1 <!-- ##### SECTION Title ##### -->
4 <!-- ##### SECTION Short_Description ##### -->
5 Metadata for parameter specifications
7 <!-- ##### SECTION Long_Description ##### -->
9 #GParamSpec is an object structure that encapsulates the metadata
10 required to specify parameters, such as e.g. #GObject properties.
12 <para id="canonical-parameter-name">
13 Parameter names need to start with a letter (a-z or A-Z). Subsequent
14 characters can be letters, numbers or a '-'.
15 All other characters are replaced by a '-' during construction.
16 The result of this replacement is called the canonical name of the
20 <!-- ##### SECTION See_Also ##### -->
22 g_object_class_install_property(), g_object_set(), g_object_get(),
23 g_object_set_property(), g_object_get_property(), g_value_register_transform_func()
26 <!-- ##### SECTION Stability_Level ##### -->
29 <!-- ##### MACRO G_TYPE_IS_PARAM ##### -->
31 Returns whether @type "is a" %G_TYPE_PARAM.
37 <!-- ##### MACRO G_PARAM_SPEC ##### -->
39 Casts a derived #GParamSpec object (e.g. of type #GParamSpecInt) into
43 @pspec: a valid #GParamSpec
46 <!-- ##### MACRO G_IS_PARAM_SPEC ##### -->
48 Checks whether @pspec "is a" valid #GParamSpec structure of type %G_TYPE_PARAM
55 <!-- ##### MACRO G_PARAM_SPEC_CLASS ##### -->
57 Casts a derived #GParamSpecClass structure into a #GParamSpecClass structure.
60 @pclass: a valid #GParamSpecClass
63 <!-- ##### MACRO G_IS_PARAM_SPEC_CLASS ##### -->
65 Checks whether @pclass "is a" valid #GParamSpecClass structure of type
66 %G_TYPE_PARAM or derived.
69 @pclass: a #GParamSpecClass
72 <!-- ##### MACRO G_PARAM_SPEC_GET_CLASS ##### -->
74 Retrieves the #GParamSpecClass of a #GParamSpec.
77 @pspec: a valid #GParamSpec
80 <!-- ##### MACRO G_PARAM_SPEC_TYPE ##### -->
82 Retrieves the #GType of this @pspec.
85 @pspec: a valid #GParamSpec
88 <!-- ##### MACRO G_PARAM_SPEC_TYPE_NAME ##### -->
90 Retrieves the #GType name of this @pspec.
93 @pspec: a valid #GParamSpec
96 <!-- ##### MACRO G_PARAM_SPEC_VALUE_TYPE ##### -->
98 Retrieves the #GType to initialize a #GValue for this parameter.
101 @pspec: a valid #GParamSpec
104 <!-- ##### STRUCT GParamSpec ##### -->
106 All fields of the <structname>GParamSpec</structname> struct are private and
107 should not be used directly, except for the following:
110 @g_type_instance: private #GTypeInstance portion
111 @name: name of this parameter
112 @flags: #GParamFlags flags for this parameter
113 @value_type: the #GValue type for this parameter
114 @owner_type: #GType type that uses (introduces) this paremeter
116 <!-- ##### STRUCT GParamSpecClass ##### -->
118 The class structure for the <structname>GParamSpec</structname> type.
119 Normally, <structname>GParamSpec</structname> classes are filled by
120 g_param_type_register_static().
123 @g_type_class: the parent class
124 @value_type: the #GValue type for this parameter
125 @finalize: The instance finalization function (optional), should chain
126 up to the finalize method of the parent class.
127 @value_set_default: Resets a @value to the default value for this type
128 (recommended, the default is g_value_reset()), see
129 g_param_value_set_default().
130 @value_validate: Ensures that the contents of @value comply with the
131 specifications set out by this type (optional), see
132 g_param_value_set_validate().
133 @values_cmp: Compares @value1 with @value2 according to this type
134 (recommended, the default is memcmp()), see g_param_values_cmp().
136 <!-- ##### ENUM GParamFlags ##### -->
138 Through the #GParamFlags flag values, certain aspects of parameters
142 @G_PARAM_READABLE: the parameter is readable
143 @G_PARAM_WRITABLE: the parameter is writable
144 @G_PARAM_CONSTRUCT: the parameter will be set upon object construction
145 @G_PARAM_CONSTRUCT_ONLY: the parameter will only be set upon object construction
146 @G_PARAM_LAX_VALIDATION: upon parameter conversion (see g_param_value_convert())
147 strict validation is not required
148 @G_PARAM_STATIC_NAME: the string used as name when constructing the
149 parameter is guaranteed to remain valid and
150 unmodified for the lifetime of the parameter.
