Description

A Gnome::Gtk4::Builder reads XML descriptions of a user interface and instantiates the described objects.

To create a Gnome::Gtk4::Builder from a user interface description, call .new-from-file(), .new-from-resource() or .new-from-string().

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same Gnome::Gtk4::Builder you can call .newbuilder() to get an empty builder and populate it by (multiple) calls to .add-from-file(), .add-from-resource() or .add-from-string().

A Gnome::Gtk4::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 .destroy() in class Gnome::Gtk4::Window to get rid of them and all the widgets they contain.

The functions .get-object() and .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 .destroy() in class Gnome::Gtk4::Window. 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 g_object_ref() to keep them beyond the lifespan of the builder.

GtkBuilder UI Definitions

Gnome::Gtk4::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 .set-translation-domain() 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>`”. Gnome::Gtk4::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 Gnome::GObject::T-type()` 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 .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:

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:

Gnome::Gtk4::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”)

• colors (in a format understood by .parse() in class Gnome::Gdk4::N-RGBA)

• Gnome::Glib::N-Variant (can be specified in the format understood by .Variant.parse() in package Gnome::GLib)

• 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 .expose-object(). In general, Gnome::Gtk4::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 child defined in Gnome::Gtk4::Expander. 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 Gnome::Gtk4::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 Gnome::Gtk4::R-Buildable interface can specify how children may be added to it. Since many objects and widgets that are included with GTK already implement the Gnome::Gtk4::R-Buildable interface, typically child objects can be added using the `<child>` element without having to be concerned about the underlying implementation.

See the [Gnome::Gtk4::Widget documentation](class.Widget.html#gtkwidget-as-gtkbuildable) for many examples of using Gnome::Gtk4::Builder with widgets, including setting child objects using the `<child>` element.

A noteworthy special case to the general rule that only objects implementing Gnome::Gtk4::R-Buildable may specify how to handle the `<child>` element is that Gnome::Gtk4::Builder provides special support for adding objects to a Gnome::Gtk4::Builder 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, Gnome::Gtk4::Builder implements this using Gnome::Gtk4::Builder 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 .bind-property() in class Gnome::GObject::Object method.

Please note that another way to set up bindings between objects in .ui files is to use the Gnome::Gtk4::Expression methodology. See the [Gnome::Gtk4::Expression documentation](class.Expression.html#gtkexpression-in-ui-files) 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 Gnome::Gtk4::Dialog). This can be achieved by setting the “internal-child” property of the `<child>` element to a true value. Note that Gnome::Gtk4::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 .signal-connect-object() in package Gnome::GObject or .signal-connect-data() in package Gnome::GObject 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`.

Example UI Definition

Using GtkBuildable for extending UI definitions

Objects can implement the Gnome::Gtk4::R-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 Gnome::Gtk4::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 [Gnome::Gtk4::Widget documentation](class.Widget.html#building-composite-widgets-from-template-xml) for details.

Class initialization

new

:native-object

Create an object using a native object from elsewhere. See also Gnome::N::TopLevelSupportClass.

multi method new ( N-Object :$native-object! )

new-builder

Creates a new empty builder object.

This function is only useful if you intend to make multiple calls to .add-from-file(), .add-from-resource() or .add-from-string() in order to merge multiple UI descriptions into a single builder.

method new-builder ( --> Gnome::Gtk4::Builder \)

new-from-file

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.

method new-from-file ( Str $filename --> Gnome::Gtk4::Builder \)

• $filename; filename of user interface description file.

new-from-resource

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.

method new-from-resource ( Str $resource-path --> Gnome::Gtk4::Builder \)

• $resource-path; a Gnome::Gio::N-Resource resource path.

new-from-string

Parses the UI definition in $string.

If $string is undefined-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.

method new-from-string ( Str $string, Int() $length --> Gnome::Gtk4::Builder \)

• $string; a user interface (XML) description.

• $length; the length of $string, or -1.

Methods

add-from-file

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 .set-current-object()) to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want .new-from-file() instead.

If an error occurs, 0 will be returned and $error will be assigned a Gnome::Glib::N-Error 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 Gnome::Gtk4::Builder 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()`.

method add-from-file ( Str $filename, CArray[N-Error] $err --> Bool )

• $filename; the name of the file to parse.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

add-from-resource

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 .set-current-object() to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want .new-from-resource() instead.

If an error occurs, 0 will be returned and $error will be assigned a Gnome::Glib::N-Error 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().

method add-from-resource ( Str $resource-path, CArray[N-Error] $err --> Bool )

• $resource-path; the path of the resource file to parse.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

add-from-string

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 .set-current-object() to add user data to callbacks before loading Gnome::Gtk4::Builder UI. Otherwise, you probably want .new-from-string() instead.

Upon errors False will be returned and $error will be assigned a Gnome::Glib::N-Error 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().

method add-from-string ( Str $buffer, Int() $length, CArray[N-Error] $err --> Bool )

• $buffer; the string to parse.

• $length; the length of $buffer (may be -1 if $buffer is nul-terminated).

