docs/reference/gobject/tmpl/signals.sgml

   1 <!-- ##### SECTION Title ##### -->
   2 Signals
   3
   4 <!-- ##### SECTION Short_Description ##### -->
   5 Signals provide a means for customization of object behaviour and are used
   6 as general purpose notification mechanism.
   7
   8 <!-- ##### SECTION Long_Description ##### -->
   9 <para>
  10 The basic concept of the signal system is that of the <emphasis>emission</emphasis>
  11 of a signal.
  12 Signals are introduced per-type and are identified through strings.
  13 Signals introduced for a parent type are availale in derived types as well,
  14 so basically they are a per-type facility that is inherited.
  15 A signal emission mainly involves invocation of a certain set of callbacks in
  16 precisely defined manner. There are two main categories of such callbacks,
  17 per-object
  18         <footnote><para> Although signals can deal with any kind of instantiatable type,
  19         i'm referring to those types as "object types" in the following, simply
  20         because that is the context most users will encounter signals in.
  21         </para></footnote>
  22 ones and user provided ones.
  23 The per-object callbacks are most often referred to as "object method
  24 handler" or "default (signal) handler", while user provided callbacks are
  25 usually just called "signal handler".
  26 The object method handler is provided at signal creation time (this most
  27 frequently happens at the end of an object class' creation), while user
  28 provided handlers are frequently connected and disconnected to/from a certain
  29 signal on certain object instances.
  30 </para>
  31 <para>
  32 A signal emission consists of five stages, unless prematurely stopped:
  33 <variablelist>
  34   <varlistentry><term></term><listitem><para>
  35         1 - Invocation of the object method handler for %G_SIGNAL_RUN_FIRST signals
  36   </para></listitem></varlistentry>
  37   <varlistentry><term></term><listitem><para>
  38         2 - Invocation of normal user-provided signal handlers (<emphasis>after</emphasis> flag %FALSE)
  39   </para></listitem></varlistentry>
  40   <varlistentry><term></term><listitem><para>
  41         3 - Invocation of the object method handler for %G_SIGNAL_RUN_LAST signals
  42   </para></listitem></varlistentry>
  43   <varlistentry><term></term><listitem><para>
  44         4 - Invocation of user provided signal handlers, connected with an <emphasis>after</emphasis> flag of %TRUE
  45   </para></listitem></varlistentry>
  46   <varlistentry><term></term><listitem><para>
  47         5 - Invocation of the object method handler for %G_SIGNAL_RUN_CLEANUP signals
  48   </para></listitem></varlistentry>
  49 </variablelist>
  50 The user provided signal handlers are called in the order they were
  51 connected in.
  52 All handlers may prematurely stop a signal emission, and any number of
  53 handlers may be connected, disconnected, blocked or unblocked during
  54 a signal emission.
  55 There are certain criteria for skipping user handlers in stages 2 and 4
  56 of a signal emission.
  57 First, user handlers may be <emphasis>blocked</emphasis>, blocked handlers are omitted
  58 during callback invocation, to return from the "blocked" state, a
  59 handler has to get unblocked exactly the same amount of times
  60 it has been blocked before.
  61 Second, upon emission of a %G_SIGNAL_DETAILED signal, an additional
  62 "detail" argument passed in to g_signal_emit() has to match the detail
  63 argument of the signal handler currently subject to invocation.
  64 Specification of no detail argument for signal handlers (omission of the
  65 detail part of the signal specification upon connection) serves as a
  66 wildcard and matches any detail argument passed in to emission.
  67 </para>
  68
  69 <!-- ##### SECTION See_Also ##### -->
  70 <para>
  71
  72 </para>
  73
  74 <!-- ##### STRUCT GSignalInvocationHint ##### -->
  75 <para>
  76 The #GSignalInvocationHint structure is used to pass on additional information
  77 to callbacks during a signal emission.
  78 </para>
  79
  80 @signal_id:     The signal id of the signal invoking the callback
  81 @detail:        The detail passed on for this emission
  82 @run_type:      The stage the signal emission is currently in, this
  83                 field will contain one of %G_SIGNAL_RUN_FIRST,
  84                 %G_SIGNAL_RUN_LAST or %G_SIGNAL_RUN_CLEANUP.
  85
  86 <!-- ##### USER_FUNCTION GSignalAccumulator ##### -->
  87 <para>
  88 The signal accumulator is a special callback function that can be used
  89 to collect return values of the various callbacks that are called
  90 during a signal emission. The signal accumulator is specified at signal
  91 creation time, if it is left NULL, no accumulation of callback return
  92 values is perfomed. The return value of signal emissions is then the
  93 value returned by the last callback.
