Gtk.Builder¶

class — extends GObject.Object

Reads XML descriptions of a user interface and instantiates the described objects.

To create a GtkBuilder from a user interface description, call Builder.new_from_file, Builder.new_from_resource or 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 Builder.new to get an empty builder and populate it by (multiple) calls to Builder.add_from_file, Builder.add_from_resource or 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 Window.destroy to get rid of them and all the widgets they contain.

The functions Builder.get_object and 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 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 GObject.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.

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 dgettext() in the domain specified. This can also be done by calling Builder.set_translation_domain 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>”. GtkBuilder 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.

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. If your UI definition is referencing internal types, you should make sure to call g_type_ensure() 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 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.

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:

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

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:

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

The xgettext tool that is part of gettext can extract these strings, but note that it only looks for translatable="yes".

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 values, strings like “FALSE”, “f”, “no”, “n”, “0” are interpreted as false values)
string lists (separated by newlines)
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 or short name, optionally combined with “|” for bitwise OR, or a single integer value e.g., “GTK_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE”, or “emoji|lowercase” or 520).
colors (in the format understood by Gdk.RGBA.parse)
transforms (in the format understood by Gsk.Transform.parse)
Pango attribute lists (in the format understood by Pango.AttrList.to_string)
Pango tab arrays (in the format understood by Pango.TabArray.to_string)
Pango font descriptions (in the format understood by Pango.FontDescription.from_string)
GVariant (in the format understood by GLib.Variant.parse)
textures (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 CWD if Builder.add_from_string was used)
GFile (like textures, can be specified as an object id, a URI or a filename of a file to load relative to the Builder file or the CWD if Builder.add_from_string 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 via 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.

Child objects¶

Many widgets have properties for child widgets, such as Expander.child. In this case, the preferred way to specify the child widget in a ui 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 Box 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, e.g., actions in an action group, or columns in a tree model.

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

See the GtkWidget documentation for many examples of using GtkBuilder with widgets, including setting child objects using the <child> element.

A noteworthy special case to the general rule that only objects implementing GtkBuildable may specify how to handle the <child> element is that GtkBuilder provides special support for adding objects to a Gio.ListStore 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 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 GObject.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 GObject.Object.bind_property method.

Please note that another way to set up bindings between objects in .ui files is to use the GtkExpression methodology. See the GtkExpression 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 (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.

Specialized children¶

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.

<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 GObject.signal_connect_object or GObject.signal_connect_data functions:

“after” matches the G_CONNECT_AFTER flag, and will ensure that the handler is called after the default class closure for the signal
“swapped” matches the G_CONNECT_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.

When compiling applications for Windows, you must declare signal callbacks with the G_MODULE_EXPORT decorator, or they will not be put in the symbol table:

G_MODULE_EXPORT void
hello_button__clicked (GtkButton *button,
                       gpointer data)
{
  // ...
}

On Linux and Unix, this is not necessary; applications should instead be compiled with the -Wl,--export-dynamic argument inside their compiler flags, and linked against gmodule-export-2.0.

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>
            </child>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>

Using GtkBuildable for extending UI definitions¶

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

Menus¶

In addition to objects with properties that are created with <object> and <property> elements, GtkBuilder also allows to parse XML menu definitions as used by Gio.Menu when exporting menu models over D-Bus, and as described in the PopoverMenu documentation. Menus can be defined as toplevel elements, or as property values for properties of type GMenuModel.

Templates¶

When describing a Widget, 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 GtkWidget documentation for details.

Constructors¶

new¶

@classmethod
def new(cls) -> Builder

Creates a new empty builder object.

This function is only useful if you intend to make multiple calls to Builder.add_from_file, Builder.add_from_resource or Builder.add_from_string in order to merge multiple UI descriptions into a single builder.

new_from_file¶

@classmethod
def new_from_file(cls, filename: str | bytes | os.PathLike[str] | os.PathLike[bytes]) -> Builder

Parses the UI definition in the file filename.

