GObject

typedef struct _GObject GObject;

All the fields in the GObject structure are private to the GObject implementation and should never be accessed directly.

GObjectClass

typedef struct {
  GTypeClass   g_type_class;

  /* seldomly overidden */
  GObject*   (*constructor)     (GType                  type,
                                 guint                  n_construct_properties,
                                 GObjectConstructParam *construct_properties);
  /* overridable methods */
  void       (*set_property)		(GObject        *object,
                                         guint           property_id,
                                         const GValue   *value,
                                         GParamSpec     *pspec);
  void       (*get_property)		(GObject        *object,
                                         guint           property_id,
                                         GValue         *value,
                                         GParamSpec     *pspec);
  void       (*dispose)			(GObject        *object);
  void       (*finalize)		(GObject        *object);
  /* seldomly overidden */
  void       (*dispatch_properties_changed) (GObject      *object,
					     guint	   n_pspecs,
					     GParamSpec  **pspecs);
  /* signals */
  void	     (*notify)			(GObject	*object,
					 GParamSpec	*pspec);

  /* called when done constructing */
  void	     (*constructed)		(GObject	*object);
} GObjectClass;

The class structure for the GObject type.

static MySingleton *the_singleton = NULL;

static GObject*
my_singleton_constructor (GType                  type,
                          guint                  n_construct_params,
                          GObjectConstructParam *construct_params)
{
  GObject *object;
  
  if (!the_singleton)
    {
      object = G_OBJECT_CLASS (parent_class)->constructor (type,
                                                           n_construct_params,
                                                           construct_params);
      the_singleton = MY_SINGLETON (object);
    }
  else
    object = g_object_ref (G_OBJECT (the_singleton));

  return object;
}

GObjectConstructParam

typedef struct {
  GParamSpec *pspec;
  GValue     *value;
} GObjectConstructParam;

The GObjectConstructParam struct is an auxiliary structure used to hand GParamSpec/GValue pairs to the constructor of a GObjectClass.

GObjectGetPropertyFunc ()

void                (*GObjectGetPropertyFunc)           (GObject *object,
                                                         guint property_id,
                                                         GValue *value,
                                                         GParamSpec *pspec);

The type of the get_property function of GObjectClass.

GObjectSetPropertyFunc ()

void                (*GObjectSetPropertyFunc)           (GObject *object,
                                                         guint property_id,
                                                         const GValue *value,
                                                         GParamSpec *pspec);

The type of the set_property function of GObjectClass.

GObjectFinalizeFunc ()

void                (*GObjectFinalizeFunc)              (GObject *object);

The type of the finalize function of GObjectClass.

G_TYPE_IS_OBJECT()

#define G_TYPE_IS_OBJECT(type)      (G_TYPE_FUNDAMENTAL (type) == G_TYPE_OBJECT)

Returns a boolean value of FALSE or TRUE indicating whether the passed in type id is a G_TYPE_OBJECT or derived from it.

G_OBJECT()

#define G_OBJECT(object)            (G_TYPE_CHECK_INSTANCE_CAST ((object), G_TYPE_OBJECT, GObject))

Casts a GObject or derived pointer into a (GObject*) pointer. Depending on the current debugging level, this function may invoke certain runtime checks to identify invalid casts.

G_IS_OBJECT()

#define G_IS_OBJECT(object)         (G_TYPE_CHECK_INSTANCE_TYPE ((object), G_TYPE_OBJECT))

Checks whether a valid GTypeInstance pointer is of type G_TYPE_OBJECT.

G_OBJECT_CLASS()

#define G_OBJECT_CLASS(class)       (G_TYPE_CHECK_CLASS_CAST ((class), G_TYPE_OBJECT, GObjectClass))

Casts a derived GObjectClass structure into a GObjectClass structure.

G_IS_OBJECT_CLASS()

#define G_IS_OBJECT_CLASS(class)    (G_TYPE_CHECK_CLASS_TYPE ((class), G_TYPE_OBJECT))

Checks whether class "is a" valid GObjectClass structure of type G_TYPE_OBJECT or derived.

