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

Revision as of 14:38, 22 July 2009

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 (libapplet.c) needs two functions. These functions are defined in

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

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 might be unloaded when execute returns, so no g_timeouts, gconf_notifys or such should be left when done. Gtk or osso initialization is not needed, as they are already done at this point.

#include <hildon-cp-plugin/hildon-cp-plugin-interface.h>
#include <gtk/gtk.h>
osso_return_t execute(osso_context_t *osso, gpointer data, gboolean user_activated)
{
	GtkWidget *dialog;
	gint response;
	/* Create dialog with OK and Cancel buttons. Leave the separator out,
	 * as we do not have any content. */
	dialog = gtk_dialog_new_with_buttons(
		"Hello control panel",
		GTK_WINDOW(data),
		GTK_DIALOG_MODAL | 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 = gtk_dialog_run(GTK_DIALOG(dialog));
	if (response == 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;
}

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, this should be used.

osso_return_t save_state(osso_context_t *osso, gpointer data)
{
	/* ... save state ... */
	return OSSO_OK;
}

Building applet

To use the applet, it needs to be built into a dynamic library aka shared object. This can be accomplished by giving flag -shared to gcc.

[sbox-FREMANTLE_X86: ~] > gcc -shared `pkg-config gtk+-2.0 libosso --libs --cflags` libapplet.c 
-o libapplet.so

The binary produced by gcc should be installed to path specified in hildon-control-panel pkg-config entry. This path can be obtained with pkg-config hildon-control-panel -variable=pluginlibdir. By default this 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.

[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

The desktop file must be installed 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, this is /usr/share/applications/hildon-control-panel.