Constructing menus and toolbars from an XML description

• Module available since Gtk+ version 2.4

A UIManager constructs a user interface (menus and toolbars) from one or more UI definitions, which reference actions from one or more action groups.

The UI definitions are specified in an XML format which can be roughly described by the following DTD.

<!ELEMENT ui (menubar|toolbar|popup|accelerator)* >
<!ELEMENT menubar (menuitem|separator|placeholder|menu)* >
<!ELEMENT menu (menuitem|separator|placeholder|menu)* >
<!ELEMENT popup (menuitem|separator|placeholder|menu)* >
<!ELEMENT toolbar (toolitem|separator|placeholder)* >
<!ELEMENT placeholder (menuitem|toolitem|separator|placeholder|menu)* >
<!ELEMENT menuitem EMPTY >
<!ELEMENT toolitem EMPTY >
<!ELEMENT separator EMPTY >
<!ELEMENT accelerator EMPTY >
<!ATTLIST menubar name #IMPLIED
action #IMPLIED >
<!ATTLIST toolbar name #IMPLIED
action #IMPLIED >
<!ATTLIST popup name #IMPLIED
action #IMPLIED >
<!ATTLIST placeholder name #IMPLIED
action #IMPLIED
expand (true|false) #IMPLIED >
<!ATTLIST separator name #IMPLIED
action #IMPLIED >
<!ATTLIST menu name #IMPLIED
action #REQUIRED
position (top|bot) #IMPLIED >
<!ATTLIST menuitem name #IMPLIED
action #REQUIRED
position (top|bot) #IMPLIED >
<!ATTLIST toolitem name #IMPLIED
action #REQUIRED
position (top|bot) #IMPLIED >
<!ATTLIST accelerator name #IMPLIED
action #REQUIRED >

There are some additional restrictions beyond those specified in the DTD, e.g. every toolitem must have a toolbar in its anchestry and every menuitem must have a menubar or popup in its anchestry. Since a GMarkup parser is used to parse the UI description, it must not only be valid XML, but valid GMarkup.

If a name is not specified, it defaults to the action. If an action is not specified either, the element name is used. The name and action attributes must not contain '/' characters after parsing (since that would mess up path lookup) and must be usable as XML attributes when enclosed in doublequotes, thus they must not '"' characters or references to the " entity.

<ui>
<menubar>
<menu name="FileMenu" action="FileMenuAction">
<menuitem name="New" action="New2Action" />
<placeholder name="FileMenuAdditions" />
</menu>
<menu name="JustifyMenu" action="JustifyMenuAction">
<menuitem name="Left" action="justify-left"/>
<menuitem name="Centre" action="justify-center"/>
<menuitem name="Right" action="justify-right"/>
<menuitem name="Fill" action="justify-fill"/>
</menu>
</menubar>
<toolbar action="toolbar1">
<placeholder name="JustifyToolItems">
<separator/>
<toolitem name="Left" action="justify-left"/>
<toolitem name="Centre" action="justify-center"/>
<toolitem name="Right" action="justify-right"/>
<toolitem name="Fill" action="justify-fill"/>
<separator/>
</placeholder>
</toolbar>
</ui>

The most remarkable feature of UIManager is that it can overlay a set of menuitems and toolitems over another one, and demerge them later.

Merging is done based on the names of the XML elements. Each element is identified by a path which consists of the names of its anchestors, separated by slashes. For example, the menuitem named "Left" in the example above has the path /ui/menubar/JustifyMenu/Left and the toolitem with the same name has path /ui/toolbar1/JustifyToolItems/Left.

Every action has an accelerator path. Accelerators are installed together with menuitem proxies, but they can also be explicitly added with <accelerator> elements in the UI definition. This makes it possible to have accelerators for actions even if they have no visible proxies.

The separators created by UIManager are "smart", i.e. they do not show up in the UI unless they end up between two visible menu or tool items. Separators which are located at the very beginning or end of the menu or toolbar containing them, or multiple separators next to each other, are hidden. This is a useful feature, since the merging of UI elements from multiple sources can make it hard or impossible to determine in advance whether a separator will end up in such an unfortunate position.

For separators in toolbars, you can set expand="true" to turn them from a small, visible separator to an expanding, invisible one. Toolitems following an expanding separator are effectively right-aligned.

Submenus pose similar problems to separators inconnection with merging. It is impossible to know in advance whether they will end up empty after merging. UIManager offers two ways to treat empty submenus:

• make them disappear by hiding the menu item they're attached to
• add an insensitive "Empty" item

The behaviour is chosen based on the "hide_if_empty" property of the action to which the submenu is associated.

| GObject
| +----UIManager