GObject The base object type GObject is the fundamental type providing the common attributes and methods for all object types in GTK+, Pango and other libraries based on GObject. The GObject class provides methods for object construction and destruction, property access methods, and signal support. Signals are described in detail in . #GInitiallyUnowned is derived from #GObject. The only difference between the two is that the initial reference of a #GInitiallyUnowned is flagged as a floating reference. This means that it is not specifically claimed to be "owned" by any code portion. The main motivation for providing floating references is C convenience. In particular, it allows code to be written as: container = create_container(); container_add_child (container, create_child()); If container_add_child() will g_object_ref_sink() the passed in child, no reference of the newly created child is leaked. Without floating references, container_add_child() can only g_object_ref() the new child, so to implement this code without reference leaks, it would have to be written as: Child *child; container = create_container(); child = create_child(); container_add_child (container, child); g_object_unref (child); The floating reference can be converted into an ordinary reference by calling g_object_ref_sink(). For already sunken objects (objects that don't have a floating reference anymore), g_object_ref_sink() is equivalent to g_object_ref() and returns a new reference. Since floating references are useful almost exclusively for C convenience, language bindings that provide automated reference and memory ownership maintenance (such as smart pointers or garbage collection) therefore don't need to expose floating references in their API. Some object implementations may need to save an objects floating state across certain code portions (an example is #GtkMenu), to achive this, the following sequence can be used: /* save floating state */ gboolean was_floating = g_object_is_floating (object); g_object_ref_sink (object); /* protected code portion */ ...; /* restore floating state */ if (was_floating) g_object_force_floating (object); g_obejct_unref (object); /* release previously acquired reference */ #GParamSpecObject, g_param_spec_object() All the fields in the GObject structure are private to the #GObject implementation and should never be accessed directly. 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. @pspec: the #GParamSpec of the property which changed @gobject: the object which received the signal. 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; } @g_type_class: the parent class @constructor: the @constructor function is called by g_object_new () to complete the object initialization after all the construction properties are set. The first thing a @constructor implementation must do is chain up to the @constructor of the parent class. Overriding @constructor should be rarely needed, e.g. to handle construct properties, or to implement singletons. @set_property: the generic setter for all properties of this type. Should be overridden for every type with properties. Implementations of @set_property don't need to emit property change notification explicitly, this is handled by the type system. @get_property: the generic getter for all properties of this type. Should be overridden for every type with properties. @dispose: the @dispose function is supposed to drop all references to other objects, but keep the instance otherwise intact, so that client method invocations still work. It may be run multiple times (due to reference loops). Before returning, @dispose should chain up to the @dispose method of the parent class. @finalize: instance finalization function, should finish the finalization of the instance begun in @dispose and chain up to the @finalize method of the parent class. @dispatch_properties_changed: emits property change notification for a bunch of properties. Overriding @dispatch_properties_changed should be rarely needed. @notify: the class closure for the notify signal The GObjectConstructParam struct is an auxiliary structure used to hand #GParamSpec/#GValue pairs to the @constructor of a #GObjectClass. @pspec: the #GParamSpec of the construct parameter @value: the value to set the parameter to The type of the @get_property function of #GObjectClass. @object: a #GObject @property_id: the numeric id under which the property was registered with g_object_class_install_property(). @value: a #GValue to return the property value in @pspec: the #GParamSpec describing the property The type of the @set_property function of #GObjectClass. @object: a #GObject @property_id: the numeric id under which the property was registered with g_object_class_install_property(). @value: the new value for the property @pspec: the #GParamSpec describing the property The type of the @finalize function of #GObjectClass. @object: the #GObject being finalized Returns a boolean value of %FALSE or %TRUE indicating whether the passed in type id is a %G_TYPE_OBJECT or derived from it. @type: Type id to check for is a %G_TYPE_OBJECT relationship. @Returns: %FALSE or %TRUE, indicating whether @type is a %G_TYPE_OBJECT. 