GBinding: GObject Reference Manual

GBinding

GBinding — Bind two object properties

Functions

GObject *	g_binding_get_source ()
const gchar *	g_binding_get_source_property ()
GObject *	g_binding_get_target ()
const gchar *	g_binding_get_target_property ()
GBindingFlags	g_binding_get_flags ()
void	g_binding_unbind ()
GBinding *	g_object_bind_property ()
gboolean	(*GBindingTransformFunc) ()
GBinding *	g_object_bind_property_full ()
GBinding *	g_object_bind_property_with_closures ()

Properties

GBindingFlags	flags	Read / Write / Construct Only
GObject *	source	Read / Write / Construct Only
gchar *	source-property	Read / Write / Construct Only
GObject *	target	Read / Write / Construct Only
gchar *	target-property	Read / Write / Construct Only

Types and Values

	GBinding
enum	GBindingFlags

Object Hierarchy

    GObject
    ╰── GBinding

Includes

#include <glib-object.h>

Description

GBinding is the representation of a binding between a property on a GObject instance (or source) and another property on another GObject instance (or target). Whenever the source property changes, the same value is applied to the target property; for instance, the following binding:

1
2
3

g_object_bind_property (object1, "property-a",
                        object2, "property-b",
                        G_BINDING_DEFAULT);

will cause the property named "property-b" of object2 to be updated every time g_object_set() or the specific accessor changes the value of the property "property-a" of object1 .

It is possible to create a bidirectional binding between two properties of two GObject instances, so that if either property changes, the other is updated as well, for instance:

1
2
3

g_object_bind_property (object1, "property-a",
                        object2, "property-b",
                        G_BINDING_BIDIRECTIONAL);

will keep the two properties in sync.

It is also possible to set a custom transformation function (in both directions, in case of a bidirectional binding) to apply a custom transformation from the source value to the target value before applying it; for instance, the following binding:

g_object_bind_property_full (adjustment1, "value",
                             adjustment2, "value",
                             G_BINDING_BIDIRECTIONAL,
                             celsius_to_fahrenheit,
                             fahrenheit_to_celsius,
                             NULL, NULL);

will keep the "value" property of the two adjustments in sync; the celsius_to_fahrenheit function will be called whenever the "value" property of adjustment1 changes and will transform the current value of the property before applying it to the "value" property of adjustment2 .

Vice versa, the fahrenheit_to_celsius function will be called whenever the "value" property of adjustment2 changes, and will transform the current value of the property before applying it to the "value" property of adjustment1 .

Note that GBinding does not resolve cycles by itself; a cycle like

1
2
3

object1:propertyA -> object2:propertyB
object2:propertyB -> object3:propertyC
object3:propertyC -> object1:propertyA

might lead to an infinite loop. The loop, in this particular case, can be avoided if the objects emit the “notify” signal only if the value has effectively been changed. A binding is implemented using the “notify” signal, so it is susceptible to all the various ways of blocking a signal emission, like g_signal_stop_emission() or g_signal_handler_block().

A binding will be severed, and the resources it allocates freed, whenever either one of the GObject instances it refers to are finalized, or when the GBinding instance loses its last reference.

Bindings for languages with garbage collection can use g_binding_unbind() to explicitly release a binding between the source and target properties, instead of relying on the last reference on the binding, source, and target instances to drop.

GBinding is available since GObject 2.26

Functions

g_binding_get_source ()

GObject *
g_binding_get_source (GBinding *binding);

Retrieves the GObject instance used as the source of the binding.

Parameters

binding

a GBinding

Returns

the source GObject.

[transfer none]

Since: 2.26

g_binding_get_source_property ()

const gchar *
g_binding_get_source_property (GBinding *binding);

Retrieves the name of the property of “source” used as the source of the binding.

Parameters

binding

a GBinding

Returns

the name of the source property

Since: 2.26

g_binding_get_target ()

GObject *
g_binding_get_target (GBinding *binding);

Retrieves the GObject instance used as the target of the binding.

Parameters

binding

a GBinding

Returns

the target GObject.

[transfer none]

Since: 2.26

g_binding_get_target_property ()

const gchar *
g_binding_get_target_property (GBinding *binding);

Retrieves the name of the property of “target” used as the target of the binding.

Parameters

binding

a GBinding

Returns

the name of the target property

Since: 2.26

g_binding_get_flags ()

GBindingFlags
g_binding_get_flags (GBinding *binding);

Retrieves the flags passed when constructing the GBinding.

Parameters

binding

a GBinding

Returns

the GBindingFlags used by the GBinding

Since: 2.26

g_binding_unbind ()

void
g_binding_unbind (GBinding *binding);

Explicitly releases the binding between the source and the target property expressed by binding .

This function will release the reference that is being held on the binding instance; if you want to hold on to the GBinding instance after calling g_binding_unbind(), you will need to hold a reference to it.

Parameters

binding

a GBinding

Since: 2.38

g_object_bind_property ()

GBinding *
g_object_bind_property (gpointer source,
                        const gchar *source_property,
                        gpointer target,
                        const gchar *target_property,
                        GBindingFlags flags);

Creates a binding between source_property on source and target_property on target . Whenever the source_property is changed the target_property is updated using the same value. For instance:

1	g_object_bind_property (action, "active", widget, "sensitive", 0);

Will result in the "sensitive" property of the widget GObject instance to be updated with the same value of the "active" property of the action GObject instance.