  94 </para>
  95
  96 @ihint:         Signal invokation hint, see #GSignalInvocationHint.
  97 @return_accu:   Accumulator to collect callback return values in, this
  98                 is the return value of the current signal emission.
  99 @handler_return:
 100 @data:
 101 @Returns:       The accumulator function returns whether the signal emission
 102                 should be aborted. Returning %FALSE means to abort the
 103                 current emission and %TRUE is returned for continuation.
 104 <!-- # Unused Parameters # -->
 105 @return_value:  The return value of the most recent callback function.
 106
 107
 108 <!-- ##### TYPEDEF GSignalCMarshaller ##### -->
 109 <para>
 110 This is the signature of marshaller functions, required to marshall
 111 arrays of parameter values to signal emissions into C language callback
 112 invocations. It is merely an alias to #GClosureMarshal since the #GClosure
 113 mechanism takes over responsibility of actuall function invocation for the
 114 signal system.
 115 </para>
 116
 117
 118 <!-- ##### USER_FUNCTION GSignalEmissionHook ##### -->
 119 <para>
 120
 121 </para>
 122
 123 @ihint:
 124 @n_param_values:
 125 @param_values:
 126 @data:
 127 @Returns:
 128 <!-- # Unused Parameters # -->
 129 @signal_id:
 130 @n_values:
 131 @values:
 132
 133
 134 <!-- ##### ENUM GSignalFlags ##### -->
 135 <para>
 136 The signal flags are used to specify a signal's behaviour, the overrall
 137 signal description outlines how especially the RUN flags controll the
 138 stages of a signal emission.
 139 </para>
 140
 141 @G_SIGNAL_RUN_FIRST:   Invoke the object method handler in the first emission stage.
 142 @G_SIGNAL_RUN_LAST:    Invoke the object method handler in the third emission stage.
 143 @G_SIGNAL_RUN_CLEANUP: Invoke the object method handler in the last emission stage.
 144 @G_SIGNAL_NO_RECURSE:  Signals being emitted for an object while currently being in
 145                        emission for this very object will not be emitted recursively,
 146                        but instead cause the first emission to be restarted.
 147 @G_SIGNAL_DETAILED:    This signal supports "::detail" appendixes to the signal name
 148                        upon hanlder connections and emissions.
 149 @G_SIGNAL_ACTION:      Action signals are signals that may freely be emitted on alive
 150                        objects from user code via g_signal_emit() and friends, without
 151                        the need of being embedded into extra code that performs pre or
 152                        post emission adjustments on the object. They can also be thought
 153                        of as by third-party code generically callable obejct methods.
 154 @G_SIGNAL_NO_HOOKS:    No emissions hooks are supported for this signal.
 155
 156 <!-- ##### ENUM GSignalMatchType ##### -->
 157 <para>
 158
 159 </para>
 160
 161 @G_SIGNAL_MATCH_ID:
 162 @G_SIGNAL_MATCH_DETAIL:
 163 @G_SIGNAL_MATCH_CLOSURE:
 164 @G_SIGNAL_MATCH_FUNC:
 165 @G_SIGNAL_MATCH_DATA:
 166 @G_SIGNAL_MATCH_UNBLOCKED:
 167
 168 <!-- ##### STRUCT GSignalQuery ##### -->
 169 <para>
 170 A structure holding in-depth information for a specific signal. It is
 171 filled in by the g_signal_query() function.
 172 </para>
 173
 174 @signal_id:     The signal id of the signal being querried, or 0 if the
 175                 signal to be querried was unknown.
 176 @signal_name:   The signal name.
 177 @itype:         The interface/instance type that this signal can be emitted for.
 178 @signal_flags:  The signal flags as passed in to g_signal_new().
 179 @return_type:   The return type for user callbacks.
 180 @n_params:      The number of parameters that user callbacks take.
