gio/gactiongroup.c

   1 /*
   2  * Copyright © 2010 Codethink Limited
   3  *
   4  * This program is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License as published
   6  * by the Free Software Foundation; either version 2 of the licence or (at
   7  * your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General
  15  * Public License along with this library; if not, write to the
  16  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  17  * Boston, MA 02111-1307, USA.
  18  *
  19  * Authors: Ryan Lortie <desrt@desrt.ca>
  20  */
  21
  22 #include "config.h"
  23 #include "gactiongroup.h"
  24 #include "gaction.h"
  25 #include "glibintl.h"
  26
  27 /**
  28  * SECTION:gactiongroup
  29  * @title: GActionGroup
  30  * @short_description: A group of actions
  31  *
  32  * #GActionGroup represents a group of actions.
  33  *
  34  * Each action in the group has a unique name (which is a string).  All
  35  * method calls, except g_action_group_list_actions() take the name of
  36  * an action as an argument.
  37  *
  38  * Action groups are often used together with a #GMenuModel that provides
  39  * additional representation data for the actions.
  40  *
  41  * The #GActionGroup API is meant to be the 'public' API to the action
  42  * group.  The calls here are exactly the interaction that 'external
  43  * forces' (eg: UI, incoming D-Bus messages, etc.) are supposed to have
  44  * with actions.  'Internal' APIs (ie: ones meant only to be accessed by
  45  * the action group implementation) are found on subclasses.  This is
  46  * why you will find - for example - g_action_group_get_action_enabled()
  47  * but not an equivalent <function>set()</function> call.
  48  *
  49  * Signals are emitted on the action group in response to state changes
  50  * on individual actions.
  51  *
  52  * Implementations of #GActionGroup should provide implementations for
  53  * the virtual functions g_action_group_list_actions() and
  54  * g_action_group_query_action().  The other virtual functions should
  55  * not be implemented - their "wrappers" are actually implemented with
  56  * calls to g_action_group_query_action().
  57  **/
  58
  59 G_DEFINE_INTERFACE (GActionGroup, g_action_group, G_TYPE_OBJECT)
  60
  61 enum
  62 {
  63   SIGNAL_ACTION_ADDED,
  64   SIGNAL_ACTION_REMOVED,
  65   SIGNAL_ACTION_ENABLED_CHANGED,
  66   SIGNAL_ACTION_STATE_CHANGED,
  67   NR_SIGNALS
  68 };
  69
  70 static guint g_action_group_signals[NR_SIGNALS];
  71
  72 static gboolean
  73 g_action_group_real_has_action (GActionGroup *action_group,
  74                                 const gchar  *action_name)
  75 {
  76   return g_action_group_query_action (action_group, action_name, NULL, NULL, NULL, NULL, NULL);
  77 }
  78
  79 static gboolean
  80 g_action_group_real_get_action_enabled (GActionGroup *action_group,
  81                                         const gchar  *action_name)
  82 {
  83   gboolean enabled = FALSE;
  84
  85   g_action_group_query_action (action_group, action_name, &enabled, NULL, NULL, NULL, NULL);
  86
  87   return enabled;
  88 }
  89
  90 static const GVariantType *
  91 g_action_group_real_get_action_parameter_type (GActionGroup *action_group,
  92                                                const gchar  *action_name)
  93 {
  94   const GVariantType *type = NULL;
  95
  96   g_action_group_query_action (action_group, action_name, NULL, &type, NULL, NULL, NULL);
  97
  98   return type;
  99 }
 100
 101 static const GVariantType *
 102 g_action_group_real_get_action_state_type (GActionGroup *action_group,
 103                                            const gchar  *action_name)
 104 {
 105   const GVariantType *type = NULL;
 106
 107   g_action_group_query_action (action_group, action_name, NULL, NULL, &type, NULL, NULL);
 108
 109   return type;
 110 }
 111
 112 static GVariant *
 113 g_action_group_real_get_action_state_hint (GActionGroup *action_group,
 114                                            const gchar  *action_name)
 115 {
 116   GVariant *hint = NULL;
 117
 118   g_action_group_query_action (action_group, action_name, NULL, NULL, NULL, &hint, NULL);
 119
 120   return hint;
 121 }
 122
 123 static GVariant *
 124 g_action_group_real_get_action_state (GActionGroup *action_group,
 125                                       const gchar  *action_name)
 126 {
 127   GVariant *state = NULL;
 128
 129   g_action_group_query_action (action_group, action_name, NULL, NULL, NULL, NULL, &state);
 130
 131   return state;
 132 }
 133
 134 static gboolean
 135 g_action_group_real_query_action (GActionGroup        *action_group,
 136                                   const gchar         *action_name,
 137                                   gboolean            *enabled,
 138                                   const GVariantType **parameter_type,
 139                                   const GVariantType **state_type,
 140                                   GVariant           **state_hint,
 141                                   GVariant           **state)
 142 {
 143   GActionGroupInterface *iface = G_ACTION_GROUP_GET_IFACE (action_group);
 144
 145   /* we expect implementations to override this method, but we also
 146    * allow for implementations that existed before this method was
 147    * introduced to override the individual accessors instead.
