Federico Mena-Quintero

federico@ximian.com

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.

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 }.

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.

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. The following code shows a declaration of a simple menu bar to be used with gnome_app_fill_menu() or similar. The menu hierarchy looks like this: File Open — Exit View Zoom In Zoom 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_NONE, NULL, 0, 0, NULL }, { GNOME_APP_UI_ITEM, "_Normal Quality", "Display images in normal quality", normal_quality_callback, NULL, NULL, GNOME_APP_PIXMAP_NONE, NULL, 0, 0, NULL }, { GNOME_APP_UI_ITEM, "_Low Quality", "Display images in low quality, fast mode", low_quality_callback, NULL, NULL, GNOME_APP_PIXMAP_NONE, NULL, 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 } } 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 gdk_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 GtkActionEntry entries[] = { { "FileMenu", NULL, "_File" }, { "ViewMenu", NULL, "_View" }, { "Open", GTK_STOCK_OPEN, "_Open", "<control>O", "Open a file", open_action_callback }, { "Exit", GTK_STOCK_OPEN, "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 GtkToggleActionEntry toggle_entries[] = { { "FullScreen", NULL, "_Full Screen", "F11", "Switch between full screen and windowed mode", full_screen_action_callback, FALSE } }; /* Radio items */ static GtkRadioActionEntry radio_entries[] = { { "HighQuality", NULL, "_High Quality", NULL, "Display images in high quality, slow mode", 0 }, { "NormalQuality", NULL, "_Normal Quality", NULL, "Display images in normal quality", 1 }, { "LowQuality", NULL, "_Low Quality", NULL, "Display images in low quality, fast mode", 2 } }; 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>"; 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; 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);