153 @G_PARAM_STATIC_NICK:
154 @G_PARAM_STATIC_BLURB: the string used as blurb when constructing the
155 parameter is guaranteed to remain valid and
156 unmodified for the lifetime of the parameter.
159 <!-- ##### MACRO G_PARAM_READWRITE ##### -->
161 #GParamFlags value alias for %G_PARAM_READABLE | %G_PARAM_WRITABLE.
166 <!-- ##### MACRO G_PARAM_STATIC_STRINGS ##### -->
168 #GParamFlags value alias for %G_PARAM_STATIC_NAME | %G_PARAM_STATIC_NICK | %G_PARAM_STATIC_BLURB.
173 <!-- ##### MACRO G_PARAM_MASK ##### -->
175 Mask containing the bits of #GParamSpec.flags which are reserved for GLib.
180 <!-- ##### MACRO G_PARAM_USER_SHIFT ##### -->
182 Minimum shift count to be used for user defined flags, to be stored in
188 <!-- ##### FUNCTION g_param_spec_ref ##### -->
190 Increments the reference count of @pspec.
193 @pspec: a valid #GParamSpec
194 @Returns: the #GParamSpec that was passed into this function
197 <!-- ##### FUNCTION g_param_spec_unref ##### -->
199 Decrements the reference count of a @pspec.
202 @pspec: a valid #GParamSpec
205 <!-- ##### FUNCTION g_param_spec_sink ##### -->
207 The initial reference count of a newly created #GParamSpec is 1, even
208 though no one has explicitly called g_param_spec_ref() on it yet. So the
209 initial reference count is flagged as "floating", until someone calls
210 <literal>g_param_spec_ref (pspec); g_param_spec_sink (pspec);</literal>
211 in sequence on it, taking over the initial reference count (thus
212 ending up with a @pspec that has a reference count of 1 still, but is
213 not flagged "floating" anymore).
216 @pspec: a valid #GParamSpec
219 <!-- ##### FUNCTION g_param_spec_ref_sink ##### -->
221 Convenience function to ref and sink a #GParamSpec.
224 @pspec: a valid #GParamSpec
225 @Returns: the #GParamSpec that was passed into this function
229 <!-- ##### FUNCTION g_param_value_set_default ##### -->
231 Sets @value to its default value as specified in @pspec.
234 @pspec: a valid #GParamSpec
235 @value: a #GValue of correct type for @pspec
238 <!-- ##### FUNCTION g_param_value_defaults ##### -->
240 Checks whether @value contains the default value as specified in @pspec.
243 @pspec: a valid #GParamSpec
244 @value: a #GValue of correct type for @pspec
245 @Returns: whether @value contains the canonical default for this @pspec
248 <!-- ##### FUNCTION g_param_value_validate ##### -->
250 Ensures that the contents of @value comply with the specifications
251 set out by @pspec. For example, a #GParamSpecInt might require
252 that integers stored in @value may not be smaller than -42 and not be
253 greater than +42. If @value contains an integer outside of this range,
254 it is modified accordingly, so the resulting value will fit into the
258 @pspec: a valid #GParamSpec
259 @value: a #GValue of correct type for @pspec
260 @Returns: whether modifying @value was necessary to ensure validity
263 <!-- ##### FUNCTION g_param_value_convert ##### -->
265 Transforms @src_value into @dest_value if possible, and then validates
266 @dest_value, in order for it to conform to @pspec.
267 If @strict_validation is %TRUE this function will only succeed if
268 the transformed @dest_value complied to @pspec without modifications.
270 See also g_value_type_transformable(), g_value_transform() and
271 g_param_value_validate().
274 @pspec: a valid #GParamSpec
275 @src_value: souce #GValue
276 @dest_value: destination #GValue of correct type for @pspec
277 @strict_validation: %TRUE requires @dest_value to conform to @pspec without modifications
278 @Returns: %TRUE if transformation and validation were successful,
279 %FALSE otherwise and @dest_value is left untouched.
