### Class

# Gtk Builder

#### Description [src]

    final class Gtk.Builder : GObject.Object {
      /* No available fields */
    }

A `GtkBuilder` reads XML descriptions of a user interface and instantiates the described objects.

To create a `GtkBuilder` from a user interface description, call gtk_builder_new_from_file(), gtk_builder_new_from_resource() or gtk_builder_new_from_string().

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same `GtkBuilder` you can call gtk_builder_new() to get an empty builder and populate it by (multiple) calls to gtk_builder_add_from_file(), gtk_builder_add_from_resource() or gtk_builder_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 gtk_window_destroy() to get rid of them and all the widgets they contain.

The functions gtk_builder_get_object() and gtk_builder_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 gtk_window_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 g_object_ref() to keep them beyond the lifespan of the builder.

# GtkBuilder UI Definitions

`GtkBuilder` parses textual descriptions of user interfaces which are specified in XML format. We refer to these descriptions as “GtkBuilder UI definitions” or just “UI definitions” if the context is clear.

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 gtk_builder_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>`”. `GtkBuilder` 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 explicitly with the “type-func” attribute.

Objects may 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. GTK reserves ids starting and ending with `___` (three consecutive 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_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE”) and colors (in a format understood by gdk_rgba_parse()).

`GVariant`s can be specified in the format understood by g_variant_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 gtk_builder_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, and optionally, “bind-property” and “bind-flags” to specify the source property and source binding flags respectively. Internally, `GtkBuilder` implements this using `GBinding` objects. For more information see g_object_bind_property().

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 content area of a `GtkDialog`). This can be achieved by setting the “internal-child” property 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.

# Signal handlers and function pointers

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. 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.

If you rely on `GModule` support to lookup callbacks in the symbol table, the following details should be noted:

When compiling applications for Windows, you must declare signal callbacks with `G_MODULE_EXPORT`, or they will not be put in the symbol table. On Linux and Unix, this is not necessary; applications should instead be compiled with the -Wl,—export-dynamic `CFLAGS`, and linked against `gmodule-export-2.0`.

# A GtkBuilder UI Definition

    <interface>
      <object class="GtkDialog" id="dialog1">
        <child internal-child="vbox">
          <object class="GtkBox" id="vbox1">
            <child internal-child="action_area">
              <object class="GtkBox" id="hbuttonbox1">
                <child>
                  <object class="GtkButton" id="ok_button">
                    <property name="label">gtk-ok</property>
                    <signal name="clicked" handler="ok_button_clicked"/>
                  </object>
                </child>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

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 element gets parsed by the custom tag handler of the parent object, while a custom element in an

These XML fragments are explained in the documentation of the respective objects.

A `<template>` tag can be used to define a widget class’s components. See the GtkWidget documentation for details.

#### Hierarchy

#### Ancestors

- GObject

#### Constructors

###### gtk_builder_new

Creates a new empty builder object.

###### gtk_builder_new_from_file

Parses the UI definition in the file `filename`.

###### gtk_builder_new_from_resource

Parses the UI definition at `resource_path`.

###### gtk_builder_new_from_string

Parses the UI definition in `string`.

#### Instance methods

###### gtk_builder_add_from_file

Parses a file containing a UI definition and merges it with the current contents of `builder`.

###### gtk_builder_add_from_resource

Parses a resource file containing a UI definition and merges it with the current contents of `builder`.

###### gtk_builder_add_from_string

Parses a string containing a UI definition and merges it with the current contents of `builder`.

###### gtk_builder_add_objects_from_file

Parses a file containing a UI definition building only the requested objects and merges them with the current contents of `builder`.

###### gtk_builder_add_objects_from_resource

Parses a resource file containing a UI definition, building only the requested objects and merges them with the current contents of `builder`.

###### gtk_builder_add_objects_from_string

Parses a string containing a UI definition, building only the requested objects and merges them with the current contents of `builder`.

###### gtk_builder_create_closure

Creates a closure to invoke the function called `function_name`.

###### gtk_builder_expose_object

Add `object` to the `builder` object pool so it can be referenced just like any other object built by builder.

###### gtk_builder_extend_with_template

Main private entry point for building composite components from template XML.

###### gtk_builder_get_current_object

Gets the current object set via gtk_builder_set_current_object().

###### gtk_builder_get_object

Gets the object named `name`.

###### gtk_builder_get_objects

Gets all objects that have been constructed by `builder`.

###### gtk_builder_get_scope

Gets the scope in use that was set via gtk_builder_set_scope().

###### gtk_builder_get_translation_domain

Gets the translation domain of `builder`.

###### gtk_builder_get_type_from_name

Looks up a type by name.

###### gtk_builder_set_current_object

Sets the current object for the `builder`.

###### gtk_builder_set_scope

Sets the scope the builder should operate in.

###### gtk_builder_set_translation_domain

Sets the translation domain of `builder`.

###### gtk_builder_value_from_string

Demarshals a value from a string.

###### gtk_builder_value_from_string_type

Demarshals a value from a string.

#### Properties

###### Gtk.Builder:current-object

The object the builder is evaluating for.

###### Gtk.Builder:scope

The scope the builder is operating in.

###### Gtk.Builder:translation-domain

The translation domain used when translating property values that have been marked as translatable.

#### Class structure

    struct GtkBuilderClass {
      /* no available fields */
    }