G_OBJECT_GET_CLASS()

#define G_OBJECT_GET_CLASS(object)  (G_TYPE_INSTANCE_GET_CLASS ((object), G_TYPE_OBJECT, GObjectClass))

Returns the class structure associated to a GObject instance.

G_OBJECT_TYPE()

#define G_OBJECT_TYPE(object)       (G_TYPE_FROM_INSTANCE (object))

Return the type id of an object.

G_OBJECT_TYPE_NAME()

#define G_OBJECT_TYPE_NAME(object)  (g_type_name (G_OBJECT_TYPE (object)))

Returns the name of an object's type.

G_OBJECT_CLASS_TYPE()

#define G_OBJECT_CLASS_TYPE(class)  (G_TYPE_FROM_CLASS (class))

Return the type id of a class structure.

G_OBJECT_CLASS_NAME()

#define G_OBJECT_CLASS_NAME(class)  (g_type_name (G_OBJECT_CLASS_TYPE (class)))

Return the name of a class structure's type.

g_object_class_install_property ()

void                g_object_class_install_property     (GObjectClass *oclass,
                                                         guint property_id,
                                                         GParamSpec *pspec);

Installs a new property. This is usually done in the class initializer.

g_object_class_find_property ()

GParamSpec*         g_object_class_find_property        (GObjectClass *oclass,
                                                         const gchar *property_name);

Looks up the GParamSpec for a property of a class.

g_object_class_list_properties ()

GParamSpec**        g_object_class_list_properties      (GObjectClass *oclass,
                                                         guint *n_properties);

Returns an array of GParamSpec* for all properties of a class.

g_object_class_override_property ()

void                g_object_class_override_property    (GObjectClass *oclass,
                                                         guint property_id,
                                                         const gchar *name);

Registers property_id as referring to a property with the name name in a parent class or in an interface implemented by oclass. This allows this class to override a property implementation in a parent class or to provide the implementation of a property from an interface.

Since 2.4

g_object_interface_install_property ()

void                g_object_interface_install_property (gpointer g_iface,
                                                         GParamSpec *pspec);

Add a property to an interface; this is only useful for interfaces that are added to GObject-derived types. Adding a property to an interface forces all objects classes with that interface to have a compatible property. The compatible property could be a newly created GParamSpec, but normally g_object_class_override_property() will be used so that the object class only needs to provide an implementation and inherits the property description, default value, bounds, and so forth from the interface property.

This function is meant to be called from the interface's default vtable initialization function (the class_init member of GTypeInfo.) It must not be called after after class_init has been called for any object types implementing this interface.

Since 2.4

g_object_interface_find_property ()

GParamSpec*         g_object_interface_find_property    (gpointer g_iface,
                                                         const gchar *property_name);

Find the GParamSpec with the given name for an interface. Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

Since 2.4

g_object_interface_list_properties ()

GParamSpec**        g_object_interface_list_properties  (gpointer g_iface,
                                                         guint *n_properties_p);

Lists the properties of an interface.Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

Since 2.4

g_object_new ()

gpointer            g_object_new                        (GType object_type,
                                                         const gchar *first_property_name,
                                                         ...);

Creates a new instance of a GObject subtype and sets its properties.

Construction parameters (see G_PARAM_CONSTRUCT, G_PARAM_CONSTRUCT_ONLY) which are not explicitly specified are set to their default values.

g_object_newv ()

gpointer            g_object_newv                       (GType object_type,
                                                         guint n_parameters,
                                                         GParameter *parameters);

Creates a new instance of a GObject subtype and sets its properties.

Construction parameters (see G_PARAM_CONSTRUCT, G_PARAM_CONSTRUCT_ONLY) which are not explicitly specified are set to their default values.

GParameter

typedef struct {
  const gchar *name;
  GValue       value;
} GParameter;

The GParameter struct is an auxiliary structure used to hand parameter name/value pairs to g_object_newv().

g_object_ref ()

gpointer            g_object_ref                        (gpointer object);

Increases the reference count of object.

g_object_unref ()

void                g_object_unref                      (gpointer object);

Decreases the reference count of object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).

g_object_ref_sink ()

gpointer            g_object_ref_sink                   (gpointer object);

Increase the reference count of object, and possibly remove the floating reference, if object has a floating reference.