282 <!-- ##### FUNCTION g_param_values_cmp ##### -->
284 Compares @value1 with @value2 according to @pspec, and return -1, 0 or +1,
285 if @value1 is found to be less than, equal to or greater than @value2,
289 @pspec: a valid #GParamSpec
290 @value1: a #GValue of correct type for @pspec
291 @value2: a #GValue of correct type for @pspec
292 @Returns: -1, 0 or +1, for a less than, equal to or greater than result
295 <!-- ##### FUNCTION g_param_spec_get_name ##### -->
297 Returns the name of a #GParamSpec.
300 @pspec: a valid #GParamSpec
301 @Returns: the name of @pspec.
304 <!-- ##### FUNCTION g_param_spec_get_nick ##### -->
306 Returns the nickname of a #GParamSpec.
309 @pspec: a valid #GParamSpec
310 @Returns: the nickname of @pspec.
313 <!-- ##### FUNCTION g_param_spec_get_blurb ##### -->
315 Returns the short description of a #GParamSpec.
318 @pspec: a valid #GParamSpec
319 @Returns: the short description of @pspec.
322 <!-- ##### FUNCTION g_param_spec_get_qdata ##### -->
324 Gets back user data pointers stored via g_param_spec_set_qdata().
327 @pspec: a valid #GParamSpec
328 @quark: a #GQuark, naming the user data pointer
329 @Returns: the user data pointer set, or %NULL
332 <!-- ##### FUNCTION g_param_spec_set_qdata ##### -->
334 Sets an opaque, named pointer on a #GParamSpec. The name is specified
335 through a #GQuark (retrieved e.g. via g_quark_from_static_string()), and
336 the pointer can be gotten back from the @pspec with g_param_spec_get_qdata().
337 Setting a previously set user data pointer, overrides (frees)
338 the old pointer set, using %NULL as pointer essentially
339 removes the data stored.
342 @pspec: the #GParamSpec to set store a user data pointer
343 @quark: a #GQuark, naming the user data pointer
344 @data: an opaque user data pointer
347 <!-- ##### FUNCTION g_param_spec_set_qdata_full ##### -->
349 This function works like g_param_spec_set_qdata(), but in addition,
350 a <literal>void (*destroy) (gpointer)</literal> function may be
351 specified which is called with @data as argument when the @pspec is
352 finalized, or the data is being overwritten by a call to
353 g_param_spec_set_qdata() with the same @quark.
356 @pspec: the #GParamSpec to set store a user data pointer
357 @quark: a #GQuark, naming the user data pointer
358 @data: an opaque user data pointer
359 @destroy: function to invoke with @data as argument, when @data needs to
363 <!-- ##### FUNCTION g_param_spec_steal_qdata ##### -->
365 Gets back user data pointers stored via g_param_spec_set_qdata() and
366 removes the @data from @pspec without invoking it's destroy() function
368 Usually, calling this function is only required to update
369 user data pointers with a destroy notifier.
372 @pspec: the #GParamSpec to get a stored user data pointer from
373 @quark: a #GQuark, naming the user data pointer
374 @Returns: the user data pointer set, or %NULL
377 <!-- ##### FUNCTION g_param_spec_get_redirect_target ##### -->
379 If the paramspec redirects operations to another paramspec,
380 returns that paramspec. Redirect is used typically for
381 providing a new implementation of a property in a derived
382 type while preserving all the properties from the parent
383 type. Redirection is established by creating a property
384 of type #GParamSpecOverride. See g_object_override_property()
385 for an example of the use of this capability.
388 @pspec: a #GParamSpec
389 @Returns: paramspec to which requests on this paramspec should
390 be redirected, or %NULL if none.
394 <!-- ##### FUNCTION g_param_spec_internal ##### -->
396 Creates a new #GParamSpec instance.
399 A property name consists of segments consisting of ASCII letters and
400 digits, separated by either the '-' or '_' character. The first
401 character of a property name must be a letter. Names which violate these
402 rules lead to undefined behaviour.
405 When creating and looking up a #GParamSpec, either separator can be used,
406 but they cannot be mixed. Using '-' is considerably more efficient and in
407 fact required when using property names as detail strings for signals.
410 @param_type: the #GType for the property; must be derived from #G_TYPE_PARAM
411 @name: the canonical name of the property
412 @nick: the nickname of the property
413 @blurb: a short description of the property
414 @flags: a combination of #GParamFlags
415 @Returns: a newly allocated #GParamSpec instance
418 <!-- ##### STRUCT GParamSpecTypeInfo ##### -->
420 This structure is used to provide the type system with the information
421 required to initialize and destruct (finalize) a parameter's class and
423 The initialized structure is passed to the g_param_type_register_static()
424 The type system will perform a deep copy of this structure, so it's memory
425 does not need to be persistent across invocation of
426 g_param_type_register_static().
