FedericoMena-Quinterofederico@ximian.comMigrating from old menu and toolbar systems to GtkAction
Prior to GTK+ 2.4, there were several APIs in use to create menus
and toolbars. GTK+ itself included #GtkItemFactory, which was
historically used in the GIMP; libgnomeui provided the gnome-ui
set of macros; libbonoboui provided a complex mechanism to do menu
merging across embedded components. GTK+ 2.4 includes a system
for creating menus and toolbars, with merging of items, based
around the #GtkAction mechanism.
Actions and Action Groups
A #GtkAction represents an operation that the user can perform from
the menus and toolbars of an application. It is similar to "verbs"
in other menu systems. A #GtkAction has a name, which is its identifier,
and it can have several widgets that represent it in the user interface.
For example, an action for EditCopy can have a menu item
as well as a toolbar button associated to it. If there is nothing selected
in the document, the application can simply de-sensitize the
EditCopy action; this will cause both the menu
item and the toolbar button to be de-sensitized automatically.
Similarly, whenever the user selects the menu item or the
toolbar button associated to the EditCopy
action, the corresponding #GtkAction object will emit an
"activate" signal.
#GtkActionGroup is simply a group of #GtkAction objects. An
application may want to have several groups: one for global
actions such as "new document", "about", and "exit"; then one
group for each open document with actions specific to the
document, such as "cut", "copy", "paste", and "print".
Normal actions are simply commands, such as
FileSave or EditCopy.
Toggle actions can be active or inactive, such as
FormatBold or ViewShowRulers.
Radio actions define a set of items for which one and only one
can be active at a time, for example, {
ViewHighQuality,
ViewNormalQuality,
ViewLowQuality }.
User Interface Manager Object
#GtkUIManager is an object that can construct menu and toolbar widgets
from an XML description. These widgets are in turn associated to
corresponding actions and action groups.
#GtkUIManager supports merging of menus and toolbars for applications
that have multiple components, each with separate sets of commands.
For example, a word processor that can embed images may want to have
toolbar buttons for Bold and Italic when the cursor is on a text
block, but Crop and Brightness/Contrast buttons when the cursor
is on an image. These actions, which change depending on the
state of the application, can be merged and de-merged from a
#GtkUIManager as appropriate.
Migrating from GnomeUIInfo
Prior to GTK+ 2.4, some applications used the GnomeUIInfo
mechanism from
<libgnomeui/gnome-app-helper.h> to
define their menus and toolbars. With it, a program decleres an
array of GnomeUIInfo structures, which
contain information for menu or toolbar items such as their
label, icon, and accelerator key. Then, one calls
gnome_app_fill_menu() or gnome_app_fill_toolbar(), or one of the
related functions, to create the appropriate widgets based on
these structures.
A downside of this API is that the same structures are used to
pass back pointers to the widgets that got created. This means
that the structures cannot simply be kept around if the program
requires multiple instances of the user interface (e.g. several
windows); each new invocation of gnome_app_fill_menu() would
overwrite the widget fields of the structures.
Another disadvantage is that there is no automatic way to
synchronize the state of related controls. If there are toolbar
toogle buttons for "Bold", "Italic", "Underline", and also
corresponding menu items under "Format/Bold", etc., one has to
synchronize their toggled states by hand whenever the user
selects any one of them.
Finally, there is no way to do menu and toolbar merging for
applications that require embedded components.
To convert an application that uses GnomeUIInfo into the new
GtkAction mechanism, you need to do several things:
Separate your existing GnomeUIInfo entries into normal
actions, toggle actions, and radio actions, and then create
a separate array of #GtkActionEntry structures
for each group. This will allow you to create the necessary
#GtkActionGroup objects. Note that this does not describe
the actual "shape" that your menus and toolbars will have;
it simply defines the set of commands that will appear in them.
Create an XML description of your menus and toolbars for use
with #GtkUIManager. This defines the actual shape of the menus
and toolbars.
Port the code that uses gnome-app and gnome-app-helper to
#GtkAction and #GtkUIManager.
If your GnomeUIInfo entries use GNOME_APP_PIXMAP_DATA or
GNOME_APP_PIXMAP_FILENAME for pixmaps, you have to create a
#GtkIconFactory, add it to the list of default factories, then
create a #GtkIconSet for each of your own icons. Add the sets to
the factory, and use the id in the #GtkActionEntry like a regular
GTK+ stock id.
