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pod::Prima::Object(3) User Contributed Perl Documentationpod::Prima::Object(3)

       Prima::Object - Prima toolkit base classes

	   if (	$obj-> isa('Prima::Component'))	{

	       # set and get a property
	       my $name	= $obj-> name;
	       $obj->name( 'an object' );

	       # set a notification callback
	       $obj-> onPostMessage( sub {
		   print "hey! I've received this: @_\n";

	       # can set multiple properties. note, that 'name'	and 'owner',
	       # replace the old values, while onPostMessage are aggregated.
	       $obj-> set(
		   name	=> 'AnObject',
		   owner => $new_owner,
		   onPostMessage => sub	{
		      print "hey! me too!\n";

	       # de-reference by name
	       $new_owner-> AnObject-> post_message(1,2);

       Prima::Object and Prima::Component are the root objects of the Prima
       toolkit hierarchy. All the other	objects	are derived from the Component
       class, which in turn is the only	descendant of Object class. Both of
       these classes are never used for	spawning their instances, although
       this is possible	using

	  Prima::Component-> create( ..	parameters ... );

       call. This document describes the basic concepts	of the OO programming
       with Prima toolkit. Although Component has wider	functionality than
       Object, all examples will be explained on Component, since Object has
       no descendant classes and all the functionality of Object is present in
       Component.  Some	of the information here	can be found in
       Prima::internals	as well, the difference	is that	Prima::internals
       considers the coding tasks from a C programmer's	view, whereas this
       document	is wholly about	perl programming.

Object base features
       Object creation has fixed syntax:

	  $new_object =	Class->	create(
	    parameter => value,
	    parameter => value,

       Parameters and values form a hash, which	is passed to the create()
       method.	This hash is applied to	a default parameter-value hash ( a
       profile ), specific to every Prima class. The object creation is
       performed in several stages.

	   create() calls profile_default() method that	returns	( as its name
	   states ) the	default	profile, a hash	with the appropriate default
	   values assigned to its keys.	 The Component class defaults are (
	   see ):

		name	    => ref $_[ 0],
		owner	    => $::application,
		delegations => undef,

	   While the exact meaning of these parameters is described later, in
	   "Properties", the idea is that a newly created object will have
	   'owner' parameter set to '$::application' and 'delegations' to
	   undef etc etc - unless these	parameters are explicitly passed to
	   create(). Example:

		$a1 = Prima::Component-> create();

	   $a1's owner will be $::application

		$a2 = Prima::Component-> create( owner => $a1);

	   $a2's owner will be $a1.  The actual	merging	of the default and the
	   parameter hashes is performed on the	next stage, in
	   profile_check_in() method which is called inside profile_add()

	   A profile_check_in()	method merges the default and the parameter
	   profiles. By	default	all specified parameters have the ultimate
	   precedence over the default ones, but in case the specification is
	   incomplete or ambiguous, the	profile_check_in()'s task is to
	   determine actual parameter values. In case of Component, this
	   method maintains a simple automatic naming of the newly created
	   objects. If the object name was not specified with create(),	it is
	   assigned to a concatenated class name with an integer - Component1,
	   Component2 etc.

	   Another example can be taken	from
	   Prima::Widget::profile_check_in().  Prima::Widget horizontal
	   position can	be specified by	using basic "left" and "width"
	   parameters, and as well by auxiliary	"right", "size"	and "rect".
	   The default of both "left" and "width" is 100. But if only "right"
	   parameter, for example, was passed to create() it is
	   profile_check_in() job to determine "left" value, given that
	   "width" is still 100.

	   After profiles gets merged, the resulting hash is passed to the
	   third stage,	init().

	   init() duty is to map the profile content into object, e.g.,	assign
	   "name" property to "name" parameter value, and so on	- for all
	   relevant parameters.	 After that, it	has to return the profile in
	   order the overridden	subsequent init() methods can perform same
	   actions. This stage along with the previous is exemplified in
	   almost all Prima modules.

	   Note: usually init()	attaches the object to its owner in order to
	   keep	the newly-created object instance from being deleted by
	   garbage-collection mechanisms. More on that later ( see "Links
	   between objects").

	   After init()	finishes, create() calls setup() method

	   setup() method is a convenience function, it	is used	when some
	   post-init actions must be taken. It is seldom overloaded, primarily
	   because the Component::setup() method calls "onCreate"
	   notification, which is more convenient to overload than setup().

       As can be noticed from the code pieces above, a successful create()
       call returns a newly created object. If an error	condition occurred,
       undef is	returned. It must be noted, that only errors that were
       generated via die() during init() stage result in undef.	Other errors
       raise an	exception instead.  It is not recommended to frame create()
       calls in	an "eval{}" block, because the error conditions	can only occur
       in two situations. The first is a system	error, either inside perl or
       Prima guts, and not much	can be done here, since	that error can very
       probably	lead to	an unstable program and	almost always signals an
       implementation bug. The second reason is	a caller's error, when an
       unexistent parameter key	or invalid value is passed; such conditions
       are not subject to a runtime error handling as are not the syntax

       After create(), the object is subject to	the event flow.	 As "onCreate"
       event is	the first event	the object receives, only after	that stage
       other events can	be circulated.

       Object destruction can be caused	by many	conditions, but	all execution
       flow is finally passed through destroy()	method.	 destroy(), as well as
       create()	performs several finalizing steps:

	   The first method called inside destroy() is cleanup().  cleanup()
	   is the pair to setup(), as destroy()	is the pair to create().
	   cleanup() generates "onDestroy" event, which	can be overridden more
	   easily than cleanup() itself.

