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class Gtk::Builder

Since 2.12


A GtkBuilder is an auxiliary object that reads textual descriptions of a user interface and instantiates the described objects. To pass a description to a Gtk::Builder, call Gtk::Builder#add and Gtk::Builder#<<. If they fail to detect a description type, use Gtk::Builder#add_from_file or Gtk::Builder#add_from_string. These methods can be called multiple times; the builder merges the content of all descriptions.

A Gtk::Builder 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::Widget#destroy to get rid of them and all the widgets they contain.

The functions Gtk::Builder#[], Gtk::Builder#get_object and Gtk::Builder#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::Widget#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.

The function Gtk::Builder#connect_signals can be used to connect handlers to the named signals in the description.

Gtk::Builder UI Definitions

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 Gtk::Builder UI definitions or just UI definitions if the context is clear. Do not confuse Gtk::Builder UI Definitions with Gtk::UIManager 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
                     class                      #REQUIRED
                     type-func                  #IMPLIED
                     constructor                #IMPLIED >
<!ATTLIST property   name                       #REQUIRED
                     translatable               #IMPLIED
                     comments                   #IMPLIED
                     context                    #IMPLIED >
<!ATTLIST signal     name                       #REQUIRED
                     handler                    #REQUIRED
                     after                      #IMPLIED
                     swapped                    #IMPLIED
                     object                     #IMPLIED
                     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 Gtk::Builder#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.

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, Gtk::Builder allows to use an object that has been constructed by a Gtk::UIManager in another part of the UI definition by specifying the id of the Gtk::UIManager 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#[]. 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.

Gtk::Builder 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 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, Gtk::Builder 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 method 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.

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 Gtk::Dialog). This can be achieved by setting the "internal-child" propery of the <child> element to a true value. Note that Gtk::Builder 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.

Example 51. A Gtk::Builder UI Definition

  <object class="GtkDialog" id="dialog1">
    <child internal-child="vbox">
      <object class="GtkVBox" id="vbox1">
        <property name="border-width">10</property>
        <child internal-child="action_area">
          <object class="GtkHButtonBox" id="hbuttonbox1">
            <property name="border-width">20</property>
              <object class="GtkButton" id="ok_button">
                <property name="label">gtk-ok</property>
                <property name="use-stock">TRUE</property>
                <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, see Gtk::Widget, Gtk::Container, Gtk::Dialog, Gtk::CellLayout, Gtk::ColorSelectionDialog, Gtk::FontSelectionDialog, Gtk::ComboBoxEntry, Gtk::Expander, Gtk::Frame, Gtk::ListStore, Gtk::TreeStore, Gtk::Notebook, Gtk::SizeGroup, Gtk::TreeView, Gtk::UIManager, Gtk::ActionGroup.

Class Methods
Creates a new builder object.

Instance Methods


Parses a file or string containing a Gtk::Builder UI Definitions and merges it with the current contents of self.

If the argument starts with "<" or includes a new line, the argument is processed ass ui_definition otherwise filename.

  • filename: the name of the file to parse
  • ui_definistion: the string to parse
  • Returns: self
Same as <<.
  • filename: the name of the file to parse
  • ui_definistion: the string to parse
  • Returns: self
Parses a file containing a Gtk::Builder UI Definitions and merges it with the current contents of self.
  • filename: the name of the file to parse
  • Returns: self
Parses a string containing a Gtk::Builder UI Definitions and merges it with the current contents of self.
  • ui_definistion: the string to parse
  • Returns: self
Gets the object named name. Note that this function does not increment the reference count of the returned object.
  • name: name of object to get
  • Returns: the object named name or nil if it could not be found in the object tree.
Gets all objects that have been constructed by self.
  • Returns: an array containing all the objects constructed by the Gtk::Builder instance.
connect_signals {|handler_name| ...}
Is an callback method. The given block should returns a callbale object (e.g. Proc object) corresponding handler_name.
  • handler_name: name of handler to be connected
Looks up a type by name, using the virtual function that Gtk::Builder has for that purpose. This is mainly used when implementing the Gtk::Buildable interface on a type.
  • type_name: type name to lookup
  • Returns: the class found for type_name or nil if no type was found
Same as translation_domain=.
  • translation_domain: The translation domain used by gettext
  • Returns: self
Gets the translation domain used by gettext.
  • Returns: The translation domain used by gettext
Sets the translation domain used by gettext.
  • translation_domain: The translation domain used by gettext
  • Returns: translation_domain


translation-domain: String (Read/Write)
The translation domain used by gettext


  • 2008-04-10 kou: created.
Last modified:2008/04/11 00:07:13
References:[News (2016-04-04 No.1)] [News_20100923_1] [Ruby/GTK] [index-ruby-gtk2] [Gtk::Builder] [api-gtk-index] [News (2015-10-04 No.1)] [Gtk::Buildable]