 181 @param_types:   The individual parameter types for user callbacks, note that the
 182                 effective callback signature is:
 183 <msgtext><programlisting>
 184 @return_type callback (#gpointer     data1,
 185                       [#param_types param_names,]
 186                        #gpointer     data2);
 187 </programlisting></msgtext>
 188
 189 <!-- ##### MACRO G_SIGNAL_TYPE_STATIC_SCOPE ##### -->
 190 <para>
 191
 192 </para>
 193
 194
 195
 196 <!-- ##### MACRO G_SIGNAL_MATCH_MASK ##### -->
 197 <para>
 198
 199 </para>
 200
 201
 202
 203 <!-- ##### MACRO G_SIGNAL_FLAGS_MASK ##### -->
 204 <para>
 205
 206 </para>
 207
 208
 209
 210 <!-- ##### MACRO g_signal_newc ##### -->
 211 <para>
 212
 213 </para>
 214
 215 @Returns:
 216 <!-- # Unused Parameters # -->
 217 @signal_name:
 218 @itype:
 219 @signal_flags:
 220 @class_offset:
 221 @accumulator:
 222 @accu_data:
 223 @c_marshaller:
 224 @return_type:
 225 @n_params:
 226 @Varargs:
 227
 228
 229 <!-- ##### FUNCTION g_signal_newv ##### -->
 230 <para>
 231
 232 </para>
 233
 234 @signal_name:
 235 @itype:
 236 @signal_flags:
 237 @class_closure:
 238 @accumulator:
 239 @accu_data:
 240 @c_marshaller:
 241 @return_type:
 242 @n_params:
 243 @param_types:
 244 @Returns:
 245
 246
 247 <!-- ##### FUNCTION g_signal_new_valist ##### -->
 248 <para>
 249
 250 </para>
 251
 252 @signal_name:
 253 @itype:
 254 @signal_flags:
 255 @class_closure:
 256 @accumulator:
 257 @accu_data:
 258 @c_marshaller:
 259 @return_type:
 260 @n_params:
 261 @args:
 262 @Returns:
 263
 264
 265 <!-- ##### FUNCTION g_signal_query ##### -->
 266 <para>
 267 Query the signal system for in-depth information about a
 268 specific signal. This function will fill in a user-provided
 269 structure to hold signal-specific information. If an invalid
 270 dignal id is passed in, the @signal_id member of the #GSignalQuery
 271 is 0. All members filled into the #GSignalQuery structure should
 272 be considered constant and have to be left untouched.
 273 </para>
 274
 275 @signal_id:     The signal id of the signal to query information for.
 276 @query:         A user provided structure that is filled in with constant
 277                 values upon success.
 278
 279
 280 <!-- ##### FUNCTION g_signal_lookup ##### -->
 281 <para>
 282
 283 </para>
 284
 285 @name:
 286 @itype:
 287 @Returns:
 288
 289
 290 <!-- ##### FUNCTION g_signal_name ##### -->
 291 <para>
 292
 293 </para>
 294
 295 @signal_id:
 296 @Returns:
 297
 298
 299 <!-- ##### FUNCTION g_signal_list_ids ##### -->
 300 <para>
 301 List the signals by id, that a certain instance or interface type
 302 created. Further information about the signals can be aquired through
 303 g_signal_query().
 304 </para>
 305
 306 @itype:         Instance or interface type.
 307 @n_ids:         Location to store the number of signal ids for @itype.
 308 @Returns:       Newly allocated array of signal IDs.
 309
 310
 311 <!-- ##### FUNCTION g_signal_emit ##### -->
 312 <para>
 313
 314 </para>
 315
 316 @instance:
 317 @signal_id:
 318 @detail:
 319 @Varargs:
 320
 321
 322 <!-- ##### FUNCTION g_signal_emit_by_name ##### -->
 323 <para>
 324
 325 </para>
 326
 327 @instance:
 328 @detailed_signal:
 329 @Varargs:
 330
 331
 332 <!-- ##### FUNCTION g_signal_emitv ##### -->
 333 <para>
 334
 335 </para>
 336
 337 @instance_and_params:
 338 @signal_id:
 339 @detail:
 340 @return_value:
 341
 342
 343 <!-- ##### FUNCTION g_signal_emit_valist ##### -->
 344 <para>
 345
 346 </para>
 347
 348 @instance:
 349 @signal_id:
 350 @detail:
 351 @var_args:
 352
 353
 354 <!-- ##### FUNCTION g_signal_connect_data ##### -->
 355 <para>
 356
 357 </para>
 358
 359 @instance:
 360 @detailed_signal:
 361 @c_handler:
 362 @data:
 363 @destroy_data:
 364 @connect_flags:
 365 @Returns:
 366 <!-- # Unused Parameters # -->
 367 @swapped:
 368 @after:
 369
 370
 371 <!-- ##### FUNCTION g_signal_connect_object ##### -->
 372 <para>
 373
 374 </para>
 375
 376 @instance:
 377 @detailed_signal:
 378 @c_handler:
 379 @gobject:
 380 @connect_flags:
 381 @Returns:
 382 <!-- # Unused Parameters # -->
 383 @swapped:
 384 @after:
 385
 386
 387 <!-- ##### FUNCTION g_signal_connect_closure ##### -->
 388 <para>
 389
 390 </para>
 391
 392 @instance:
 393 @detailed_signal:
 394 @closure:
 395 @after:
 396 @Returns:
 397 <!-- # Unused Parameters # -->
 398 @signal_id:
 399 @detail:
 400
 401
 402 <!-- ##### FUNCTION g_signal_connect_closure_by_id ##### -->
 403 <para>
 404
 405 </para>
 406
 407 @instance:
 408 @signal_id:
 409 @detail:
 410 @closure:
 411 @after:
 412 @Returns:
 413
 414
 415 <!-- ##### FUNCTION g_signal_handler_block ##### -->
 416 <para>
 417 g_signal_handler_block() blocks a handler of an
 418 instance so it will not be called during any signal emissions
 419 unless it is unblocked again. Thus "blocking" a signal handler
 420 means to temporarily deactive it, a signal handler has to be
 421 unblocked exactly the same amount of times it has been blocked
 422 before to become active again.
