gtk.Builder UI definition
gtk.Builder parses textual
descriptions of user interfaces which are specified in an XML format which
can be roughly described by the DTD below. We refer to these descriptions as GtkBuilder UI definitions
or just UI definitions if the context is clear. Do not confuse GtkBuilder UI Definitions with
GtkUIManager UI Definitions, which are more limited in scope.
<!ELEMENT interface object* >
<!ELEMENT object (property|signal|child|ANY)* >
<!ELEMENT property PCDATA >
<!ELEMENT signal EMPTY >
<!ELEMENT child (object|ANY*) >
<!ATTLIST interface domain #IMPLIED >
<!ATTLIST object id #REQUIRED
constructor #IMPLIED >
<!ATTLIST property name #REQUIRED
context #IMPLIED >
<!ATTLIST signal name #REQUIRED
last_modification_time #IMPLIED >
<!ATTLIST child type #IMPLIED
internal-child #IMPLIED >
The toplevel element is <interface>. It optionally takes a "domain" attribute,
which will make the builder look for translated strings using dgettext() in the domain
specified. This can also be done by calling
on the builder. Objects are described by <object> elements, which can contain <property>
elements to set properties, <signal> elements which connect signals to handlers, and <child>
elements, which describe child objects (most often widgets inside a container, but also e.g. actions
in an action group, or columns in a tree model). A <child> element contains an <object>
element which describes the child object.
Typically, the specific kind of object represented by an <object> element is specified by the
"class" attribute. If the type has not been loaded yet, GTK+ tries to find the _get_type() from the
class name by applying heuristics. This works in most cases, but if necessary, it is possible to specify
the name of the _get_type() explictly with the "type-func" attribute. As a special case, GtkBuilder allows
to use an object that has been constructed by a GtkUIManager in another part of the UI definition by
specifying the id of the GtkUIManager in the "constructor" attribute and the name of the object
in the "id" attribute.
Objects must be given a name with the "id" attribute, which allows the application to retrieve them from
the builder with gtk_builder_get_object(). An id is also necessary to use the object as property
value in other parts of the UI definition.
Setting properties of objects is pretty straightforward with the <property>element: the "name"
attribute specifies the name of the property, and the content of the element specifies the value. If the
"translatable" attribute is set to a true value, GTK+ uses gettext() (or dgettext() if the builder has
a translation domain set) to find a translation for the value. This happens before the value is parsed,
so it can be used for properties of any type, but it is probably most useful for string properties.
It is also possible to specify a context to disambiguate short strings, and comments which may
help the translators.
GtkBuilder can parse textual representations for the most common property types: characters, strings,
integers, floating-point numbers, booleans (strings like "TRUE", "t", "yes", "y", "1" are interpreted as
True, strings like "FALSE, "f", "no", "n", "0" are interpreted as
enumerations (can be specified by their name, nick or integer value), flags (can be specified by their
name, nick, integer value, optionally combined with "|", e.g. "gtk.VISIBLE|gtk.REALIZED")
and colors (in a format understood by gdk_color_parse()). Objects can be referred to by their name.
Pixbufs can be specified as a filename of an image file to load. In general, GtkBuilder allows
forward references to objects — an object doesn't have to constructed before it can be referred to.
The exception to this rule is that an object has to be constructed before it can be used as the value
of a construct-only property.
Signal handlers are set up with the <signal> element. The "name" attribute specifies the name
of the signal, and the "handler" attribute specifies the function to connect to the signal. By default,
GTK+ tries to find the handler using g_module_symbol(), but this can be changed by passing a custom
GtkBuilderConnectFunc to gtk_builder_connect_signals_full(). The remaining attributes, "after", "swapped"
and "object", have the same meaning as the corresponding parameters of the g_signal_connect_object() or
g_signal_connect_data() functions. A "last_modification_time" attribute is also allowed, but it does not
have a meaning to the builder.
Sometimes it is necessary to refer to widgets which have implicitly been constructed by GTK+ as part of
a composite widget, to set properties on them or to add further children (e.g. the vbox of a GtkDialog).
This can be achieved by setting the "internal-child" propery of the <child> element to a true value.
Note that GtkBuilder still requires an <object> element for the internal child, even if it has
already been constructed.
A number of widgets have different places where a child can be added (e.g. tabs vs. page content in
notebooks). This can be reflected in a UI definition by specifying the "type" attribute on a
<child> The possible values for the "type" attribute are described in the sections describing
the widget-specific portions of UI definitions.