 148    *
 149    * detect the case that neither has happened and report it.
 150    */
 151   if G_UNLIKELY (iface->has_action == g_action_group_real_has_action ||
 152                  iface->get_action_enabled == g_action_group_real_get_action_enabled ||
 153                  iface->get_action_parameter_type == g_action_group_real_get_action_parameter_type ||
 154                  iface->get_action_state_type == g_action_group_real_get_action_state_type ||
 155                  iface->get_action_state_hint == g_action_group_real_get_action_state_hint ||
 156                  iface->get_action_state == g_action_group_real_get_action_state)
 157     {
 158       g_critical ("Class '%s' implements GActionGroup interface without overriding "
 159                   "query_action() method -- bailing out to avoid infinite recursion.",
 160                   G_OBJECT_TYPE_NAME (action_group));
 161       return FALSE;
 162     }
 163
 164   if (!(* iface->has_action) (action_group, action_name))
 165     return FALSE;
 166
 167   if (enabled != NULL)
 168     *enabled = (* iface->get_action_enabled) (action_group, action_name);
 169
 170   if (parameter_type != NULL)
 171     *parameter_type = (* iface->get_action_parameter_type) (action_group, action_name);
 172
 173   if (state_type != NULL)
 174     *state_type = (* iface->get_action_state_type) (action_group, action_name);
 175
 176   if (state_hint != NULL)
 177     *state_hint = (* iface->get_action_state_hint) (action_group, action_name);
 178
 179   if (state != NULL)
 180     *state = (* iface->get_action_state) (action_group, action_name);
 181
 182   return TRUE;
 183 }
 184
 185 static void
 186 g_action_group_default_init (GActionGroupInterface *iface)
 187 {
 188   iface->has_action = g_action_group_real_has_action;
 189   iface->get_action_enabled = g_action_group_real_get_action_enabled;
 190   iface->get_action_parameter_type = g_action_group_real_get_action_parameter_type;
 191   iface->get_action_state_type = g_action_group_real_get_action_state_type;
 192   iface->get_action_state_hint = g_action_group_real_get_action_state_hint;
 193   iface->get_action_state = g_action_group_real_get_action_state;
 194   iface->query_action = g_action_group_real_query_action;
 195
 196   /**
 197    * GActionGroup::action-added:
 198    * @action_group: the #GActionGroup that changed
 199    * @action_name: the name of the action in @action_group
 200    *
 201    * Signals that a new action was just added to the group.
 202    * This signal is emitted after the action has been added
 203    * and is now visible.
 204    *
 205    * Since: 2.28
 206    **/
 207   g_action_group_signals[SIGNAL_ACTION_ADDED] =
 208     g_signal_new (I_("action-added"),
 209                   G_TYPE_ACTION_GROUP,
 210                   G_SIGNAL_RUN_LAST | G_SIGNAL_DETAILED,
 211                   G_STRUCT_OFFSET (GActionGroupInterface, action_added),
 212                   NULL, NULL,
 213                   g_cclosure_marshal_VOID__STRING,
 214                   G_TYPE_NONE, 1,
 215                   G_TYPE_STRING);
 216
 217   /**
 218    * GActionGroup::action-removed:
 219    * @action_group: the #GActionGroup that changed
 220    * @action_name: the name of the action in @action_group
 221    *
 222    * Signals that an action is just about to be removed from the group.
 223    * This signal is emitted before the action is removed, so the action
 224    * is still visible and can be queried from the signal handler.