In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

Since 2.10

GInitiallyUnowned

typedef struct _GObject                  GInitiallyUnowned;

All the fields in the GInitiallyUnowned structure are private to the GInitiallyUnowned implementation and should never be accessed directly.

GInitiallyUnownedClass

typedef struct _GObjectClass             GInitiallyUnownedClass;

The class structure for the GInitiallyUnowned type.

G_TYPE_INITIALLY_UNOWNED

#define G_TYPE_INITIALLY_UNOWNED	      (g_initially_unowned_get_type())

The type for GInitiallyUnowned.

g_object_is_floating ()

gboolean            g_object_is_floating                (gpointer object);

Checks wether object has a floating reference.

Since 2.10

g_object_force_floating ()

void                g_object_force_floating             (GObject *object);

This function is intended for GObject implementations to re-enforce a floating object reference. Doing this is seldomly required, all GInitiallyUnowneds are created with a floating reference which usually just needs to be sunken by calling g_object_ref_sink().

Since 2.10

GWeakNotify ()

void                (*GWeakNotify)                      (gpointer data,
                                                         GObject *where_the_object_was);

A GWeakNotify function can be added to an object as a callback that gets triggered when the object is finalized. Since the object is already being finalized when the GWeakNotify is called, there's not much you could do with the object, apart from e.g. using its adress as hash-index or the like.

g_object_weak_ref ()

void                g_object_weak_ref                   (GObject *object,
                                                         GWeakNotify notify,
                                                         gpointer data);

Adds a weak reference callback to an object. Weak references are used for notification when an object is finalized. They are called "weak references" because they allow you to safely hold a pointer to an object without calling g_object_ref() (g_object_ref() adds a strong reference, that is, forces the object to stay alive).

g_object_weak_unref ()

void                g_object_weak_unref                 (GObject *object,
                                                         GWeakNotify notify,
                                                         gpointer data);

Removes a weak reference callback to an object.

g_object_add_weak_pointer ()

void                g_object_add_weak_pointer           (GObject *object,
                                                         gpointer *weak_pointer_location);

Adds a weak reference from weak_pointer to object to indicate that the pointer located at weak_pointer_location is only valid during the lifetime of object. When the object is finalized, weak_pointer will be set to NULL.

g_object_remove_weak_pointer ()

void                g_object_remove_weak_pointer        (GObject *object,
                                                         gpointer *weak_pointer_location);

Removes a weak reference from object that was previously added using g_object_add_weak_pointer(). The weak_pointer_location has to match the one used with g_object_add_weak_pointer().

GToggleNotify ()

void                (*GToggleNotify)                    (gpointer data,
                                                         GObject *object,
                                                         gboolean is_last_ref);

A callback function used for notification when the state of a toggle reference changes. See g_object_add_toggle_ref().

g_object_add_toggle_ref ()

void                g_object_add_toggle_ref             (GObject *object,
                                                         GToggleNotify notify,
                                                         gpointer data);

Increases the reference count of the object by one and sets a callback to be called when all other references to the object are dropped, or when this is already the last reference to the object and another reference is established.

This functionality is intended for binding object to a proxy object managed by another memory manager. This is done with two paired references: the strong reference added by g_object_add_toggle_ref() and a reverse reference to the proxy object which is either a strong reference or weak reference.

The setup is that when there are no other references to object, only a weak reference is held in the reverse direction from object to the proxy object, but when there are other references held to object, a strong reference is held. The notify callback is called when the reference from object to the proxy object should be toggled from strong to weak (is_last_ref true) or weak to strong (is_last_ref false).

Since a (normal) reference must be held to the object before calling g_object_toggle_ref(), the initial state of the reverse link is always strong.

Multiple toggle references may be added to the same gobject, however if there are multiple toggle references to an object, none of them will ever be notified until all but one are removed. For this reason, you should only ever use a toggle reference if there is important state in the proxy object.

Since 2.8

g_object_remove_toggle_ref ()

void                g_object_remove_toggle_ref          (GObject *object,
                                                         GToggleNotify notify,
                                                         gpointer data);

Removes a reference added with g_object_add_toggle_ref(). The reference count of the object is decreased by one.