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

add-objects-from-file

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 Gnome::Glib::N-Error 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 Gnome::Gtk4::TreeView that depends on its Gnome::Gtk4::R-TreeModel), you have to explicitly list all of them in $object-ids.

method add-objects-from-file ( Str $filename, Array[Str] $object-ids, CArray[N-Error] $err --> Bool )

• $filename; the name of the file to parse.

• $object-ids; nul-terminated array of objects to build.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

add-objects-from-resource

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 Gnome::Glib::N-Error 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 Gnome::Gtk4::TreeView that depends on its Gnome::Gtk4::R-TreeModel), you have to explicitly list all of them in $object-ids.

method add-objects-from-resource ( Str $resource-path, Array[Str] $object-ids, CArray[N-Error] $err --> Bool )

• $resource-path; the path of the resource file to parse.

• $object-ids; nul-terminated array of objects to build.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

add-objects-from-string

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 Gnome::Glib::N-Error 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 Gnome::Gtk4::TreeView that depends on its Gnome::Gtk4::R-TreeModel), you have to explicitly list all of them in $object-ids.

method add-objects-from-string ( Str $buffer, Int() $length, Array[Str] $object-ids, CArray[N-Error] $err --> Bool )

• $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.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success, False if an error occurred.

create-closure This function is not yet available

Creates a closure to invoke the function called $function-name.

This is using the create_closure() implementation of $builder's Gnome::Gtk4::R-BuilderScope.

If no closure could be created, undefined will be returned and $error will be set.

method create-closure ( Str $function-name, UInt $flags, N-Object() $object, CArray[N-Error] $err --> N-Object )

• $function-name; name of the function to look up.

• $flags; closure creation flags.

• $object; Object to create the closure with.

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; A new closure for invoking $function-name.

expose-object

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. C<.get-object()>` may be used to determine if an object has already been added with $name.

method expose-object ( Str $name, N-Object() $object )

• $name; the name of the object exposed to the builder.

• $object; the object to expose.

extend-with-template

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 Gnome::Gtk4::Widget.

method extend-with-template ( N-Object() $object, GType $template-type, Str $buffer, Int() $length, CArray[N-Error] $err --> Bool )

• $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).

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; A positive value on success, 0 if an error occurred.

get-current-object

Gets the current object set via .set-current-object().

method get-current-object (--> N-Object )

Return value; the current object.

get-object

Gets the object named $name.

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

method get-object ( Str $name --> N-Object )

• $name; name of object to get.

Return value; the object named $name.

get-objects

Gets all objects that have been constructed by $builder.

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

method get-objects (--> N-SList )

Return value; a newly-allocated Gnome::Glib::N-SList containing all the objects constructed by the Gnome::Gtk4::Builder instance`. It should be freed by g_slist_free().

get-scope

Gets the scope in use that was set via .set-scope().

method get-scope (--> N-Object )

Return value; the current scope.

get-translation-domain

Gets the translation domain of $builder.

method get-translation-domain (--> Str )

Return value; the translation domain.

get-type-from-name

Looks up a type by name.

This is using the virtual function that Gnome::Gtk4::Builder has for that purpose. This is mainly used when implementing the Gnome::Gtk4::R-Buildable interface on a type.

method get-type-from-name ( Str $type-name --> GType )

• $type-name; type name to lookup.

Return value; the Gnome::GObject::Builder found for $type-name or G_TYPE_INVALID if no type was found.

set-current-object

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.

.init-template() in class Gnome::Gtk4::Widget for example will set the current object to the widget the template is inited for. For functions like .new-from-resource(), the current object will be undefined.

method set-current-object ( N-Object() $current-object )

• $current-object; the new current object.

set-scope

Sets the scope the builder should operate in.

If $scope is undefined, a new Gnome::Gtk4::BuilderCScope will be created.

method set-scope ( N-Object() $scope )

• $scope; the scope to use.

set-translation-domain

Sets the translation domain of $builder.

method set-translation-domain ( Str $domain )

• $domain; the translation domain.

value-from-string

Demarshals a value from a string.

This function calls g_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, Gnome::Gdk4::N-RGBA and Gnome::Gtk4::Adjustment type values.

Upon errors False will be returned and $error will be assigned a Gnome::Glib::N-Error from the GTK_BUILDER_ERROR domain.

method value-from-string ( N-Object() $pspec, Str $string, N-Object $value, CArray[N-Error] $err --> Bool )

• $pspec; the Gnome::GObject::ParamSpec for the property.

• $string; the string representation of the value.

• $value; the Gnome::GObject::N-Value to store the result in

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success.

value-from-string-type

Demarshals a value from a string.

Unlike .value-from-string(), this function takes a Gnome::GObject::Builder instead of Gnome::GObject::ParamSpec.

Calls g_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 Gnome::Glib::N-Error from the GTK_BUILDER_ERROR domain.

method value-from-string-type ( GType $type, Str $string, N-Object $value, CArray[N-Error] $err --> Bool )

• $type; the Gnome::GObject::Builder of the value.

• $string; the string representation of the value.

• $value; the Gnome::GObject::N-Value to store the result in

• $err; Error object. When defined, an error can be returned when there is one. Use Pointer when you want to ignore the error. .

Return value; True on success.