glib/docs/reference/gobject/tmpl/signals.sgml

<!-- ##### SECTION Title ##### -->
Signals

<!-- ##### SECTION Short_Description ##### -->
Signals provide a means for customization of object behaviour and are used
as general purpose notification mechanism.

<!-- ##### SECTION Long_Description ##### -->
<para>
The basic concept of the signal system is that of the @emission of a signal.
Signals are introduced per-type and are identified through strings.
Signals introduced for a parent type are availale in derived types as well,
so basically they are a per-type facility that is inherited.
A signal emission mainly involves invocation of a certain set of callbacks in
precisely defined manner. There are two main categories of such callbacks,
per-object
	<footnote><para> Although signals can deal with any kind of type, i'm
	referring to those types as "@object @types" in the following, simply
	because that is the context most users will encounter signals in.
	</para></footnote>
ones and user provided ones.
The per-object callbacks are most often referred to as "object method
handler" or "default (signal) handler", while user provided callbacks are
usually just called "signal handler".
The object method handler is provided at signal creation time (this most
frequently happens at the end of an object class' creation), while user
provided handlers are frequently @connected and @disconnected to/from a certain
signal on certain object instances.
</para>
<para>
A signal emission consists of five stages, unless prematurely stopped:
<variablelist>
  <varlistentry><term></term><listitem><para>
	1 - Invocation of the object method handler for @G_SIGNAL_RUN_FIRST signals
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	2 - Invocation of normal user-provided signal handlers (@after flag @FALSE)
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	3 - Invocation of the object method handler for @G_SIGNAL_RUN_LAST signals
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	4 - Invocation of user provided signal handlers, connected with an @after flag of @TRUE
  </para></listitem></varlistentry>
  <varlistentry><term></term><listitem><para>
	5 - Invocation of the object method handler for @G_SIGNAL_RUN_CLEANUP signals
  </para></listitem></varlistentry>
</variablelist>
The user provided signal handlers are called in the order they were
connected in.
All handlers may prematurely stop a signal emission, and any number of
handlers may be connected, disconnected, blocked or unblocked during
a signal emission.
There are certain criteria for skipping user handlers in stages 2 and 4
of a signal emission.
First, user handlers may be @blocked, blocked handlers are omitted
during callback invocation, to return from the "blocked" state, a
handler has to get unblocked exactly the same amount of times
it has been blocked before.
Second, upon emission of a @G_SIGNAL_DETAILED signal, an additional
"detail" argument passed in to g_signal_emit() has to match the detail
argument of the signal handler currently subject to invocation.
Specification of no detail argument for signal handlers (omission of the
detail part of the signal specification upon connection) serves as a
wildcard and matches any detail argument passed in to emission.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### STRUCT GSignalInvocationHint ##### -->
<para>
The @GSignalInvocationHint structure is used to pass on additional information
to callbacks during a signal emission.
</para>

@signal_id:	The signal id of the signal invoking the callback
@detail:	The detail passed on for this emission
@run_type:	The stage the signal emission is currently in, this
		field will contain one of @G_SIGNAL_RUN_FIRST,
		@G_SIGNAL_RUN_LAST or @G_SIGNAL_RUN_CLEANUP.

<!-- ##### USER_FUNCTION GSignalAccumulator ##### -->
<para>
The signal accumulator is a special callback function that can be used
to collect return values of the various callbacks that are called
during a signal emission. The signal accumulator is specified at signal
creation time, if it is left NULL, no accumulation of callback return
values is perfomed. The return value of signal emissions is then the
value returned by the last callback.
</para>

@ihint:		Signal invokation hint, see @GSignalInvocationHint
@return_accu:	Accumulator to collect callback return values in, this
		is the return value of the current signal emission
@return_value:	The return value of the most recent callback function
@Returns:	The accumulator function returns whether the signal emission
		should be aborted. Returning @FALSE means to abort the
		current emission and @TRUE is returned for continuation.