Since 2.8

g_object_connect ()

gpointer            g_object_connect                    (gpointer object,
                                                         const gchar *signal_spec,
                                                         ...);

A convenience function to connect multiple signals at once.

The signal specs expected by this function have the form "modifier::signal_name", where modifier can be one of the following:

  menu->toplevel = g_object_connect (g_object_new (GTK_TYPE_WINDOW,
						   "type", GTK_WINDOW_POPUP,
						   "child", menu,
						   NULL),
				     "signal::event", gtk_menu_window_event, menu,
				     "signal::size_request", gtk_menu_window_size_request, menu,
				     "signal::destroy", gtk_widget_destroyed, &menu->toplevel,
				     NULL);

g_object_disconnect ()

void                g_object_disconnect                 (gpointer object,
                                                         const gchar *signal_spec,
                                                         ...);

A convenience function to disconnect multiple signals at once.

The signal specs expected by this function have the form "any_signal", which means to disconnect any signal with matching callback and data, or "any_signal::signal_name", which only disconnects the signal named "signal_name".

g_object_set ()

void                g_object_set                        (gpointer object,
                                                         const gchar *first_property_name,
                                                         ...);

Sets properties on an object.

g_object_get ()

void                g_object_get                        (gpointer object,
                                                         const gchar *first_property_name,
                                                         ...);

Gets properties of an object.

In general, a copy is made of the property contents and the caller is responsible for freeing the memory in the appropriate manner for the type, for instance by calling g_free() or g_object_unref().

 gint intval;
 gchar *strval;
 GObject *objval; 
 
 g_object_get (my_object,
               "intproperty", &intval,
               "strproperty", &strval,
               "objproperty", &objval,
               NULL);

 /* Do something with intval, strval, objval */
 
 g_free (strval);
 g_object_unref (objval);

g_object_notify ()

void                g_object_notify                     (GObject *object,
                                                         const gchar *property_name);

Emits a "notify" signal for the property property_name on object.

g_object_freeze_notify ()

void                g_object_freeze_notify              (GObject *object);

Stops emission of "notify" signals on object. The signals are queued until g_object_thaw_notify() is called on object.

This is necessary for accessors that modify multiple properties to prevent premature notification while the object is still being modified.

g_object_thaw_notify ()

void                g_object_thaw_notify                (GObject *object);

Reverts the effect of a previous call to g_object_freeze_notify(). This causes all queued "notify" signals on object to be emitted.

g_object_get_data ()

gpointer            g_object_get_data                   (GObject *object,
                                                         const gchar *key);

Gets a named field from the objects table of associations (see g_object_set_data()).

g_object_set_data ()

void                g_object_set_data                   (GObject *object,
                                                         const gchar *key,
                                                         gpointer data);

Each object carries around a table of associations from strings to pointers. This function lets you set an association.

If the object already had an association with that name, the old association will be destroyed.

g_object_set_data_full ()

void                g_object_set_data_full              (GObject *object,
                                                         const gchar *key,
                                                         gpointer data,
                                                         GDestroyNotify destroy);

Like g_object_set_data() except it adds notification for when the association is destroyed, either by setting it to a different value or when the object is destroyed.

Note that the destroy callback is not called if data is NULL.

g_object_steal_data ()

gpointer            g_object_steal_data                 (GObject *object,
                                                         const gchar *key);

Remove a specified datum from the object's data associations, without invoking the association's destroy handler.

g_object_get_qdata ()

gpointer            g_object_get_qdata                  (GObject *object,
                                                         GQuark quark);

This function gets back user data pointers stored via g_object_set_qdata().

g_object_set_qdata ()

void                g_object_set_qdata                  (GObject *object,
                                                         GQuark quark,
                                                         gpointer data);

This sets an opaque, named pointer on an object. The name is specified through a GQuark (retrived e.g. via g_quark_from_static_string()), and the pointer can be gotten back from the object with g_object_get_qdata() until the object is finalized. Setting a previously set user data pointer, overrides (frees) the old pointer set, using NULL as pointer essentially removes the data stored.

g_object_set_qdata_full ()

void                g_object_set_qdata_full             (GObject *object,
                                                         GQuark quark,
                                                         gpointer data,
                                                         GDestroyNotify destroy);