If flags contains G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well.

The binding will automatically be removed when either the source or the target instances are finalized. To remove the binding without affecting the source and the target you can just call g_object_unref() on the returned GBinding instance.

A GObject can have multiple bindings.

Parameters

source	the source GObject.	[type GObject.Object]
source_property	the property on `source` to bind
target	the target GObject.	[type GObject.Object]
target_property	the property on `target` to bind
flags	flags to pass to GBinding

Returns

the GBinding instance representing the binding between the two GObject instances. The binding is released whenever the GBinding reference count reaches zero.

[transfer none]

Since: 2.26

GBindingTransformFunc ()

gboolean
(*GBindingTransformFunc) (GBinding *binding,
                          const GValue *from_value,
                          GValue *to_value,
                          gpointer user_data);

A function to be called to transform from_value to to_value . If this is the transform_to function of a binding, then from_value is the source_property on the source object, and to_value is the target_property on the target object. If this is the transform_from function of a G_BINDING_BIDIRECTIONAL binding, then those roles are reversed.

Parameters

binding	a GBinding
from_value	the GValue containing the value to transform
to_value	the GValue in which to store the transformed value
user_data	data passed to the transform function

Returns

TRUE if the transformation was successful, and FALSE otherwise

Since: 2.26

g_object_bind_property_full ()

GBinding *
g_object_bind_property_full (gpointer source,
                             const gchar *source_property,
                             gpointer target,
                             const gchar *target_property,
                             GBindingFlags flags,
                             GBindingTransformFunc transform_to,
                             GBindingTransformFunc transform_from,
                             gpointer user_data,
                             GDestroyNotify notify);

Complete version of g_object_bind_property().

Creates a binding between source_property on source and target_property on target , allowing you to set the transformation functions to be used by the binding.

If flags contains G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well. The transform_from function is only used in case of bidirectional bindings, otherwise it will be ignored

A GObject can have multiple bindings.

The same user_data parameter will be used for both transform_to and transform_from transformation functions; the notify function will be called once, when the binding is removed. If you need different data for each transformation function, please use g_object_bind_property_with_closures() instead.

Parameters

source	the source GObject.	[type GObject.Object]
source_property	the property on `source` to bind
target	the target GObject.	[type GObject.Object]
target_property	the property on `target` to bind
flags	flags to pass to GBinding
transform_to	the transformation function from the `source` to the `target` , or `NULL` to use the default.	[scope notified][allow-none]
transform_from	the transformation function from the `target` to the `source` , or `NULL` to use the default.	[scope notified][allow-none]
user_data	custom data to be passed to the transformation functions, or `NULL`
notify	function to be called when disposing the binding, to free the resources used by the transformation functions

Returns

the GBinding instance representing the binding between the two GObject instances. The binding is released whenever the GBinding reference count reaches zero.

[transfer none]

Since: 2.26

g_object_bind_property_with_closures ()

GBinding *
g_object_bind_property_with_closures (gpointer source,
                                      const gchar *source_property,
                                      gpointer target,
                                      const gchar *target_property,
                                      GBindingFlags flags,
                                      GClosure *transform_to,
                                      GClosure *transform_from);

Creates a binding between source_property on source and target_property on target , allowing you to set the transformation functions to be used by the binding.

This function is the language bindings friendly version of g_object_bind_property_full(), using GClosures instead of function pointers.

[rename-to g_object_bind_property_full]

Parameters

source	the source GObject.	[type GObject.Object]
source_property	the property on `source` to bind
target	the target GObject.	[type GObject.Object]
target_property	the property on `target` to bind
flags	flags to pass to GBinding
transform_to	a GClosure wrapping the transformation function from the `source` to the `target` , or `NULL` to use the default
transform_from	a GClosure wrapping the transformation function from the `target` to the `source` , or `NULL` to use the default

Returns

the GBinding instance representing the binding between the two GObject instances. The binding is released whenever the GBinding reference count reaches zero.

[transfer none]

Since: 2.26

Types and Values

GBinding

typedef struct _GBinding GBinding;

GBinding is an opaque structure whose members cannot be accessed directly.

Since: 2.26

enum GBindingFlags

Flags to be passed to g_object_bind_property() or g_object_bind_property_full().

This enumeration can be extended at later date.

Members

G_BINDING_DEFAULT	The default binding; if the source property changes, the target property is updated with its value.
G_BINDING_BIDIRECTIONAL	Bidirectional binding; if either the property of the source or the property of the target changes, the other is updated.
G_BINDING_SYNC_CREATE	Synchronize the values of the source and target properties when creating the binding; the direction of the synchronization is always from the source to the target.
G_BINDING_INVERT_BOOLEAN	If the two properties being bound are booleans, setting one to `TRUE` will result in the other being set to `FALSE` and vice versa. This flag will only work for boolean properties, and cannot be used when passing custom transformation functions to `g_object_bind_property_full()`.

Since: 2.26