 225    *
 226    * Since: 2.28
 227    **/
 228   g_action_group_signals[SIGNAL_ACTION_REMOVED] =
 229     g_signal_new (I_("action-removed"),
 230                   G_TYPE_ACTION_GROUP,
 231                   G_SIGNAL_RUN_LAST | G_SIGNAL_DETAILED,
 232                   G_STRUCT_OFFSET (GActionGroupInterface, action_removed),
 233                   NULL, NULL,
 234                   g_cclosure_marshal_VOID__STRING,
 235                   G_TYPE_NONE, 1,
 236                   G_TYPE_STRING);
 237
 238
 239   /**
 240    * GActionGroup::action-enabled-changed:
 241    * @action_group: the #GActionGroup that changed
 242    * @action_name: the name of the action in @action_group
 243    * @enabled: whether the action is enabled or not
 244    *
 245    * Signals that the enabled status of the named action has changed.
 246    *
 247    * Since: 2.28
 248    **/
 249   g_action_group_signals[SIGNAL_ACTION_ENABLED_CHANGED] =
 250     g_signal_new (I_("action-enabled-changed"),
 251                   G_TYPE_ACTION_GROUP,
 252                   G_SIGNAL_RUN_LAST | G_SIGNAL_DETAILED,
 253                   G_STRUCT_OFFSET (GActionGroupInterface,
 254                                    action_enabled_changed),
 255                   NULL, NULL,
 256                   NULL,
 257                   G_TYPE_NONE, 2,
 258                   G_TYPE_STRING,
 259                   G_TYPE_BOOLEAN);
 260
 261   /**
 262    * GActionGroup::action-state-changed:
 263    * @action_group: the #GActionGroup that changed
 264    * @action_name: the name of the action in @action_group
 265    * @value: the new value of the state
 266    *
 267    * Signals that the state of the named action has changed.
 268    *
 269    * Since: 2.28
 270    **/
 271   g_action_group_signals[SIGNAL_ACTION_STATE_CHANGED] =
 272     g_signal_new (I_("action-state-changed"),
 273                   G_TYPE_ACTION_GROUP,
 274                   G_SIGNAL_RUN_LAST |
 275                   G_SIGNAL_DETAILED |
 276                   G_SIGNAL_MUST_COLLECT,
 277                   G_STRUCT_OFFSET (GActionGroupInterface,
 278                                    action_state_changed),
 279                   NULL, NULL,
 280                   NULL,
 281                   G_TYPE_NONE, 2,
 282                   G_TYPE_STRING,
 283                   G_TYPE_VARIANT);
 284 }
 285
 286 /**
 287  * g_action_group_list_actions:
 288  * @action_group: a #GActionGroup
 289  *
 290  * Lists the actions contained within @action_group.
 291  *
 292  * The caller is responsible for freeing the list with g_strfreev() when
 293  * it is no longer required.
 294  *
 295  * Returns: (transfer full): a %NULL-terminated array of the names of the
 296  * actions in the groupb
 297  *
 298  * Since: 2.28
 299  **/
 300 gchar **
 301 g_action_group_list_actions (GActionGroup *action_group)
 302 {
 303   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), NULL);
 304
 305   return G_ACTION_GROUP_GET_IFACE (action_group)
 306     ->list_actions (action_group);
 307 }
 308
 309 /**
 310  * g_action_group_has_action:
 311  * @action_group: a #GActionGroup
 312  * @action_name: the name of the action to check for
 313  *
 314  * Checks if the named action exists within @action_group.
 315  *
 316  * Returns: whether the named action exists
 317  *
 318  * Since: 2.28
 319  **/
 320 gboolean
 321 g_action_group_has_action (GActionGroup *action_group,
 322                            const gchar  *action_name)
 323 {
 324   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), FALSE);
 325
 326   return G_ACTION_GROUP_GET_IFACE (action_group)
 327     ->has_action (action_group, action_name);
 328 }
 329
 330 /**
 331  * g_action_group_get_action_parameter_type:
 332  * @action_group: a #GActionGroup
 333  * @action_name: the name of the action to query
 334  *
 335  * Queries the type of the parameter that must be given when activating
 336  * the named action within @action_group.
 337  *
 338  * When activating the action using g_action_group_activate_action(),
 339  * the #GVariant given to that function must be of the type returned
 340  * by this function.
 341  *
 342  * In the case that this function returns %NULL, you must not give any
 343  * #GVariant, but %NULL instead.