GnomeUIInfo Example
The following code shows a declaration of a simple menu bar to
be used with gnome_app_fill_menu() or similar. The menu hierarchy i
looks like this:
FileOpen—ExitViewZoom InZoom Out—[ ] Full Screen—( ) High Quality( ) Normal Quality( ) Low Quality
static GnomeUIInfo file_menu_items[] = {
{ GNOME_APP_UI_ITEM, "_Open", "Open a file",
open_callback, NULL, NULL, GNOME_APP_PIXMAP_STOCK, GTK_STOCK_OPEN,
'o', GDK_CONTROL_MASK, NULL },
{ GNOME_APP_UI_SEPARATOR },
{ GNOME_APP_UI_ITEM, "E_xit", "Exit the program",
exit_callback, NULL, NULL, GNOME_APP_PIXMAP_STOCK, GTK_STOCK_QUIT,
'q', GDK_CONTROL_MASK, NULL},
{ GNOME_APP_UI_ENDOFINFO }
};
static GnomeUIInfo view_radio_items[] = {
{ GNOME_APP_UI_ITEM, "_High Quality", "Display images in high quality, slow mode",
high_quality_callback, NULL, NULL, GNOME_APP_PIXMAP_FILENAME, "high-quality.png",
0, 0, NULL },
{ GNOME_APP_UI_ITEM, "_Normal Quality", "Display images in normal quality",
normal_quality_callback, NULL, NULL, GNOME_APP_PIXMAP_FILENAME, "normal-quality.png",
0, 0, NULL },
{ GNOME_APP_UI_ITEM, "_Low Quality", "Display images in low quality, fast mode",
low_quality_callback, NULL, NULL, GNOME_APP_PIXMAP_FILENAME, "low-quality.png",
0, 0, NULL },
{ GNOME_APP_UI_ENDOFINFO }
};
static GnomeUIInfo view_menu_items[] = {
{ GNOME_APP_UI_ITEM, "Zoom _In", "Zoom into the image",
zoom_in_callback, NULL, NULL, GNOME_APP_PIXMAP_STOCK, GTK_STOCK_ZOOM_IN,
GDK_PLUS, 0, NULL },
{ GNOME_APP_UI_ITEM, "Zoom _Out", "Zoom away from the image",
zoom_out_callback, NULL, NULL, GNOME_APP_PIXMAP_STOCK, GTK_STOCK_ZOOM_OUT,
GDK_MINUS, 0, NULL },
{ GNOME_APP_UI_SEPARATOR },
{ GNOME_APP_UI_TOGGLEITEM, "_Full Screen", "Switch between full screen and windowed mode",
full_screen_callback, NULL, NULL, GNOME_APP_PIXMAP_NONE, NULL,
GDK_F11, 0, NULL },
{ GNOME_APP_UI_SEPARATOR },
{ GNOME_APP_UI_RADIOITEMS, NULL, NULL, view_radio_items },
{ GNOME_APP_UI_ENDOFINFO }
};
static GnomeUIInfo menubar[] = {
{ GNOME_APP_UI_SUBTREE, "_File", NULL, file_menu_items },
{ GNOME_APP_UI_SUBTREE, "_View", NULL, view_menu_items },
{ GNOME_APP_UI_ENDOFINFO }
}
<structname>GtkActionEntry</structname> Structures
The following code is the set of actions that are present in
the previous
example. Note that the toggle and radio entries are
separate from normal actions. Also, note that #GtkActionEntry
structures take key names in the format of gtk_accelerator_parse()
rather than key values plus modifiers; you will have to convert these
values by hand. For example, %GDK_F11 with no modifiers is equivalent
to a key name of "F11". Likewise, "o"
with %GDK_CONTROL_MASK is equivalent to "<ontrol>O".
