Struct Builder

pub struct Builder { /* private fields */ }

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

To create a Builder from a user interface description, call from_file(), from_resource() or from_string().

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same Builder you can call new() to get an empty builder and populate it by (multiple) calls to add_from_file(), add_from_resource() or add_from_string().

A 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::destroy() to get rid of them and all the widgets they contain.

The functions object() and 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 Gtk::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 g_object_ref() to keep them beyond the lifespan of the builder.

GtkBuilder UI Definitions

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:

<?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>”. Builder 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 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">Hello, world</property>
</object>

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 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 a format understood by gdk::RGBA::parse())
• GVariant (can be specified in the format understood by GLib::Variant::parse())
• 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 CWD if add_from_string() was used)
• GFile (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 CWD if 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 expose_object(). In general, 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. 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 Buildable interface, typically child objects can be added using the <child> element without having to be concerned about the underlying implementation.

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

A noteworthy special case to the general rule that only objects implementing Buildable may specify how to handle the <child> element is that Builder 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, Builder 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 ObjectExt::bind_property() method.

Please note that another way to set up bindings between objects in .ui files is to use the Expression methodology. See the [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 Dialog). This can be achieved by setting the “internal-child” property of the <child> element to a true value. Note that 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.

<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 signal_connect_object() or 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:

⚠️ The following code is in c ⚠️

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.

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 [Widget documentation](class.Widget.html#building-composite-widgets-from-template-xml) for details.

Properties

current-object

The object the builder is evaluating for.

Readable | Writeable

scope

The scope the builder is operating in

Readable | Writeable | Construct

translation-domain

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

If the translation domain is None, Builder uses gettext(), otherwise g_dgettext().

Readable | Writeable

Implements

[trait@glib::ObjectExt]

GLib type: GObject with reference counted clone semantics.

Implementations

impl Builder

pub fn 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.

Returns

a new (empty) Builder object

pub fn from_resource(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.

resource_path

a GResource resource path

Returns

a Builder containing the described interface

pub fn from_string(string: &str) -> 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.

string

a user interface (XML) description

length

the length of @string, or -1

Returns

a Builder containing the interface described by @string

pub fn add_from_resource(&self, resource_path: &str) -> Result<(), Error>

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

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 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().

resource_path

the path of the resource file to parse

Returns

true on success, false if an error occurred

pub fn add_from_string(&self, buffer: &str) -> Result<(), Error>

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

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

buffer

the string to parse

length

the length of @buffer (may be -1 if @buffer is nul-terminated)

Returns

true on success, false if an error occurred

pub fn add_objects_from_file( &self, filename: impl AsRef<Path>, object_ids: &[&str], ) -> Result<(), Error>

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

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 TreeView that depends on its TreeModel), you have to explicitly list all of them in @object_ids.

filename

the name of the file to parse

object_ids

nul-terminated array of objects to build

Returns

true on success, false if an error occurred

pub fn add_objects_from_resource( &self, resource_path: &str, object_ids: &[&str], ) -> Result<(), Error>

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

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 TreeView that depends on its TreeModel), you have to explicitly list all of them in @object_ids.

resource_path

the path of the resource file to parse

object_ids

nul-terminated array of objects to build

Returns

true on success, false if an error occurred

pub fn add_objects_from_string( &self, buffer: &str, object_ids: &[&str], ) -> Result<(), Error>

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

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 TreeView that depends on its TreeModel), you have to explicitly list all of them in @object_ids.

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

Returns

true on success, false if an error occurred

pub fn create_closure( &self, function_name: &str, flags: BuilderClosureFlags, object: Option<&impl IsA<Object>>, ) -> Result<Option<Closure>, Error>

Creates a closure to invoke the function called @function_name.

This is using the create_closure() implementation of @self’s BuilderScope.

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

function_name

name of the function to look up

flags

closure creation flags

object

Object to create the closure with

Returns

A new closure for invoking @function_name

pub fn expose_object(&self, name: &str, object: &impl IsA<Object>)

Add @object to the @self 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.

name

the name of the object exposed to the builder

object

the object to expose

pub fn extend_with_template( &self, object: &impl IsA<Object>, template_type: Type, buffer: &str, ) -> Result<(), Error>

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 Widget.