This function works like g_object_set_qdata(), but in addition, a void (*destroy) (gpointer) function may be specified which is called with data as argument when the object is finalized, or the data is being overwritten by a call to g_object_set_qdata() with the same quark.

g_object_steal_qdata ()

gpointer            g_object_steal_qdata                (GObject *object,
                                                         GQuark quark);

This function gets back user data pointers stored via g_object_set_qdata() and removes the data from object without invoking it's destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier, for example:

void
object_add_to_user_list (GObject     *object,
                         const gchar *new_string)
{
  /* the quark, naming the object data */
  GQuark quark_string_list = g_quark_from_static_string ("my-string-list");
  /* retrive the old string list */
  GList *list = g_object_steal_qdata (object, quark_string_list);
  
  /* prepend new string */
  list = g_list_prepend (list, g_strdup (new_string));
  /* this changed 'list', so we need to set it again */
  g_object_set_qdata_full (object, quark_string_list, list, free_string_list);
}
static void
free_string_list (gpointer data)
{
  GList *node, *list = data;
  
  for (node = list; node; node = node->next)
    g_free (node->data);
  g_list_free (list);
}

Using g_object_get_qdata() in the above example, instead of g_object_steal_qdata() would have left the destroy function set, and thus the partial string list would have been freed upon g_object_set_qdata_full().

g_object_set_property ()

void                g_object_set_property               (GObject *object,
                                                         const gchar *property_name,
                                                         const GValue *value);

Sets a property on an object.

g_object_get_property ()

void                g_object_get_property               (GObject *object,
                                                         const gchar *property_name,
                                                         GValue *value);

Gets a property of an object.

In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling g_value_unset().

Note that g_object_get_property() is really intended for language bindings, g_object_get() is much more convenient for C programming.

g_object_new_valist ()

GObject*            g_object_new_valist                 (GType object_type,
                                                         const gchar *first_property_name,
                                                         va_list var_args);

Creates a new instance of a GObject subtype and sets its properties.

Construction parameters (see G_PARAM_CONSTRUCT, G_PARAM_CONSTRUCT_ONLY) which are not explicitly specified are set to their default values.

g_object_set_valist ()

void                g_object_set_valist                 (GObject *object,
                                                         const gchar *first_property_name,
                                                         va_list var_args);

Sets properties on an object.

g_object_get_valist ()

void                g_object_get_valist                 (GObject *object,
                                                         const gchar *first_property_name,
                                                         va_list var_args);

Gets properties of an object.

In general, a copy is made of the property contents and the caller is responsible for freeing the memory in the appropriate manner for the type, for instance by calling g_free() or g_object_unref().

See g_object_get().

g_object_watch_closure ()

void                g_object_watch_closure              (GObject *object,
                                                         GClosure *closure);

This function essentially limits the life time of the closure to the life time of the object. That is, when the object is finalized, the closure is invalidated by calling g_closure_invalidate() on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, g_object_ref() and g_object_unref() are added as marshal guards to the closure, to ensure that an extra reference count is held on object during invocation of the closure. Usually, this function will be called on closures that use this object as closure data.

g_object_run_dispose ()

void                g_object_run_dispose                (GObject *object);

Releases all references to other objects. This can be used to break reference cycles.

G_OBJECT_WARN_INVALID_PROPERTY_ID()

#define             G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec)

This macro should be used to emit a standard warning about unexpected properties in set_property() and get_property() implementations.

The "notify" signal

void                user_function                      (GObject    *gobject,
                                                        GParamSpec *arg1,
                                                        gpointer    user_data)      : Run First / No Recursion / Has Details / Action / No Hooks

The notify signal is emitted on an object when one of its properties has been changed. Note that getting this signal doesn't guarantee that the value of the property has actually changed, it may also be emitted when the setter for the property is called to reinstate the previous value.

This signal is typically used to obtain change notification for a single property, by specifying the property name as a detail in the g_signal_connect() call, like this:

g_signal_connect (text_view->buffer, "notify::paste-target-list",
                  G_CALLBACK (gtk_text_view_target_list_notify),
                  text_view)

It is important to note that you must use canonical parameter names as detail strings for the notify signal.