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 }.
