gobject:object, common-lisp:standard-object, common-lisp:t

None

The gtk:builder object reads XML descriptions of a user interface and instantiates the described objects. To create a gtk:builder object from a user interface description, call the gtk:builder-new-from-file, gtk:builder-new-from-resource or gtk:builder-new-from-string function.

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same gtk:builder object you can call the gtk:builder-new function to get an empty builder and populate it by (multiple) calls to the gtk:builder-add-from-file, gtk:builder-add-from-resource or gtk:builder-add-from-string functions.

The gtk:builder object 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 the gtk:window-destroy function to get rid of them and all the widgets they contain.

The gtk:builder-object and gtk:builder-objects functions 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 the gtk:window-destroy function. 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 the g:object-ref function to keep them beyond the lifespan of the builder.

GtkBuilder UI Definitions

The gtk:builder object 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.

Structure of UI definitions

UI definition files are always encoded in UTF-8. The toplevel element is <interface>. It optionally takes a "domain" attribute, which will make the builder look for translated strings using the dgettext() function in the domain specified. This can also be done by calling the gtk:builder-translation-domain function on the builder. For example:

<?xml version="1.0" encoding="UTF-8">
<interface domain="your-app">
  ...
</interface>  

Requirements

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 gtk:builder object will error out if the version requirements are not met. For example:

<?xml version="1.0" encoding="UTF-8">
<interface domain="your-app">
  <requires lib="gtk" version="4.0" />
</interface>  

Objects

Objects are defined as children of the <interface> element. 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, for example, 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 type initializer from the class name by applying heuristics. This works in most cases, but if necessary, it is possible to specify the name of the type initializer explicitly with the "type-func" attribute. If your UI definition is referencing internal types, you should make sure to call the g:type-ensure function for each object type before parsing the UI definition.

Objects may be given a name with the "id" attribute, which allows the application to retrieve them from the builder with the gtk:builder-object function. 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.

Properties

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. For example:

<object class="GtkButton">
  <property name="label">Hello, world</property>
</object>  

If the "translatable" attribute is set to a true value, GTK uses the gettext() function, or the dgettext() function 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. For example:

<object class="GtkButton">
  <property name="label"
            translatable="yes"
            context="button">Hello, world</property>
</object>  

The gtk:builder object 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 values, strings like "FALSE", "f", "no", "n", "0" are interpreted as false values
• enumeration types, can be specified by their full C identifier their short name used when registering the enumeration type, or their integer value
• flag types, can be specified by their C identifier, short name, integer value, and optionally combined with "|" for bitwise OR, for example, "GTK_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE", or "emoji|lowercase"
• colors, in a format understood by the gdk:rgba-parse function
• g:variant parameters, can be specified in the format understood by the g:variant-parse function
• pixbufs, can be specified as an object ID, a resource path or a filename of an image file to load relative to the builder file or the current working directory if the gtk:builder-add-from-string function was used
• g:file objects like pixbufs, can be specified as an object ID, a URI or a filename of a file to load relative to the builder file or the current working directory if the gtk:builder-add-from-string function was used

Objects can be referred to by their name and by default refer to objects declared in the local XML fragment and objects exposed with the gtk:builder-expose-object function. In general, the gtk:builder object allows forward references to objects declared in the local XML. An object does not 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.

Child objects

Many widgets have properties for child widgets, such as the child property of the gtk:expander widget. In this case, the preferred way to specify the child widget in a UI definition file is to simply set the property:

<object class="GtkExpander">
  <property name="child">
    <object class="GtkLabel">
    ...
    </object>
  </property>
</object>  

Generic containers that can contain an arbitrary number of children, such as the gtk:box widget instead use the <child> element. A <child> element contains an <object> element which describes the child object. Most often, child objects are widgets inside a container, but they can also be, for example, actions in an action group, or columns in a tree model.

Any object type that implements the gtk:buildable interface can specify how children may be added to it. Since many objects and widgets that are included with GTK already implement the gtk:buildable interface, typically child objects can be added using the <child> element without having to be concerned about the underlying implementation.

See the gtk:widget documentation for many examples of using the gtk:builder object with widgets, including setting child objects using the <child> element.

A noteworthy special case to the general rule that only objects implementing the gtk:buildable interface may specify how to handle the <child> element is that the gtk:builder object provides special support for adding objects to a g:list-store object by using the <child> element. For instance:

<object class="GListStore">
  <property name="item-type">MyObject</property>
  <child>
    <object class="MyObject"/>
  </child>
  ...
</object>  

Property bindings

It is also possible to bind a property value to another object’s property value using the "bind-source" attribute to specify the source object of the binding, and optionally, "bind-property" and "bind-flags" attributes to specify the source property and source binding flags respectively. Internally, the gtk:builder class implements this using g:binding objects.

For instance, in the example below the "label" property of the bottom_label widget is bound to the "label" property of the top_button widget:

<object class="GtkBox">
  <property name="orientation">vertical</property>
  <child>
    <object class="GtkButton" id="top_button">
      <property name="label">Hello, world</property>
    </object>
  </child>
  <child>
    <object class="GtkLabel" id="bottom_label">
      <property name="label"
                bind-source="top_button"
                bind-property="label"
                bind-flags="sync-create"/>
    </object>
  </child>
</object>  

For more information, see the documentation of the g:object-bind-property method.

Please note that another way to set up bindings between objects in .ui files is to use the gtk:expression methodology. See the gtk:expression documentation for more information.

Internal children

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, for example, the content area of a the gtk:dialog widget. This can be achieved by setting the "internal-child" property of the <child> element to a true value. Note that the gtk:builder object still requires an <object> element for the internal child, even if it has already been constructed.

Specialized children

Some widgets have different places where a child can be added, for example, tabs versus 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.

<object class="GtkButton" id="hello_button">
  <signal name="clicked" handler="hello_button__clicked" />
</object>  

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:

• "after" matches the :after flag, and will ensure that the handler is called after the default class closure for the signal
• "swapped" matches the :swapped flag, and will swap the instance and closure arguments when invoking the signal handler
• "object" will bind the signal handler to the lifetime of the object referenced by the attribute

By default "swapped" will be set to "yes" if not specified otherwise, in the case where "object" is set, for convenience. A "last_modification_time" attribute is also allowed, but it does not have a meaning to the builder.

Example UI Definition

<interface>
  <object class="GtkDialog" id=dialog1">
    <child internal-child="content_area">
      <object class="GtkBox">
        <child internal-child="action_area">
          <object class="GtkBox">
            <child>
              <object class="GtkButton" id="ok-button">
                <property name="label" translatable="yes">_Ok</property>
                <property name="use-underline">True</property>
                <signal name="clicked" handler="ok-button-clicked" object="ok-button"/>
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>  

Using GtkBuildable for extending UI definitions

Objects can implement the gtk:buildable interface to add custom elements and attributes to the XML. Typically, any extension will be documented in each type that implements the interface.

Templates

When describing a gtk:widget object, you can use the <template> tag to describe a UI bound to a specific widget type. GTK will automatically load the UI definition when instantiating the type, and bind children and signal handlers to instance fields and function symbols. For more information, see the gtk:widget documentation.