If there is an error opening the file or parsing the description then the program will be aborted. You should only ever attempt to parse user interface descriptions that are shipped as part of your program.

Parameters:

filename — filename of user interface description file

new_from_resource¶

@classmethod
def new_from_resource(cls, resource_path: str) -> Builder

Parses the UI definition at resource_path.

If there is an error locating the resource or parsing the description, then the program will be aborted.

Parameters:

resource_path — a GResource resource path

new_from_string¶

@classmethod
def new_from_string(cls, string: str, length: int) -> Builder

Parses the UI definition in string.

If string is None-terminated, then length should be -1. If length is not -1, then it is the length of string.

If there is an error parsing string then the program will be aborted. You should not attempt to parse user interface description from untrusted sources.

Parameters:

string — a user interface (XML) description
length — the length of string, or -1

Methods¶

add_from_file¶

def add_from_file(self, filename: str | bytes | os.PathLike[str] | os.PathLike[bytes]) -> bool

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

This function is useful if you need to call Builder.set_current_object) to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want Builder.new_from_file instead.

If an error occurs, 0 will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_FILE_ERROR domains.

It’s not really reasonable to attempt to handle failures of this call. You should not use this function with untrusted files (ie: files that are not part of your application). Broken GtkBuilder files can easily crash your program, and it’s possible that memory was leaked leading up to the reported failure. The only reasonable thing to do when an error is detected is to call g_error().

Parameters:

filename — the name of the file to parse

add_from_resource¶

def add_from_resource(self, resource_path: str) -> bool

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

This function is useful if you need to call Builder.set_current_object to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want Builder.new_from_resource instead.

If an error occurs, 0 will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_RESOURCE_ERROR domain.

It’s not really reasonable to attempt to handle failures of this call. The only reasonable thing to do when an error is detected is to call g_error().

Parameters:

resource_path — the path of the resource file to parse

add_from_string¶

def add_from_string(self, buffer: str, length: int) -> bool

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

This function is useful if you need to call Builder.set_current_object to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want Builder.new_from_string instead.

Upon errors False will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_VARIANT_PARSE_ERROR domain.

It’s not really reasonable to attempt to handle failures of this call. The only reasonable thing to do when an error is detected is to call g_error().

Parameters:

buffer — the string to parse
length — the length of buffer (may be -1 if buffer is nul-terminated)

add_objects_from_file¶

def add_objects_from_file(self, filename: str | bytes | os.PathLike[str] | os.PathLike[bytes], object_ids: list[str]) -> bool

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

Upon errors, 0 will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_FILE_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a GtkTreeView that depends on its GtkTreeModel), you have to explicitly list all of them in object_ids.

Parameters:

filename — the name of the file to parse
object_ids — nul-terminated array of objects to build

add_objects_from_resource¶

def add_objects_from_resource(self, resource_path: str, object_ids: list[str]) -> bool

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

Upon errors, 0 will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_RESOURCE_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a GtkTreeView that depends on its GtkTreeModel), you have to explicitly list all of them in object_ids.

Parameters:

resource_path — the path of the resource file to parse
object_ids — nul-terminated array of objects to build

add_objects_from_string¶

def add_objects_from_string(self, buffer: str, length: int, object_ids: list[str]) -> bool

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

Upon errors False will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR or G_MARKUP_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a GtkTreeView that depends on its GtkTreeModel), you have to explicitly list all of them in object_ids.

Parameters:

buffer — the string to parse
length — the length of buffer (may be -1 if buffer is nul-terminated)
object_ids — nul-terminated array of objects to build

create_closure¶

def create_closure(self, function_name: str, flags: BuilderClosureFlags | int, object: GObject.Object | None = ...) -> GObject.Closure | None

Creates a closure to invoke the function called function_name.

This is using the create_closure() implementation of builder's BuilderScope.

