A GtkBuilder is an auxiliary object that reads textual descriptions of a user interface and instantiates the described objects.
In the (unusual) case that you want to add user interface descriptions from multiple sources to the same GtkBuilder you can call Builder to get an empty builder and populate it by (multiple) calls to add_from_file, add_from_resource or add_from_string.
A GtkBuilder holds a reference to all objects that it has constructed and drops these references when it is finalized. This finalization can cause the destruction of non-widget objects or widgets which are not contained in a toplevel window. For toplevel windows constructed by a builder, it is the responsibility of the user to call destroy to get rid of them and all the widgets they contain.
The functions get_object and get_objects can be used to access the widgets in the interface by the names assigned to them inside the UI description. Toplevel windows returned by these functions will stay around until the user explicitly destroys them with destroy. Other widgets will either be part of a larger hierarchy constructed by the builder (in which case you should not have to worry about their lifecycle), or without a parent, in which case they have to be added to some container to make use of them. Non-widget objects need to be reffed with @ref to keep them beyond the lifespan of the builder.
The function connect_signals and variants thereof can be used to connect handlers to the named signals in the description.
GtkBuilder UI Definitions
GtkBuilder parses textual descriptions of user interfaces which are specified in an XML format which can be roughly described by the RELAX NG schema 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. It is common to use `.ui` as the filename extension for files containing GtkBuilder UI definitions.
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 set_translation_domain 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. The target toolkit version(s) are described by <requires> elements, the “lib” attribute specifies the widget library in question (currently the only supported value is “gtk+”) and the “version” attribute specifies the target version in the form “<major>.<minor>”. The builder will error out if the version requirements are not met.
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 function 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 function explictly with the "type-func" attribute. As a special
case, GtkBuilder allows to use an object that has been constructed by a UIManager in
another part of the UI definition by specifying the id of the UIManager in the
“constructor” attribute and the name of the object in the “id” attribute.
Objects may be given a name with the “id” attribute, which allows the application to retrieve them from the builder with get_object. An id is also necessary to use the object as property value in other parts of the UI definition. GTK+ reserves ids starting and ending with ___ (3 underscores) for its own purposes.
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 false), 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 parse).
GVariants can be specified in the format understood by parse, and pixbufs can be specified as a filename of an image file to load.
Objects can be referred to by their name and by default refer to objects declared in the local xml fragment and objects exposed via expose_object. In general, GtkBuilder allows forward references to objects — declared in the local xml; an object doesn’t have to be 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.
It is also possible to bind a property value to another object's property value using the attributes "bind-source" to specify the source object
of the binding, "bind-property" to specify the source property and optionally "bind-flags" to specify the binding flags Internally builder
implement this using GBinding objects. For more information see
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
this can be changed by passing a custom BuilderConnectFunc to
connect_signals_full. The remaining attributes, “after”,
“swapped” and “object”, have the same meaning as the corresponding parameters of the
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 Dialog). 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.
A GtkBuilder UI Definition
<object class="GtkDialog" id="dialog1">
<object class="GtkBox" id="vbox1">
<object class="GtkButtonBox" id="hbuttonbox1">
<object class="GtkButton" id="ok_button">
<signal name="clicked" handler="ok_button_clicked"/>
Beyond this general structure, several object classes define their own XML DTD fragments for filling in the ANY placeholders in the DTD above. Note that a custom element in a <child> element gets parsed by the custom tag handler of the parent object, while a custom element in an <object> element gets parsed by the custom tag handler of the object.
These XML fragments are explained in the documentation of the respective objects.
Additionally, since 3.10 a special <template> tag has been added to the format allowing one to define a widget class’s components. See the GtkWidget documentation for details.