/* Normal items */
static const GtkActionEntry entries[] = {
{ "FileMenu", NULL, "_File" },
{ "ViewMenu", NULL, "_View" },
{ "Open", GTK_STOCK_OPEN, "_Open", "<control>O", "Open a file", open_action_callback },
{ "Exit", GTK_STOCK_QUIT, "E_xit", "<control>Q", "Exit the program", exit_action_callback },
{ "ZoomIn", GTK_STOCK_ZOOM_IN, "Zoom _In", "plus", "Zoom into the image", zoom_in_action_callback },
{ "ZoomOut", GTK_STOCK_ZOOM_OUT, "Zoom _Out", "minus", "Zoom away from the image", zoom_out_action_callback },
};
/* Toggle items */
static const GtkToggleActionEntry toggle_entries[] = {
{ "FullScreen", NULL, "_Full Screen", "F11", "Switch between full screen and windowed mode", full_screen_action_callback, FALSE }
};
/* Radio items */
static const GtkRadioActionEntry radio_entries[] = {
{ "HighQuality", "my-stock-high-quality", "_High Quality", NULL, "Display images in high quality, slow mode", 0 },
{ "NormalQuality", "my-stock-normal-quality", "_Normal Quality", NULL, "Display images in normal quality", 1 },
{ "LowQuality", "my-stock-low-quality", "_Low Quality", NULL, "Display images in low quality, fast mode", 2 }
};
XML Description
After extracting the actions, you will need to create an XML
description of the actual layout of your menus and toolbars
for use with #GtkUIManager. The following code shows a simple
menu bar that corresponds to the previous
example. Note that the File and
View menus have their names specified in
the action
entries, not in the XML itself. This is because the
XML description only contains identifiers
for the items in the GUI, rather than human-readable names.
static const char *ui_description =
"<ui>"
" <menubar name='MainMenu'>"
" <menu action='FileMenu'>"
" <menuitem action='Open'/>"
" <menuitem action='Exit'/>"
" </menu>"
" <menu action='ViewMenu'>"
" <menuitem action='ZoomIn'/>"
" <menuitem action='ZoomOut'/>"
" <separator/>"
" <menuitem action='FullScreen'/>"
" <separator/>"
" <menuitem action='HighQuality'/>"
" <menuitem action='NormalQuality'/>"
" <menuitem action='LowQuality'/>"
" </menu>"
" </menubar>"
"</ui>";
Creating the Menu Bar
In this last example, we will create a #GtkActionGroup based on the
action entries
we created above. We will then create a #GtkUIManager with the XML description of the menu
layout. We will also extract the accelerator group and the
widgets from the #GtkUIManager put them into a window.
GtkWidget *window;
GtkWidget *vbox;
GtkWidget *menubar;
GtkActionGroup *action_group;
GtkUIManager *ui_manager;
GtkAccelGroup *accel_group;
GError *error;
register_my_stock_icons ();
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
vbox = gtk_vbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (window), vbox);
action_group = gtk_action_group_new ("MenuActions");
gtk_action_group_add_actions (action_group, entries, G_N_ELEMENTS (entries), window);
gtk_action_group_add_toggle_actions (action_group, toggle_entries, G_N_ELEMENTS (toggle_entries), window);
gtk_action_group_add_radio_actions (action_group, radio_entries, G_N_ELEMENTS (radio_entries), 0, radio_action_callback, window);
ui_manager = gtk_ui_manager_new ();
gtk_ui_manager_insert_action_group (ui_manager, action_group, 0);
accel_group = gtk_ui_manager_get_accel_group (ui_manager);
gtk_window_add_accel_group (GTK_WINDOW (window), accel_group);
error = NULL;
if (!gtk_ui_manager_add_ui_from_string (ui_manager, ui_description, -1, &error))
{
g_message ("building menus failed: %s", error->message);
g_error_free (error);
exit (EXIT_FAILURE);
}
menubar = gtk_ui_manager_get_widget (ui_manager, "/MainMenu");
gtk_box_pack_start (GTK_BOX (vbox), menubar, FALSE, FALSE, 0);
gtk_widget_show_all (window);
Registering the icons
Here we show how the register_my_stock_icons() function
used in the previous example could look like.
static struct {
gchar *filename;
gchar *stock_id;
} stock_icons[] = {
{ "high-quality.png", "my-stock-high-quality" },
{ "normal-quality.png", "my-stock-normal-quality" },
{ "low-quality.png", "my-stock-low-quality" },
};
static gint n_stock_icons = G_N_ELEMENTS (stock_icons);
static void
register_my_stock_icons (void)
{
GtkIconFactory *icon_factory;
GtkIconSet *icon_set;
GtkIconSource *icon_source;
gint i;
icon_factory = gtk_icon_factory_new ();
for (i = 0; i < n_stock_icons; i++)
{
icon_set = gtk_icon_set_new ();
icon_source = gtk_icon_source_new ();
gtk_icon_source_set_filename (icon_source, stock_icons[i].filename);
gtk_icon_set_add_source (icon_set, icon_source);
gtk_icon_source_free (icon_source);
gtk_icon_factory_add (icon_factory, stock_icons[i].stock_id, icon_set);
gtk_icon_set_unref (icon_set);
}
gtk_icon_factory_add_default (icon_factory);
g_object_unref (icon_factory);
}