 423 The @handler_id passed into g_signal_handler_block() has
 424 to be a valid signal handler id, connected to a signal of
 425 @instance.
 426 </para>
 427
 428 @instance:      The instance to block the signal handler of.
 429 @handler_id:    Handler id of the handler to be blocked.
 430
 431
 432 <!-- ##### FUNCTION g_signal_handler_unblock ##### -->
 433 <para>
 434 g_signal_handler_unblock() undoes the effect of a previous
 435 g_signal_handler_block() call. A blocked handler is skipped
 436 during signal emissions and will not be invoked, unblocking
 437 it (for exactly the amount of times it has been blocked before)
 438 reverts its "blocked" state, so the handler will be recognized
 439 by the signal system and is called upon future or currently
 440 ongoing signal emissions (since the order in which handlers are
 441 called during signal emissions is deterministic, whether the
 442 unblocked handler in question is called as part of a currently
 443 ongoing emission depends on how far that emission has proceeded
 444 yet).
 445 The @handler_id passed into g_signal_handler_unblock() has
 446 to be a valid id of a signal handler that is connected to a
 447 signal of @instance and is currently blocked.
 448 </para>
 449
 450 @instance:      The instance to unblock the signal handler of.
 451 @handler_id:    Handler id of the handler to be unblocked.
 452
 453
 454 <!-- ##### FUNCTION g_signal_handler_disconnect ##### -->
 455 <para>
 456 g_signal_handler_disconnect() disconnects a handler from an
 457 instance so it will not be called during any future or currently
 458 ongoing emissions of the signal it has been connected to.
 459 The @handler_id becomes invalid and may be reused.
 460 The @handler_id passed into g_signal_handler_disconnect() has
 461 to be a valid signal handler id, connected to a signal of
 462 @instance.
 463 </para>
 464
 465 @instance:      The instance to remove the signal handler from.
 466 @handler_id:    Handler id of the handler to be disconnected.
 467
 468
 469 <!-- ##### FUNCTION g_signal_handler_find ##### -->
 470 <para>
 471 Find the first signal handler that matches certain selection criteria.
 472 The criteria mask is passed as an OR-ed combination of #GSignalMatchType
 473 flags, and the criteria values are passed as arguments.
 474 The match @mask has to be non-0 for successfull matches.
 475 If no handler was found, 0 is returned.
 476 </para>
 477
 478 @instance:      The instance owning the signal handler to be found.
 479 @mask:          Mask indicating which of @signal_id, @detail,
 480                 @closure, @func and/or @data the handler has to match.
 481 @signal_id:     Signal the handler has to be connected to.
 482 @detail:        Signal detail the handler has to be connected to.
 483 @closure:       The closure the handler will invoke.
 484 @func:          The C closure callback of the handler (useless for non-C closures).
 485 @data:          The closure data of the handler's closure.
 486 @Returns:       A valid non-0 signal handler id for a successfull match.
 487
 488
 489 <!-- ##### FUNCTION g_signal_handlers_block_matched ##### -->
 490 <para>
 491 This function blocks all handlers on an instance that match a certain
 492 selection criteria. The criteria mask is passed as an OR-ed combination of
 493 #GSignalMatchType flags, and the criteria values are passed as arguments.
 494 Passing at least one of the %G_SIGNAL_MATCH_CLOSURE, %G_SIGNAL_MATCH_FUNC
 495 or %G_SIGNAL_MATCH_DATA match flags is required for successfull matches.
 496 If no handlers were found, 0 is returned, the number of blocked handlers
 497 otherwise.
 498 </para>
 499
 500 @instance:      The instance to block handlers from.
 501 @mask:          Mask indicating which of @signal_id, @detail,
 502                 @closure, @func and/or @data the handlers have to match.
