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Migrating from old menu and toolbar systems to GtkAction

Federico Mena-Quintero

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 }.

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