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. @object: Object which is subject to casting. Checks whether a valid #GTypeInstance pointer is of type %G_TYPE_OBJECT. @object: Instance to check for being a %G_TYPE_OBJECT. Casts a derived #GObjectClass structure into a #GObjectClass structure. @class: a valid #GObjectClass Checks whether @class "is a" valid #GObjectClass structure of type %G_TYPE_OBJECT or derived. @class: a #GObjectClass Returns the class structure associated to a #GObject instance. @object: a #GObject instance. Return the type id of an object. @object: Object to return the type id for. @Returns: Type id of @object. Returns the name of an object's type. @object: Object to return the type name for. @Returns: Type name of @object. The string is owned by the type system and should not be freed. Return the type id of a class structure. @class: a valid #GObjectClass @Returns: Type id of @class. Return the name of a class structure's type. @class: a valid #GObjectClass @Returns: Type name of @class. The string is owned by the type system and should not be freed. Installs a new property. This is usually done in the class initializer. @oclass: a #GObjectClass @property_id: the id for the new property @pspec: the #GParamSpec for the new property Looks up the #GParamSpec for a property of a class. @oclass: a #GObjectClass @property_name: the name of the property to look up @Returns: the #GParamSpec for the property, or %NULL if the class doesn't have a property of that name Returns an array of #GParamSpec* for all properties of a class. @oclass: a #GObjectClass @n_properties: return location for the length of the returned array @Returns: an array of #GParamSpec* which should be freed after use 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. Internally, overriding is implemented by creating a property of type #GParamSpecOverride; generally operations that query the properties of the object class, such as g_object_class_find_property() or g_object_class_list_properties() will return the overridden property. However, in one case, the @construct_properties argument of the @constructor virtual function, the #GParamSpecOverride is passed instead, so that the @param_id field of the #GParamSpec will be correct. For virtually all uses, this makes no difference. If you need to get the overridden property, you can call g_param_spec_get_redirect_target(). @oclass: a #GObjectClass @property_id: the new property ID @name: the name of a property registered in a parent class or in an interface of this class. @Since: 2.4 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. @g_iface: any interface vtable for the interface, or the default vtable for the interface. @pspec: the #GParamSpec for the new property @Since: 2.4 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(). @g_iface: any interface vtable for the interface, or the default vtable for the interface @property_name: name of a property to lookup. @Returns: the #GParamSpec for the property of the interface with the name @property_name, or %NULL if no such property exists. @Since: 2.4 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(). @g_iface: any interface vtable for the interface, or the default vtable for the interface @n_properties_p: location to store number of properties returned. @Returns: a pointer to an array of pointers to #GParamSpec structures. The paramspecs are owned by GLib, but the array should be freed with g_free() when you are done with it. @Since: 2.4 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. @object_type: the type id of the #GObject subtype to instantiate @first_property_name: the name of the first property @Varargs: the value of the first property, followed optionally by more name/value pairs, followed by %NULL @Returns: a new instance of @object_type 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. @object_type: the type id of the #GObject subtype to instantiate @n_parameters: the length of the @parameters array @parameters: an array of #GParameter @Returns: a new instance of @object_type The GParameter struct is an auxiliary structure used to hand parameter name/value pairs to g_object_newv(). @name: the parameter name @value: the parameter value Increases the reference count of @object. @object: a #GObject @Returns: the same @object Decreases the reference count of @object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed). @object: a #GObject 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. @object: a #GObject @Returns: @object @Since: 2.10 All the fields in the GInitiallyUnowned structure are private to the #GInitiallyUnowned implementation and should never be accessed directly. The class structure for the GInitiallyUnowned type. The type for #GInitiallyUnowned. Checks wether @object has a floating reference. @object: a #GObject @Returns: %TRUE if @object has a floating reference @Since: 2.10 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(). @object: a #GObject @Since: 2.10 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. @data: data that was provided when the weak reference was established @where_the_object_was: the object being finalized 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). @object: #GObject to reference weakly @notify: callback to invoke before the object is freed @data: extra data to pass to notify Removes a weak reference callback to an object. @object: #GObject to remove a weak reference from @notify: callback to search for @data: data to search for 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. @object: The object that should be weak referenced. @weak_pointer_location: The memory address of a pointer. 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(). @object: The object that is weak referenced. @weak_pointer_location: The memory address of a pointer. A callback function used for notification when the state of a toggle reference changes. See g_object_add_toggle_ref(). @data: Callback data passed to g_object_add_toggle_ref() @object: The object on which g_object_add_toggle_ref() was called. @is_last_ref: %TRUE if the toggle reference is now the last reference to the object. %FALSE if the toggle reference was the last reference and there are now other references. 