 503 @signal_id:     Signal the handlers have to be connected to.
 504 @detail:        Signal detail the handlers have to be connected to.
 505 @closure:       The closure the handlers will invoke.
 506 @func:          The C closure callback of the handlers (useless for non-C closures).
 507 @data:          The closure data of the handlers' closures.
 508 @Returns:       The amount of handlers that got blocked.
 509
 510
 511 <!-- ##### FUNCTION g_signal_handlers_unblock_matched ##### -->
 512 <para>
 513 This function unblocks all handlers on an instance that match a certain
 514 selection criteria. The criteria mask is passed as an OR-ed combination of
 515 #GSignalMatchType flags, and the criteria values are passed as arguments.
 516 Passing at least one of the %G_SIGNAL_MATCH_CLOSURE, %G_SIGNAL_MATCH_FUNC
 517 or %G_SIGNAL_MATCH_DATA match flags is required for successfull matches.
 518 If no handlers were found, 0 is returned, the number of unblocked handlers
 519 otherwise. The match criteria should not apply to any handlers that are
 520 not currently blocked.
 521 </para>
 522
 523 @instance:      The instance to unblock handlers from.
 524 @mask:          Mask indicating which of @signal_id, @detail,
 525                 @closure, @func and/or @data the handlers have to match.
 526 @signal_id:     Signal the handlers have to be connected to.
 527 @detail:        Signal detail the handlers have to be connected to.
 528 @closure:       The closure the handlers will invoke.
 529 @func:          The C closure callback of the handlers (useless for non-C closures).
 530 @data:          The closure data of the handlers' closures.
 531 @Returns:       The amount of handlers that got unblocked.
 532
 533
 534 <!-- ##### FUNCTION g_signal_handlers_disconnect_matched ##### -->
 535 <para>
 536 This function disconnects all handlers on an instance that match a certain
 537 selection criteria. The criteria mask is passed as an OR-ed combination of
 538 #GSignalMatchType flags, and the criteria values are passed as arguments.
 539 Passing at least one of the %G_SIGNAL_MATCH_CLOSURE, %G_SIGNAL_MATCH_FUNC
 540 or %G_SIGNAL_MATCH_DATA match flags is required for successfull matches.
 541 If no handlers were found, 0 is returned, the number of disconnected handlers
 542 otherwise.
 543 </para>
 544
 545 @instance:      The instance to remove handlers from.
 546 @mask:          Mask indicating which of @signal_id, @detail,
 547                 @closure, @func and/or @data the handlers have to match.
 548 @signal_id:     Signal the handlers have to be connected to.
 549 @detail:        Signal detail the handlers have to be connected to.
 550 @closure:       The closure the handlers will invoke.
 551 @func:          The C closure callback of the handlers (useless for non-C closures).
 552 @data:          The closure data of the handlers' closures.
 553 @Returns:       The amount of handlers that got disconnected.
 554
 555
 556 <!-- ##### FUNCTION g_signal_has_handler_pending ##### -->
 557 <para>
 558
 559 </para>
 560
 561 @instance:
 562 @signal_id:
 563 @detail:
 564 @may_be_blocked:
 565 @Returns:
 566
 567
 568 <!-- ##### FUNCTION g_signal_stop_emission ##### -->
 569 <para>
 570
 571 </para>
 572
 573 @instance:
 574 @signal_id:
 575 @detail:
 576
 577
 578 <!-- ##### FUNCTION g_signal_remove_emission_hook ##### -->
 579 <para>
 580
 581 </para>
 582
 583 @signal_id:
 584 @hook_id:
 585
 586
 587 <!-- ##### FUNCTION g_signal_parse_name ##### -->
 588 <para>
 589 Internal function to parse a signal names into its @signal_id
 590 and @detail quark.
 591 </para>
 592
 593 @detailed_signal:       A string of the form "signal-name::detail".
 594 @itype:                 The interface/instance type that introduced "signal-name".
 595 @signal_id_p:           Location to store the signal id.
 596 @detail_p:              Location to stroe the detail quark.
 597 @force_detail_quark:    %TRUE forces creation of a GQuark for the detail.
 598 @Returns:               Whether the signal name could successfully be parsed and
 599                         @signal_id_p and @detail_p contain valid return values.
 600
 601
 602 <!-- ##### FUNCTION g_signal_handlers_destroy ##### -->
 603 <para>
 604
 605 </para>
 606
 607 @instance:
 608
 609
 610 <!-- ##### FUNCTION g_signal_type_cclosure_new ##### -->
 611 <para>
 612
 613 </para>
 614
 615 @itype:
 616 @struct_offset:
 617 @Returns:
 618
 619