 344  *
 345  * The parameter type of a particular action will never change but it is
 346  * possible for an action to be removed and for a new action to be added
 347  * with the same name but a different parameter type.
 348  *
 349  * Return value: the parameter type
 350  *
 351  * Since: 2.28
 352  **/
 353 const GVariantType *
 354 g_action_group_get_action_parameter_type (GActionGroup *action_group,
 355                                           const gchar  *action_name)
 356 {
 357   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), NULL);
 358
 359   return G_ACTION_GROUP_GET_IFACE (action_group)
 360     ->get_action_parameter_type (action_group, action_name);
 361 }
 362
 363 /**
 364  * g_action_group_get_action_state_type:
 365  * @action_group: a #GActionGroup
 366  * @action_name: the name of the action to query
 367  *
 368  * Queries the type of the state of the named action within
 369  * @action_group.
 370  *
 371  * If the action is stateful then this function returns the
 372  * #GVariantType of the state.  All calls to
 373  * g_action_group_change_action_state() must give a #GVariant of this
 374  * type and g_action_group_get_action_state() will return a #GVariant
 375  * of the same type.
 376  *
 377  * If the action is not stateful then this function will return %NULL.
 378  * In that case, g_action_group_get_action_state() will return %NULL
 379  * and you must not call g_action_group_change_action_state().
 380  *
 381  * The state type of a particular action will never change but it is
 382  * possible for an action to be removed and for a new action to be added
 383  * with the same name but a different state type.
 384  *
 385  * Returns: (transfer full): the state type, if the action is stateful
 386  *
 387  * Since: 2.28
 388  **/
 389 const GVariantType *
 390 g_action_group_get_action_state_type (GActionGroup *action_group,
 391                                       const gchar  *action_name)
 392 {
 393   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), NULL);
 394
 395   return G_ACTION_GROUP_GET_IFACE (action_group)
 396     ->get_action_state_type (action_group, action_name);
 397 }
 398
 399 /**
 400  * g_action_group_get_action_state_hint:
 401  * @action_group: a #GActionGroup
 402  * @action_name: the name of the action to query
 403  *
 404  * Requests a hint about the valid range of values for the state of the
 405  * named action within @action_group.
 406  *
 407  * If %NULL is returned it either means that the action is not stateful
 408  * or that there is no hint about the valid range of values for the
 409  * state of the action.
 410  *
 411  * If a #GVariant array is returned then each item in the array is a
 412  * possible value for the state.  If a #GVariant pair (ie: two-tuple) is
 413  * returned then the tuple specifies the inclusive lower and upper bound
 414  * of valid values for the state.
 415  *
 416  * In any case, the information is merely a hint.  It may be possible to
 417  * have a state value outside of the hinted range and setting a value
 418  * within the range may fail.
 419  *
 420  * The return value (if non-%NULL) should be freed with
 421  * g_variant_unref() when it is no longer required.
 422  *
 423  * Return value: (transfer full): the state range hint
 424  *
 425  * Since: 2.28
 426  **/
 427 GVariant *
 428 g_action_group_get_action_state_hint (GActionGroup *action_group,
 429                                       const gchar  *action_name)
 430 {
 431   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), NULL);
 432
 433   return G_ACTION_GROUP_GET_IFACE (action_group)
 434     ->get_action_state_hint (action_group, action_name);
 435 }
 436
 437 /**
 438  * g_action_group_get_action_enabled:
 439  * @action_group: a #GActionGroup
 440  * @action_name: the name of the action to query
 441  *
 442  * Checks if the named action within @action_group is currently enabled.
 443  *
 444  * An action must be enabled in order to be activated or in order to
 445  * have its state changed from outside callers.
 446  *
 447  * Return value: whether or not the action is currently enabled
 448  *
 449  * Since: 2.28
 450  **/
 451 gboolean
 452 g_action_group_get_action_enabled (GActionGroup *action_group,
 453                                    const gchar  *action_name)
 454 {
 455   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), FALSE);
 456
 457   return G_ACTION_GROUP_GET_IFACE (action_group)
 458     ->get_action_enabled (action_group, action_name);
 459 }
 460
 461 /**
 462  * g_action_group_get_action_state:
 463  * @action_group: a #GActionGroup
 464  * @action_name: the name of the action to query
 465  *
 466  * Queries the current state of the named action within @action_group.
