed, because they are already done at this point.

<tt>'''<nowiki>#include</nowiki>''' <hildon-cp-plugin/hildon-cp-plugin-interface.h>
'''<nowiki>#include</nowiki>''' <gtk/gtk.h>
osso_return_t '''execute'''(osso_context_t <nowiki>*</nowiki>osso, gpointer data, gboolean user_activated)
{
GtkWidget <nowiki>*</nowiki>dialog<nowiki>;</nowiki>
gint response<nowiki>;</nowiki>
''/* Create dialog with OK and Cancel buttons. Leave the separator out,''
'' * as we do not have any content. */''
dialog <nowiki>=</nowiki> '''gtk_dialog_new_with_buttons'''(
"Hello control panel",
'''GTK_WINDOW'''(data),
GTK_DIALOG_MODAL <nowiki>|</nowiki> GTK_DIALOG_NO_SEPARATOR,
GTK_STOCK_OK,
GTK_RESPONSE_OK,
GTK_STOCK_CANCEL,
GTK_RESPONSE_CANCEL,
NULL);
''/* ... add something to the dialog ... */''
'''if''' (!user_activated)
{
''/* ... load state ... */''
}
''/* Wait until user finishes the dialog. */''
response <nowiki>=</nowiki> '''gtk_dialog_run'''('''GTK_DIALOG'''(dialog));
'''if''' (response <nowiki>==</nowiki> GTK_RESPONSE_OK)
{
''/* ... do something with the dialog stuff ... */''
}
''/* Free the dialog (and it's children) */''
'''gtk_widget_destroy'''('''GTK_WIDGET'''(dialog));
'''return''' OSSO_OK<nowiki>;</nowiki>
}
</tt>

The other function is called save_state. It is called when application using the applet is saving state. Usually this does nothing, but if support for state saving is needed, use it.

<tt>osso_return_t '''save_state'''(osso_context_t <nowiki>*</nowiki>osso, gpointer data)
{
''/* ... save state ... */''
'''return''' OSSO_OK<nowiki>;</nowiki>
}
</tt>

== Building applet ==
To use the applet, build it into a dynamic library aka shared object by giving flag -shared to gcc.

<div class="graybox">
[sbox-FREMANTLE_X86: ~] > gcc -shared `pkg-config gtk+-2.0 hildon-control-panel libosso --libs --cflags` libapplet.c
-o libapplet.so
</div>

Install the binary produced by gcc to a path specified in hildon-control-panel pkg-config entry. You can obtain this path with pkg-config hildon-control-panel --variable=pluginlibdir. By default it is /usr/lib/hildon-control-panel.

==The .desktop file ==
Any control panel applet needs a desktop file describing it. The file contains metadata like name, icon name and library of the applet. The applet desktop file is much like the desktop file for any other application.

Here is an example desktop file (applet.desktop) for the applet created above:

<div class="graybox">
[Desktop Entry]
Encoding=UTF-8
Version=1.0
Name=Control Panel Hello World
Comment=A control panel example applet
Type=HildonControlPanelPlugin
Icon=qgn_list_cp_isetup
X-control-panel-plugin=libapplet.so
Categories=general

</div>

Install the desktop file to directory specified in pkg-config file for hildon-control-panel. This directory can be obtained by ''`pkg-config hildon-control-panel --variable=plugindesktopentrydir`''. By default, it is /usr/share/applications/hildon-control-panel.

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Documentation/Maemo 5 Developer Guide/Application Development/Writing Control Panel Applets