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. @object: a #GObject @notify: a function to call when this reference is the last reference to the object, or is no longer the last reference. @data: data to pass to @notify @Since: 2.8 Removes a reference added with g_object_add_toggle_ref(). The reference count of the object is decreased by one. @object: a #GObject @notify: a function to call when this reference is the last reference to the object, or is no longer the last reference. @data: data to pass to @notify @Since: 2.8 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: signal equivalent to g_signal_connect_data (...) object_signal object-signal equivalent to g_signal_connect_object (...) swapped_signal swapped-signal equivalent to g_signal_connect_data (..., G_CONNECT_SWAPPED) swapped_object_signal swapped-object-signal equivalent to g_signal_connect_object (..., G_CONNECT_SWAPPED) signal_after signal-after equivalent to g_signal_connect_data (..., G_CONNECT_AFTER) object_signal_after object-signal-after equivalent to g_signal_connect_object (..., G_CONNECT_AFTER) swapped_signal_after swapped-signal-after equivalent to g_signal_connect_data (..., G_CONNECT_SWAPPED | G_CONNECT_AFTER) swapped_object_signal_after swapped-object-signal-after equivalent to g_signal_connect_object (..., G_CONNECT_SWAPPED | G_CONNECT_AFTER) 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); @object: a #GObject @signal_spec: the spec for the first signal @Varargs: #GCallback for the first signal, followed by data for the first signal, followed optionally by more signal spec/callback/data triples, followed by %NULL @Returns: @object 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". @object: a #GObject @signal_spec: the spec for the first signal @Varargs: #GCallback for the first signal, followed by data for the first signal, followed optionally by more signal spec/callback/data triples, followed by %NULL Sets properties on an object. @object: a #GObject @first_property_name: name of the first property to set @Varargs: value for the first property, followed optionally by more name/value pairs, followed by %NULL 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(). An example of using g_object_get() to get the contents of three properties - one of type #G_TYPE_INT, one of type #G_TYPE_STRING, and one of type #G_TYPE_OBJECT: 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); @object: a #GObject @first_property_name: name of the first property to get @Varargs: return location for the first property, followed optionally by more name/return location pairs, followed by %NULL Emits a "notify" signal for the property @property_name on @object. @object: a #GObject @property_name: the name of a property installed on the class of @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. @object: a #GObject Reverts the effect of a previous call to g_object_freeze_notify(). This causes all queued "notify" signals on @object to be emitted. @object: a #GObject Gets a named field from the objects table of associations (see g_object_set_data()). @object: #GObject containing the associations @key: name of the key for that association @Returns: the data if found, or %NULL if no such data exists. 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. @object: #GObject containing the associations. @key: name of the key @data: data to associate with that key 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. @object: #GObject containing the associations @key: name of the key @data: data to associate with that key @destroy: function to call when the association is destroyed Remove a specified datum from the object's data associations, without invoking the association's destroy handler. @object: #GObject containing the associations @key: name of the key @Returns: the data if found, or %NULL if no such data exists. This function gets back user data pointers stored via g_object_set_qdata(). @object: The GObject to get a stored user data pointer from @quark: A #GQuark, naming the user data pointer @Returns: The user data pointer set, or %NULL 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. @object: The GObject to set store a user data pointer @quark: A #GQuark, naming the user data pointer @data: An opaque user data pointer 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. @object: The GObject to set store a user data pointer @quark: A #GQuark, naming the user data pointer @data: An opaque user data pointer @destroy: Function to invoke with @data as argument, when @data needs to be freed 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(). @object: The GObject to get a stored user data pointer from @quark: A #GQuark, naming the user data pointer @Returns: The user data pointer set, or %NULL Sets a property on an object. @object: a #GObject @property_name: the name of the property to set @value: the 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. @object: a #GObject @property_name: the name of the property to get @value: return location for the property value 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. @object_type: the type id of the #GObject subtype to instantiate @first_property_name: the name of the first property @var_args: the value of the first property, followed optionally by more name/value pairs, followed by %NULL @Returns: a new instance of @object_type Sets properties on an object. @object: a #GObject @first_property_name: name of the first property to set @var_args: value for the first property, followed optionally by more name/value pairs, followed by %NULL 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(). @object: a #GObject @first_property_name: name of the first property to get @var_args: return location for the first property, followed optionally by more name/return location pairs, followed by %NULL 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. @object: GObject restricting lifetime of @closure @closure: GClosure to watch Releases all references to other objects. This can be used to break reference cycles. This functions should only be called from object system implementations. @object: a #GObject This macros should be used to emit a standard warning about unexpected properties in set_property() and get_property() implementations. @object: the #GObject on which set_property() or get_property() was called @property_id: the numeric id of the property @pspec: the #GParamSpec of the property