<!-- ##### TYPEDEF GSignalCMarshaller ##### -->
<para>

</para>


<!-- ##### USER_FUNCTION GSignalEmissionHook ##### -->
<para>

</para>

@ihint: 
@n_param_values: 
@param_values: 
@Returns: 
<!-- # Unused Parameters # -->
@signal_id: 
@n_values: 
@values: 


<!-- ##### ENUM GSignalFlags ##### -->
<para>

</para>

@G_SIGNAL_RUN_FIRST: 
@G_SIGNAL_RUN_LAST: 
@G_SIGNAL_RUN_CLEANUP: 
@G_SIGNAL_NO_RECURSE: 
@G_SIGNAL_DETAILED: 
@G_SIGNAL_ACTION: 
@G_SIGNAL_NO_HOOKS: 

<!-- ##### ENUM GSignalMatchType ##### -->
<para>

</para>

@G_SIGNAL_MATCH_ID: 
@G_SIGNAL_MATCH_DETAIL: 
@G_SIGNAL_MATCH_CLOSURE: 
@G_SIGNAL_MATCH_FUNC: 
@G_SIGNAL_MATCH_DATA: 
@G_SIGNAL_MATCH_UNBLOCKED: 

<!-- ##### STRUCT GSignalQuery ##### -->
<para>
A structure holding in-depth information for a specific signal. It is
filled in by the g_signal_query() function.
</para>

@signal_id:	The signal id of the signal being querried, or 0 if the
		signal to be querried was unknown
@signal_name:	The signal name
@itype:		The interface/instance type that this signal can be emitted for
@signal_flags:	The signal flags as passed in to @g_signal_new()
@return_type:	The return type for user callbacks
@n_params:	The number of parameters that user callbacks take
@param_types:	The individual parameter types for user callbacks, note that the
		effective callback signature is:
<msgtext><programlisting>
@return_type callback (@gpointer     data1,
                      [@param_types param_names,]
                      @gpointer     data2);
</programlisting></msgtext>

<!-- ##### FUNCTION g_signal_newv ##### -->
<para>

</para>

@signal_name: 
@itype: 
@signal_flags: 
@class_closure: 
@accumulator: 
@c_marshaller: 
@return_type: 
@n_params: 
@param_types: 
@Returns: 


<!-- ##### FUNCTION g_signal_emitv ##### -->
<para>

</para>

@instance_and_params: 
@signal_id: 
@detail: 
@return_value: 


<!-- ##### FUNCTION g_signal_lookup ##### -->
<para>

</para>

@name: 
@itype: 
@Returns: 


<!-- ##### FUNCTION g_signal_name ##### -->
<para>

</para>

@signal_id: 
@Returns: 


<!-- ##### FUNCTION g_signal_query ##### -->
<para>
Query the signal system for in-depth information about a
specific signal. This function will fill in a user-provided
structure to hold signal-specific information. If an invalid
dignal id is passed in, the @signal_id member of the @GSignalQuery
is 0. All members filled into the @GSignalQuery structure should
be considered constant and have to be left untouched.
</para>

@signal_id:	The signal id of the signal to query information for
@query:		A user provided structure that is filled in with constant
		values upon success.


<!-- ##### FUNCTION g_signal_list_ids ##### -->
<para>
List the signals by id, that a certain instance or interface type
created. Further information about the signals can be aquired through
g_signal_query().
</para>

@itype:		Instance or interface type
@n_ids:		Location to store the number of signal ids for @itype
@Returns:	Newly allocated array of signal ids


<!-- ##### FUNCTION g_signal_connect_closure ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@closure: 
@after: 
@Returns: 


<!-- ##### FUNCTION g_signal_handler_find ##### -->
<para>

</para>

@instance: 
@mask: 
@signal_id: 
@detail: 
@closure: 
@func: 
@data: 
@Returns: 


<!-- ##### FUNCTION g_signal_handler_block ##### -->
<para>

</para>

@instance: 
@handler_id: 


<!-- ##### FUNCTION g_signal_handler_unblock ##### -->
<para>

</para>

@instance: 
@handler_id: 


<!-- ##### FUNCTION g_signal_handler_disconnect ##### -->
<para>

</para>

@instance: 
@handler_id: 


<!-- ##### FUNCTION g_signal_has_handler_pending ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 
@may_be_blocked: 
@Returns: 


<!-- ##### FUNCTION g_signal_stop_emission ##### -->
<para>

</para>

@instance: 
@signal_id: 
@detail: 


<!-- ##### FUNCTION g_signal_type_closure_new ##### -->
<para>

</para>

@itype: 
@struct_offset: 
@Returns: 


<!-- ##### FUNCTION g_signal_add_emission_hook_full ##### -->
<para>

</para>

@signal_id: 
@closure: 
@Returns: 


<!-- ##### FUNCTION g_signal_remove_emission_hook ##### -->
<para>

</para>

@signal_id: 
@hook_id: 


<!-- ##### FUNCTION g_signal_handlers_destroy ##### -->
<para>

</para>

@instance: 


<!-- ##### FUNCTION g_signals_destroy ##### -->
<para>

</para>

@itype: