Gnome::Gio::MenuModel

An abstract class representing the contents of a menu

Description

Gnome::Gio::MenuModel represents the contents of a menu – an ordered list of menu items. The items are associated with actions, which can be activated through them. Items can be grouped in sections, and may have submenus associated with them. Both items and sections usually have some representation data, such as labels or icons. The type of the associated action (ie whether it is stateful, and what kind of state it has) can influence the representation of the item.

The conceptual model of menus in Gnome::Gio::MenuModel is hierarchical: sections and submenus are again represented by Gnome::Gio::MenuModels. Menus themselves do not define their own roles. Rather, the role of a particular Gnome::Gio::MenuModel is defined by the item that references it (or, in the case of the ‘root’ menu, is defined by the context in which it is used).

As an example, consider the visible portions of this menu:

There are 8 “menus” visible in the screenshot: one menubar, two submenus and 5 sections:

the toplevel menubar (containing 4 items)
the View submenu (containing 3 sections)
the first section of the View submenu (containing 2 items)
the second section of the View submenu (containing 1 item)
the final section of the View submenu (containing 1 item)
the Highlight Mode submenu (containing 2 sections)
the Sources section (containing 2 items)
the Markup section (containing 2 items)

The example illustrates the conceptual connection between these 8 menus. Each large block in the figure represents a menu and the smaller blocks within the large block represent items in that menu. Some items contain references to other menus.

Notice that the separators visible in the example appear nowhere in the menu model. This is because separators are not explicitly represented in the menu model. Instead, a separator is inserted between any two non-empty sections of a menu. Section items can have labels just like any other item. In that case, a display system may show a section header instead of a separator.

The motivation for this abstract model of application controls is that modern user interfaces tend to make these controls available outside the application. Examples include global menus, jumplists, dash boards, etc. To support such uses, it is necessary to ‘export’ information about actions and their representation in menus, which is exactly what the GActionGroup exporter and the Gnome::Gio::MenuModel exporter do for GActionGroup and Gnome::Gio::MenuModel. The client-side counterparts to make use of the exported information are GDBusActionGroup and GDBusMenuModel.

The API of Gnome::Gio::MenuModel is very generic, with iterators for the attributes and links of an item, see g_menu_model_iterate_item_attributes() and g_menu_model_iterate_item_links(). The ‘standard’ attributes and link types have predefined names: G_MENU_ATTRIBUTE_LABEL, G_MENU_ATTRIBUTE_ACTION, G_MENU_ATTRIBUTE_TARGET, G_MENU_LINK_SECTION and G_MENU_LINK_SUBMENU.

Items in a Gnome::Gio::MenuModel represent active controls if they refer to an action that can get activated when the user interacts with the menu item. The reference to the action is encoded by the string id in the G_MENU_ATTRIBUTE_ACTION attribute. An action id uniquely identifies an action in an action group. Which action group(s) provide actions depends on the context in which the menu model is used. E.g. when the model is exported as the application menu of a Gnome::Gtk3::Application, actions can be application-wide or window-specific (and thus come from two different action groups). By convention, the application-wide actions have names that start with “app.”, while the names of window-specific actions start with “win.”.

While a wide variety of stateful actions is possible, the following is the minimum that is expected to be supported by all users of exported menu information:

an action with no parameter type and no state
an action with no parameter type and boolean state
an action with string parameter type and string state

Stateless

A stateless action typically corresponds to an ordinary menu item. Selecting such a menu item will activate the action (with no parameter).

Boolean State

An action with a boolean state will most typically be used with a “toggle” or “switch” menu item. The state can be set directly, but activating the action (with no parameter) results in the state being toggled.

Selecting a toggle menu item will activate the action. The menu item should be rendered as “checked” when the state is true.

String Parameter and State

Actions with string parameters and state will most typically be used to represent an enumerated choice over the items available for a group of radio menu items. Activating the action with a string parameter is equivalent to setting that parameter as the state.

Radio menu items, in addition to being associated with the action, will have a target value. Selecting that menu item will result in activation of the action with the target value as the parameter. The menu item should be rendered as “selected” when the state of the action is equal to the target value of the menu item.

Synopsis

Declaration

unit class Gnome::Gio::MenuModel;
also is Gnome::GObject::Object;

Uml Diagram

Constants

G_MENU_ATTRIBUTE_ACTION = “action”; The menu item attribute which holds the action name of the item. Action names are namespaced with an identifier for the action group in which the action resides. For example, “win.” for window-specific actions and “app.” for application-wide actions.

See also get_item_attribute() and Gnome::Gio::MenuItem.set_attribute().
G_MENU_ATTRIBUTE_ACTION_NAMESPACE = “action-namespace”; The menu item attribute that holds the namespace for all action names in menus that are linked from this item.
G_MENU_ATTRIBUTE_TARGET = “target”; The menu item attribute which holds the target with which the item’s action will be activated.

See also Gnome::Gio::MenuItem.set_action_and_target().
G_MENU_ATTRIBUTE_LABEL = “label”; The menu item attribute which holds the label of the item.
G_MENU_ATTRIBUTE_ICON = “icon”; The menu item attribute which holds the icon of the item.

This attribute is intended only to represent ‘noun’ icons such as favicons for a webpage, or application icons. It should not be used for ‘verbs’ (ie: stock icons).
G_MENU_LINK_SECTION = “section”; The name of the link that associates a menu item with a section. The linked menu will usually be shown in place of the menu item, using the item’s label as a header.

See also Gnome::Gio::MenuItem.set_link().
G_MENU_LINK_SUBMENU = “submenu”; The name of the link that associates a menu item with a submenu.

See also Gnome::Gio::MenuItem.set_link().

Methods

get-item-attribute-value

Queries the item at position item-index in model for the attribute specified by attribute.

If expected-type is non-undefined then it specifies the expected type of the attribute. If it is undefined then any type will be accepted.

If the attribute exists and matches expected-type (or if the expected type is unspecified) then the value is returned.

If the attribute does not exist, or does not match the expected type then undefined is returned.

Returns: (transfer full): the value of the attribute

method get-item-attribute-value ( Int $item_index, Str $attribute, N-GObject $expected_type --> N-GObject )

Int $item_index; the index of the item
Str $attribute; the attribute to query
N-GObject $expected_type; (nullable): the expected type of the attribute, or undefined

get-item-link

Queries the item at position item-index in model for the link specified by link.

If the link exists, the linked Gnome::Gio::MenuModel is returned. If the link does not exist, undefined is returned.

Returns: (transfer full): the linked Gnome::Gio::MenuModel, or undefined

method get-item-link ( Int $item_index, Str $link --> N-GObject )

Int $item_index; the index of the item
Str $link; the link to query

get-n-items

Query the number of items in model.

method get-n-items ( --> Int )

is-mutable

Queries if model is mutable.

An immutable Gnome::Gio::MenuModel will never emit the items-changed signal. Consumers of the model may make optimisations accordingly.

Returns: True if the model is mutable (ie: “items-changed” may be emitted).

method is-mutable ( --> Bool )

items-changed

Requests emission of the items-changed signal on model.

This function should never be called except by Gnome::Gio::MenuModel subclasses. Any other calls to this function will very likely lead to a violation of the interface of the model.

The implementation should update its internal representation of the menu before emitting the signal. The implementation should further expect to receive queries about the new state of the menu (and particularly added menu items) while signal handlers are running.

The implementation must dispatch this call directly from a mainloop entry and not in response to calls – particularly those from the Gnome::Gio::MenuModel API. Said another way: the menu must not change while user code is running without returning to the mainloop.

method items-changed ( Int $position, Int $removed, Int $added )

Int $position; the position of the change
Int $removed; the number of items removed
Int $added; the number of items added

iterate-item-attributes

Creates a Gnome::Gio::MenuLinkIter to iterate over the attributes of the item at position $item-index in model. You must free the iterator with clear-object() when you are done.

Returns: a new Gnome::Gio::MenuLinkIter

method iterate-item-attributes (
  Int $item_index --> Gnome::Gio::MenuLinkIter
)

Int $item_index; the index of the item

iterate-item-links

Creates a Gnome::Gio::MenuLinkIter to iterate over the links of the item at position item-index in model. You must free the iterator with clear-object() when you are done.

Returns: a new Gnome::Gio::MenuLinkIter

method iterate-item-links (
  Int $item_index --> Gnome::Gio::MenuLinkIter
)

Int $item_index; the index of the item

Signals

There are two ways to connect to a signal. The first option you have is to use register-signal() from Gnome::GObject::Object. The second option is to use connect-object() directly from Gnome::GObject::Signal.

First method

The positional arguments of the signal handler are all obligatory as well as their types. The named attributes :$widget and user data are optional.

# handler method
method mouse-event ( GdkEvent $event, :$widget ) { ... }

# connect a signal on window object
my Gnome::Gtk3::Window $w .= new( ... );
$w.register-signal( self, 'mouse-event', 'button-press-event');

Second method

my Gnome::Gtk3::Window $w .= new( ... );
my Callable $handler = sub (
  N-GObject $native, GdkEvent $event, OpaquePointer $data
) {
  ...
}

$w.connect-object( 'button-press-event', $handler);

Also here, the types of positional arguments in the signal handler are important. This is because both methods register-signal() and connect-object() are using the signatures of the handler routines to setup the native call interface.

Supported signals

items-changed

Emitted when a change has occured to the menu.

The only changes that can occur to a menu is that items are removed or added. Items may not change (except by being removed and added back in the same location). This signal is capable of describing both of those changes (at the same time).

The signal means that starting at the index position, removed items were removed and added items were added in their place. If removed is zero then only items were added. If added is zero then only items were removed.

As an example, if the menu contains items a, b, c, d (in that order) and the signal (2, 1, 3) occurs then the new composition of the menu will be a, b, -, -, -, d (with each - representing some new item).

Signal handlers may query the model (particularly the added items) and expect to see the results of the modification that is being reported. The signal is emitted after the modification.

method handler (
  Int $position,
  Int $removed,
  Int $added,
  Int :$_handle_id,
  Gnome::GObject::Object :_widget($model),
  *%user-options
);

$model; the Gnome::Gio::MenuModel that is changing
$position; the position of the change
$removed; the number of items removed
$added; the number of items added

Gnome::Gio::MenuModel

Description

An example menu

Stateless

Boolean State

String Parameter and State

See Also

Synopsis

Declaration

Uml Diagram

Constants

Methods

get-item-attribute-value

get-item-link

get-n-items

is-mutable

items-changed

iterate-item-attributes

iterate-item-links

Signals

First method

Second method

Supported signals

items-changed