 467  *
 468  * If the action is not stateful then %NULL will be returned.  If the
 469  * action is stateful then the type of the return value is the type
 470  * given by g_action_group_get_action_state_type().
 471  *
 472  * The return value (if non-%NULL) should be freed with
 473  * g_variant_unref() when it is no longer required.
 474  *
 475  * Return value: (allow-none): the current state of the action
 476  *
 477  * Since: 2.28
 478  **/
 479 GVariant *
 480 g_action_group_get_action_state (GActionGroup *action_group,
 481                                  const gchar  *action_name)
 482 {
 483   g_return_val_if_fail (G_IS_ACTION_GROUP (action_group), NULL);
 484
 485   return G_ACTION_GROUP_GET_IFACE (action_group)
 486     ->get_action_state (action_group, action_name);
 487 }
 488
 489 /**
 490  * g_action_group_change_action_state:
 491  * @action_group: a #GActionGroup
 492  * @action_name: the name of the action to request the change on
 493  * @value: the new state
 494  *
 495  * Request for the state of the named action within @action_group to be
 496  * changed to @value.
 497  *
 498  * The action must be stateful and @value must be of the correct type.
 499  * See g_action_group_get_action_state_type().
 500  *
 501  * This call merely requests a change.  The action may refuse to change
 502  * its state or may change its state to something other than @value.
 503  * See g_action_group_get_action_state_hint().
 504  *
 505  * If the @value GVariant is floating, it is consumed.
 506  *
 507  * Since: 2.28
 508  **/
 509 void
 510 g_action_group_change_action_state (GActionGroup *action_group,
 511                                     const gchar  *action_name,
 512                                     GVariant     *value)
 513 {
 514   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 515   g_return_if_fail (action_name != NULL);
 516   g_return_if_fail (value != NULL);
 517
 518   G_ACTION_GROUP_GET_IFACE (action_group)
 519     ->change_action_state (action_group, action_name, value);
 520 }
 521
 522 /**
 523  * g_action_group_activate_action:
 524  * @action_group: a #GActionGroup
 525  * @action_name: the name of the action to activate
 526  * @parameter: (allow-none): parameters to the activation
 527  *
 528  * Activate the named action within @action_group.
 529  *
 530  * If the action is expecting a parameter, then the correct type of
 531  * parameter must be given as @parameter.  If the action is expecting no
 532  * parameters then @parameter must be %NULL.  See
 533  * g_action_group_get_action_parameter_type().
 534  *
 535  * Since: 2.28
 536  **/
 537 void
 538 g_action_group_activate_action (GActionGroup *action_group,
 539                                 const gchar  *action_name,
 540                                 GVariant     *parameter)
 541 {
 542   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 543   g_return_if_fail (action_name != NULL);
 544
 545   G_ACTION_GROUP_GET_IFACE (action_group)
 546     ->activate_action (action_group, action_name, parameter);
 547 }
 548
 549 /**
 550  * g_action_group_action_added:
 551  * @action_group: a #GActionGroup
 552  * @action_name: the name of an action in the group
 553  *
 554  * Emits the #GActionGroup::action-added signal on @action_group.
 555  *
 556  * This function should only be called by #GActionGroup implementations.
 557  *
 558  * Since: 2.28
 559  **/
 560 void
 561 g_action_group_action_added (GActionGroup *action_group,
 562                              const gchar  *action_name)
 563 {
 564   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 565   g_return_if_fail (action_name != NULL);
 566
 567   g_signal_emit (action_group,
 568                  g_action_group_signals[SIGNAL_ACTION_ADDED],
 569                  g_quark_try_string (action_name),
 570                  action_name);
 571 }
 572
 573 /**
 574  * g_action_group_action_removed:
 575  * @action_group: a #GActionGroup
 576  * @action_name: the name of an action in the group
 577  *
 578  * Emits the #GActionGroup::action-removed signal on @action_group.
 579  *
 580  * This function should only be called by #GActionGroup implementations.
 581  *
 582  * Since: 2.28
 583  **/
 584 void
 585 g_action_group_action_removed (GActionGroup *action_group,
 586                                const gchar  *action_name)
 587 {
 588   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 589   g_return_if_fail (action_name != NULL);
 590
 591   g_signal_emit (action_group,
 592                  g_action_group_signals[SIGNAL_ACTION_REMOVED],
 593                  g_quark_try_string (action_name),
 594                  action_name);
 595 }
 596
 597 /**
 598  * g_action_group_action_enabled_changed:
 599  * @action_group: a #GActionGroup
 600  * @action_name: the name of an action in the group
 601  * @enabled: whether or not the action is now enabled
 602  *
 603  * Emits the #GActionGroup::action-enabled-changed signal on @action_group.
