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 (requires|object)* >
<!ELEMENT object    (property|signal|child|ANY)* >
<!ELEMENT property  PCDATA >
<!ELEMENT signal    EMPTY >
<!ELEMENT requires  EMPTY >
<!ELEMENT child     (object|ANY*) >
<!ATTLIST interface domain                 #IMPLIED >
<!ATTLIST object    id                     #REQUIRED
                    class                  #REQUIRED
                    type-func              #IMPLIED
                    constructor            #IMPLIED >
<!ATTLIST requires  lib                    #REQUIRED
                    version                #REQUIRED >
<!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 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() 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 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 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 gtk.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 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.

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(). 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.

A gtk.Builder UI definition example

<interface>
  <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>
            <child>
              <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"/>
              </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 <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 their respective objects in the GTK+ Reference Manual.

gtk.Builder.add_from_file

    def add_from_file(filename)

The add_from_file() method parses a file containing a GtkBuilder UI definition and merges it with the current contents of builder.

gtk.Builder.add_from_string

    def add_from_string(buffer)

The add_from_string() method parses a string containing a GtkBuilder UI definition and merges it with the current contents of builder.

gtk.Builder.add_objects_from_file

    def add_objects_from_file(filename, object_ids)

The add_objects_from_file() method parses a file containing a GtkBuilder UI definition building only the requested objects and merges it with the current contents of builder.

Note that if you are adding an object that depends on an object that is not its child (for instance a gtk.TreeView that depends on its gtk.TreeModel), you have to explicitely list all of them in object_ids.

gtk.Builder.add_objects_from_string

    def add_objects_from_string(buffer, object_ids)

The add_objects_from_string() method parses a string containing a GtkBuilder UI definition building only the requested objects and merges it with the current contents of builder.

Note that if you are adding an object that depends on an object that is not its child (for instance a gtk.TreeView that depends on its gtk.TreeModel), you have to explicitely list all of them in object_ids.

gtk.Builder.connect_signals

    def connect_signals(object, user_data)

The connect_signals() method uses Python's introspective features to look at the keys (if object is a mapping) or attributes (if object is an instance) and tries to match them with the signal handler names given in the interface description. The callbacks referenced by each matched key or attribute are connected to their matching signals.

For each of handlers that cannot be found, a RuntimeWarning is issued. Also, if there is at least one such missing handler, connect_signals will return a list of their names, else return value is None.

gtk.Builder.get_object

    def get_object(name)

The get_object() method gets the object named name.

gtk.Builder.get_objects

    def get_objects()

The get_objects() method gets all objects that have been constructed by builder.

gtk.Builder.get_translation_domain

    def get_translation_domain()

The get_translation_domain() gets the translation domain of builder.

gtk.Builder.get_type_from_name

    def get_type_from_name(type_name)

The get_type_from_name() method looks up a type by name, using the virtual function that GtkBuilder has for that purpose.

gtk.Builder.set_translation_domain

    def set_translation_domain(domain)

The set_translation_domain() method sets the translation domain of builder. See GtkBuilder:translation-domain property.