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)

Returns

A positive value on success, 0 if an error occurred

pub fn objects(&self) -> Vec<Object>

Gets all objects that have been constructed by @self.

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

Returns

a newly-allocated GSList containing all the objects constructed by the GtkBuilder instance. It should be freed by g_slist_free()

pub fn scope(&self) -> BuilderScope

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

Returns

the current scope

pub fn translation_domain(&self) -> Option<GString>

Gets the translation domain of @self.

Returns

the translation domain

pub fn type_from_name(&self, type_name: &str) -> Type

Looks up a type by name.

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

type_name

type name to lookup

Returns

the GType found for @type_name or G_TYPE_INVALID if no type was found

pub fn set_current_object(&self, current_object: Option<&impl IsA<Object>>)

Sets the current object for the @self.

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.

Gtk::Widget::init_template() for example will set the current object to the widget the template is inited for. For functions like from_resource(), the current object will be None.

current_object

the new current object

pub fn set_scope(&self, scope: Option<&impl IsA<BuilderScope>>)

Sets the scope the builder should operate in.

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

scope

the scope to use

pub fn set_translation_domain(&self, domain: Option<&str>)

Sets the translation domain of @self.

domain

the translation domain

pub fn value_from_string( &self, pspec: impl AsRef<ParamSpec>, string: &str, ) -> Result<Value, Error>

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, gdk::RGBA and Adjustment type values.

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

pspec

the GParamSpec for the property

string

the string representation of the value

Returns

true on success

value

the GValue to store the result in

pub fn value_from_string_type( &self, type_: Type, string: &str, ) -> Result<Value, Error>

Demarshals a value from a string.

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

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 GError from the GTK_BUILDER_ERROR domain.

type_

the GType of the value

string

the string representation of the value

Returns

true on success

value

the GValue to store the result in

pub fn connect_current_object_notify<F: Fn(&Self) + 'static>( &self, f: F, ) -> SignalHandlerId

pub fn connect_scope_notify<F: Fn(&Self) + 'static>( &self, f: F, ) -> SignalHandlerId

pub fn connect_translation_domain_notify<F: Fn(&Self) + 'static>( &self, f: F, ) -> SignalHandlerId

impl Builder

pub fn from_file(file_path: impl AsRef<Path>) -> Self

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.

filename

filename of user interface description file

Returns

a Builder containing the described interface

pub fn current_object(&self) -> Option<Object>

Gets the current object set via gtk_builder_set_current_object().

Returns

the current object

pub fn object<T: IsA<Object>>(&self, name: impl IntoGStr) -> Option<T>

Gets the object named @name.

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

name

name of object to get

Returns

the object named @name

pub fn add_from_file(&self, file_path: impl AsRef<Path>) -> Result<(), Error>

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

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 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 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().

filename

the name of the file to parse

Returns

true on success, false if an error occurred

Trait Implementations

impl Clone for Builder

fn clone(&self) -> Self

Makes a clone of this shared reference.

This increments the strong reference count of the object. Dropping the object will decrement it again.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Builder

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Builder

fn default() -> Self

Returns the “default value” for a type.

impl HasParamSpec for Builder

type ParamSpec = ParamSpecObject

type SetValue = Builder

Preferred value to be used as setter for the associated ParamSpec.

type BuilderFn = fn(_: &str) -> ParamSpecObjectBuilder<'_, Builder>

fn param_spec_builder() -> Self::BuilderFn

impl Hash for Builder

fn hash<H>(&self, state: &mut H)

where H: Hasher,

Hashes the memory address of this object.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Builder

fn cmp(&self, other: &Self) -> Ordering

Comparison for two GObjects.

Compares the memory addresses of the provided objects.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl ParentClassIs for Builder

type Parent = Object

impl<OT: ObjectType> PartialEq<OT> for Builder

fn eq(&self, other: &OT) -> bool

Equality for two GObjects.

Two GObjects are equal if their memory addresses are equal.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<OT: ObjectType> PartialOrd<OT> for Builder

fn partial_cmp(&self, other: &OT) -> Option<Ordering>

Partial comparison for two GObjects.

Compares the memory addresses of the provided objects.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StaticType for Builder

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for Builder