429 @instance_size: Size of the instance (object) structure.
430 @n_preallocs: Prior to GLib 2.10, it specified the number of pre-allocated (cached) instances to reserve memory for (0 indicates no caching). Since GLib 2.10, it is ignored, since instances are allocated with the <link linkend="glib-Memory-Slices">slice allocator</link> now.
431 @instance_init: Location of the instance initialization function (optional).
432 @value_type: The #GType of values conforming to this #GParamSpec
433 @finalize: The instance finalization function (optional).
434 @value_set_default: Resets a @value to the default value for @pspec
435 (recommended, the default is g_value_reset()), see
436 g_param_value_set_default().
437 @value_validate: Ensures that the contents of @value comply with the
438 specifications set out by @pspec (optional), see
439 g_param_value_set_validate().
440 @values_cmp: Compares @value1 with @value2 according to @pspec
441 (recommended, the default is memcmp()), see g_param_values_cmp().
443 <!-- ##### FUNCTION g_param_type_register_static ##### -->
445 Registers @name as the name of a new static type derived from
446 #G_TYPE_PARAM. The type system uses the information contained in the
447 #GParamSpecTypeInfo structure pointed to by @info to manage the #GParamSpec
448 type and its instances.
451 @name: 0-terminated string used as the name of the new #GParamSpec type.
452 @pspec_info: The #GParamSpecTypeInfo for this #GParamSpec type.
453 @Returns: The new type identifier.
456 <!-- ##### STRUCT GParamSpecPool ##### -->
458 A #GParamSpecPool maintains a collection of #GParamSpec<!-- -->s which can be
459 quickly accessed by owner and name. The implementation of the #GObject property
460 system uses such a pool to store the #GParamSpecs of the properties all object
465 <!-- ##### FUNCTION g_param_spec_pool_new ##### -->
467 Creates a new #GParamSpecPool.
470 If @type_prefixing is %TRUE, lookups in the newly created pool will
471 allow to specify the owner as a colon-separated prefix of the property name,
472 like "GtkContainer:border-width". This feature is deprecated, so you should
473 always set @type_prefixing to %FALSE.
476 @type_prefixing: Whether the pool will support type-prefixed property names.
477 @Returns: a newly allocated #GParamSpecPool.
480 <!-- ##### FUNCTION g_param_spec_pool_insert ##### -->
482 Inserts a #GParamSpec in the pool.
485 @pool: a #GParamSpecPool.
486 @pspec: the #GParamSpec to insert
487 @owner_type: a #GType identifying the owner of @pspec
490 <!-- ##### FUNCTION g_param_spec_pool_remove ##### -->
492 Removes a #GParamSpec from the pool.
495 @pool: a #GParamSpecPool
496 @pspec: the #GParamSpec to remove
499 <!-- ##### FUNCTION g_param_spec_pool_lookup ##### -->
501 Looks up a #GParamSpec in the pool.
504 @pool: a #GParamSpecPool
505 @param_name: the name to look for
506 @owner_type: the owner to look for
507 @walk_ancestors: If %TRUE, also try to find a #GParamSpec with @param_name
508 owned by an ancestor of @owner_type.
509 @Returns: The found #GParamSpec, or %NULL if no matching #GParamSpec was found.
512 <!-- ##### FUNCTION g_param_spec_pool_list ##### -->
514 Gets an array of all #GParamSpec<!-- -->s owned by @owner_type in the pool.
517 @pool: a #GParamSpecPool
518 @owner_type: the owner to look for
519 @n_pspecs_p: return location for the length of the returned array
520 @Returns: a newly allocated array containing pointers to all
521 #GParamSpec<!-- -->s owned by @owner_type in the pool
524 <!-- ##### FUNCTION g_param_spec_pool_list_owned ##### -->
526 Gets an #GList of all #GParamSpec<!-- -->s owned by @owner_type in the pool.
529 @pool: a #GParamSpecPool
530 @owner_type: the owner to look for
531 @Returns: a #GList of all #GParamSpec<!-- -->s owned by @owner_type in
532 the pool#GParamSpec<!-- -->s.