A gtk.builder.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.window.Window.destroy to get rid of them and all the widgets
they contain.
The functions gtk.builder.Builder.getObject and
gtk.builder.Builder.getObjects 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.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.ObjectG.ref_ to keep them beyond the lifespan of the builder.
gtk.builder.Builder 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.Builder.setTranslationDomain on the builder.
For example:
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>”. gtk.builder.Builder will
error out if the version requirements are not met. For example:
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
[gobject.global.typeEnsure] 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
gtk.builder.Builder.getObject. 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:
gtk.builder.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 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, e.g.
“GTK_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE”, or “emoji|lowercase”)
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.Builder.exposeObject. In general, gtk.builder.Builder 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.
Many widgets have properties for child widgets, such as
gtk.expander.Expander.Widget. In this case, the preferred way to
specify the child widget in a ui file is to simply set the property:
Generic containers that can contain an arbitrary number of children,
such as gtk.box.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 gtk.buildable.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.Buildable interface,
typically child objects can be added using the <child> element without
having to be concerned about the underlying implementation.
A noteworthy special case to the general rule that only objects implementing
gtk.buildable.Buildable may specify how to handle the <child> element is that
gtk.builder.Builder provides special support for adding objects to a
gio.list_store.ListStore by using the <child> element. For instance:
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, gtk.builder.Builder implements this using
gobject.binding.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:
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 gtk.dialog.Dialog). This can be achieved by setting the “internal-child”
property of the <child> element to a true value. Note that gtk.builder.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.
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
func@GObject.signal_connect_object or func@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:
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.
Objects can implement the gtk.buildable.Buildable interface to add custom
elements and attributes to the XML. Typically, any extension will be
documented in each type that implements the interface.
When describing a gtk.widget.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.
A gtk.builder.Builder reads XML descriptions of a user interface and instantiates the described objects.
To create a gtk.builder.Builder from a user interface description, call gtk.builder.Builder.newFromFile, gtk.builder.Builder.newFromResource or gtk.builder.Builder.newFromString.
In the (unusual) case that you want to add user interface descriptions from multiple sources to the same gtk.builder.Builder you can call gtk.builder.Builder.new_ to get an empty builder and populate it by (multiple) calls to gtk.builder.Builder.addFromFile, gtk.builder.Builder.addFromResource or gtk.builder.Builder.addFromString.
A gtk.builder.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.window.Window.destroy to get rid of them and all the widgets they contain.
The functions gtk.builder.Builder.getObject and gtk.builder.Builder.getObjects 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.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.ObjectG.ref_ to keep them beyond the lifespan of the builder.
GtkBuilder UI Definitions
gtk.builder.Builder 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 gtk.builder.Builder.setTranslationDomain on the builder. For example:
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>”. gtk.builder.Builder will error out if the version requirements are not met. For example:
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 [gobject.global.typeEnsure] 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 gtk.builder.Builder.getObject. 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:
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.Builder can parse textual representations for the most common property types:
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.Builder.exposeObject. In general, gtk.builder.Builder 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 gtk.expander.Expander.Widget. In this case, the preferred way to specify the child widget in a ui file is to simply set the property:
Generic containers that can contain an arbitrary number of children, such as gtk.box.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 gtk.buildable.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.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.Widget] documentation for many examples of using gtk.builder.Builder with widgets, including setting child objects using the <child> element.
A noteworthy special case to the general rule that only objects implementing gtk.buildable.Buildable may specify how to handle the <child> element is that gtk.builder.Builder provides special support for adding objects to a gio.list_store.ListStore by using the <child> element. For instance:
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, gtk.builder.Builder implements this using gobject.binding.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:
For more information, see the documentation of the gobject.object.ObjectG.bindProperty method.
Please note that another way to set up bindings between objects in .ui files is to use the gtk.expression.Expression methodology. See the [gtk.expression.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 (e.g. the content area of a gtk.dialog.Dialog). This can be achieved by setting the “internal-child” property of the <child> element to a true value. Note that gtk.builder.Builder 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.
The remaining attributes, “after”, “swapped” and “object”, have the same meaning as the corresponding parameters of the func@GObject.signal_connect_object or func@GObject.signal_connect_data functions:
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:
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
Using GtkBuildable for extending UI definitions
Objects can implement the gtk.buildable.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.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 [gtk.widget.Widget] documentation for details.