 604  *
 605  * This function should only be called by #GActionGroup implementations.
 606  *
 607  * Since: 2.28
 608  **/
 609 void
 610 g_action_group_action_enabled_changed (GActionGroup *action_group,
 611                                        const gchar  *action_name,
 612                                        gboolean      enabled)
 613 {
 614   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 615   g_return_if_fail (action_name != NULL);
 616
 617   enabled = !!enabled;
 618
 619   g_signal_emit (action_group,
 620                  g_action_group_signals[SIGNAL_ACTION_ENABLED_CHANGED],
 621                  g_quark_try_string (action_name),
 622                  action_name,
 623                  enabled);
 624 }
 625
 626 /**
 627  * g_action_group_action_state_changed:
 628  * @action_group: a #GActionGroup
 629  * @action_name: the name of an action in the group
 630  * @state: the new state of the named action
 631  *
 632  * Emits the #GActionGroup::action-state-changed signal on @action_group.
 633  *
 634  * This function should only be called by #GActionGroup implementations.
 635  *
 636  * Since: 2.28
 637  **/
 638 void
 639 g_action_group_action_state_changed (GActionGroup *action_group,
 640                                      const gchar  *action_name,
 641                                      GVariant     *state)
 642 {
 643   g_return_if_fail (G_IS_ACTION_GROUP (action_group));
 644   g_return_if_fail (action_name != NULL);
 645
 646   g_signal_emit (action_group,
 647                  g_action_group_signals[SIGNAL_ACTION_STATE_CHANGED],
 648                  g_quark_try_string (action_name),
 649                  action_name,
 650                  state);
 651 }
 652
 653 /**
 654  * g_action_group_query_action:
 655  * @action_group: a #GActionGroup
 656  * @action_name: the name of an action in the group
 657  * @enabled: (out): if the action is presently enabled
 658  * @parameter_type: (out): the parameter type, or %NULL if none needed
 659  * @state_type: (out): the state type, or %NULL if stateless
 660  * @state_hint: (out): the state hint, or %NULL if none
 661  * @state: (out): the current state, or %NULL if stateless
 662  *
 663  * Queries all aspects of the named action within an @action_group.
 664  *
 665  * This function acquires the information available from
 666  * g_action_group_has_action(), g_action_group_get_action_enabled(),
 667  * g_action_group_get_action_parameter_type(),
 668  * g_action_group_get_action_state_type(),
 669  * g_action_group_get_action_state_hint() and
 670  * g_action_group_get_state() with a single function call.
 671  *
 672  * This provides two main benefits.
 673  *
 674  * The first is the improvement in efficiency that comes with not having
 675  * to perform repeated lookups of the action in order to discover
 676  * different things about it.  The second is that implementing
 677  * #GActionGroup can now be done by only overriding this one virtual
 678  * function.
 679  *
 680  * The interface provides a default implementation of this function that
 681  * calls the individual functions, as required, to fetch the
 682  * information.  The interface also provides default implementations of
 683  * those functions that call this function.  All implementations,
 684  * therefore, must override either this function or all of the others.
 685  *
 686  * If the action exists, %TRUE is returned and any of the requested
 687  * fields (as indicated by having a non-%NULL reference passed in) are
 688  * filled.  If the action doesn't exist, %FALSE is returned and the
 689  * fields may or may not have been modified.
 690  *
 691  * Returns: %TRUE if the action exists, else %FALSE
 692  *
 693  * Since: 2.32
 694  **/
 695 gboolean
 696 g_action_group_query_action (GActionGroup        *action_group,
 697                              const gchar         *action_name,
 698                              gboolean            *enabled,
 699                              const GVariantType **parameter_type,
 700                              const GVariantType **state_type,
 701                              GVariant           **state_hint,
 702                              GVariant           **state)
 703 {
 704   return G_ACTION_GROUP_GET_IFACE (action_group)
 705     ->query_action (action_group, action_name, enabled, parameter_type, state_type, state_hint, state);
 706 }