If no closure could be created, None will be returned and error will be set.

Parameters:

function_name — name of the function to look up
flags — closure creation flags
object — Object to create the closure with

expose_object¶

def expose_object(self, name: str, object: GObject.Object) -> None

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

Only a single object may be added using name. However, it is not an error to expose the same object under multiple names. gtk_builder_get_object() may be used to determine if an object has already been added with name.

Parameters:

name — the name of the object exposed to the builder
object — the object to expose

extend_with_template¶

def extend_with_template(self, object: GObject.Object, template_type: type | GObject.Type, buffer: str, length: int) -> bool

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

Most likely you do not need to call this function in applications as templates are handled by GtkWidget.

Parameters:

object — the object that is being extended
template_type — the type that the template is for
buffer — the string to parse
length — the length of buffer (may be -1 if buffer is nul-terminated)

get_current_object¶

def get_current_object(self) -> GObject.Object | None

Gets the current object set via Builder.set_current_object.

get_object¶

def get_object(self, name: str) -> GObject.Object | None

Gets the object named name.

Note that this function does not increment the reference count of the returned object.

Parameters:

name — name of object to get

get_objects¶

def get_objects(self) -> list[GObject.Object]

Gets all objects that have been constructed by builder.

Note that this function does not increment the reference counts of the returned objects.

get_scope¶

def get_scope(self) -> BuilderScope

Gets the scope in use that was set via Builder.set_scope.

get_translation_domain¶

def get_translation_domain(self) -> str | None

Gets the translation domain of builder.

get_type_from_name¶

def get_type_from_name(self, type_name: str) -> type | GObject.Type

Looks up a type by name.

This is using the virtual function that GtkBuilder has for that purpose. This is mainly used when implementing the GtkBuildable interface on a type.

Parameters:

type_name — type name to lookup

set_current_object¶

def set_current_object(self, current_object: GObject.Object | None = ...) -> None

Sets the current object for the builder.

The current object can be thought of as the this object that the builder is working for and will often be used as the default object when an object is optional.

Widget.init_template for example will set the current object to the widget the template is inited for. For functions like Builder.new_from_resource, the current object will be None.

Parameters:

current_object — the new current object

set_scope¶

def set_scope(self, scope: BuilderScope | None = ...) -> None

Sets the scope the builder should operate in.

If scope is None, a new BuilderCScope will be created.

Parameters:

scope — the scope to use

set_translation_domain¶

def set_translation_domain(self, domain: str | None = ...) -> None

Sets the translation domain of builder.

Parameters:

domain — the translation domain

value_from_string¶

def value_from_string(self, pspec: GObject.ParamSpec, string: str) -> tuple[bool, GObject.Value]

Demarshals a value from a string.

This function calls GObject.Value.init on the value argument, so it need not be initialised beforehand.

Can handle char, uchar, boolean, int, uint, long, ulong, enum, flags, float, double, string, GdkRGBA and GtkAdjustment type values.

Upon errors False will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR domain.

Parameters:

pspec — the GParamSpec for the property
string — the string representation of the value

value_from_string_type¶

def value_from_string_type(self, type: type | GObject.Type, string: str) -> tuple[bool, GObject.Value]

Demarshals a value from a string.

Unlike Builder.value_from_string, this function takes a GType instead of GParamSpec.

Calls GObject.Value.init on the value argument, so it need not be initialised beforehand.

Upon errors False will be returned and error will be assigned a GError from the GTK_BUILDER_ERROR domain.

Parameters:

type — the GType of the value
string — the string representation of the value

Properties¶

current_object¶

current_object: GObject.Object  # read/write

The object the builder is evaluating for.

scope¶

scope: BuilderScope  # read/write

The scope the builder is operating in

translation_domain¶

translation_domain: str  # read/write

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

If the translation domain is None, GtkBuilder uses gettext(), otherwise GLib.dgettext.