	   "onDestroy" is the last event the object sees. After	cleanup() no
	   events are allowed to circulate.

	   done() method is the	pair to	init(),	and is the place where all
	   object resources are	freed. Although	it is as safe to overload
	   done() as init(), it	almost never gets overloaded, primarily
	   because overloading "onDestroy" is easier.

       The typical conditions that lead	to object destructions are direct
       destroy() call, garbage collections mechanisms, user-initiated window
       close ( on "Prima::Window" only ), and exception	during init() stage.
       Thus, one must be careful implementing done() which is called after
       init() throws an	exception.

       The class methods are declared and used with perl OO syntax, which
       allow both method of object referencing:

	 $object-> method();


	 method( $object);

       The actual code is a sub, located under the object class	package.  The
       overloaded methods that call their ancestor code	use

	 $object-> SUPER::method();

       syntax. Most Prima methods have fixed number of parameters.

       Properties are methods that combine functionality of two	ephemeral
       "get" and "set" methods.	The idea behind	properties is that many	object
       parameters require two independent methods, one that returns some
       internal	state and another that changes it.  For	example, for managing
       the object name,	set_name() and get_name() methods are needed. Indeed,
       the early Prima implementation dealt with large amount of these get's
       and set's, but later these method pairs were deprecated in the favor of
       properties.  Currently, there is	only one method	name() ( referred as
       "::name"	later in the documentation ).

       The property returns a value if no parameters ( except the object) are
       passed, and changes the internal	data to	the passed parameters
       otherwise. Here's a sketch code for "::name" property implementation:

	sub name
	   return $_[0]-> {name} unless	$#_;
	   $_[0]->{name} = $_[1];

       There are many examples of properties throughout	the toolkit.  Not all
       properties deal with scalar values, some	accept arrays or hashes	as
       well.  The properties can be set-called not only	by name	like

	 $object-> name( "new name");

       but also	with set() method. The set() method accepts a hash, that is
       much like to create(), and assigns the values to	the corresponding
       properties. For example,	the code

	 $object-> name( "new name");
	 $object-> owner( $owner);

       can be rewritten	as

	 $object-> set(
	    name  => "new name",
	    owner => $owner

       A minor positive	effect of a possible speed-up is gained	by eliminating
       C-to-perl and perl-to-C calls, especially if the	code called is
       implemented in C. The negative effect of	such technique is that the
       order in	which the properties are set, is undefined. Therefore, the
       usage of	set() is recommended either when the property order is
       irrelevant, or it is known beforehand that such a call speeds up	the
       code, or	is an only way to achieve the result. An example of the	latter
       case from Prima::internals shows	that Prima::Image calls

	   $image-> type( $a);
	   $image-> palette( $b);


	   $image-> palette( $b);
	   $image-> type( $a);

       produce different results. It is	indeed the only	solution to call for
       such a change using

	   $image-> set(
	      type => $a,
	      palette => $b

       when it is known	beforehand that	"Prima::Image::set" is aware of	such
       combinations and	calls neither "::type" nor "::palette" but performs
       another image conversion	instead.

       Some properties are read-only and some are write-only. Some methods
       that might be declared as properties are	not; these are declared	as
       plain methods with get_ or set_ name prefix. There is not much
       certainty about what methods are	better off being declared as
       properties and vice versa.

       However,	if get_	or set_	methods	cannot be used in correspondingly
       write or	read fashion, the R/O and W/O properties can. They raise an
       exception on an attempt to do so.

   Links between objects
       Prima::Component	descendants can	be used	as containers, as objects that
       are on a	higher hierarchy level than the	others.	This scheme is
       implemented in a	child-owner relationship.  The 'children' objects have
       the "::owner" property value assigned to	a reference to a 'owner'
       object, while the 'owner' object	conducts the list of its children. It
       is a one-to-many	hierarchy scheme, as a 'child' object can have only
       one owner, but an 'owner' object	can have many children.	The same
       object can be an	owner and a child at the same time, so the owner-child
       hierarchy can be	viewed as a tree-like structure.

       Prima::Component::owner property	maintains this relation, and is
       writable	- the object can change	its owner dynamically. There is	no
       corresponding property that manages children objects, but is a method
       get_components(), that returns an array of the child references.

       The owner-child relationship is used in several ways in the toolkit.
       For example, the	widgets	that are children of another widget appear (
       usually,	but not	always ) in the	geometrical interior of	the owner
       widget.	Some events ( keyboard events, for example ) are propagated
       automatically up	and/or down the	object tree. Another important feature
       is that when an object gets destroyed, its children are destroyed
       first.  In a typical program the	whole object tree roots	in a
       Prima::Application object instance. When	the application	finishes, this
       feature helps cleaning up the widgets and quitting gracefully.

       Implementation note: name 'owner' was taken instead of initial
       'parent', because the 'parent' is a fixed term for widget hierarchy
       relationship description. Prima::Widget relationship between owner and
       child is	not the	same as	GUI's parent-to-child.	The parent is the
       widget for the children widgets located in and clipped by its inferior.
       The owner widget	is more	than that, its children	can be located outside
       its owner boundaries.

       The special convenience variety of create(), the	insert() method	is
       used to explicitly select owner of the newly created object. insert()
       can be considered a 'constructor' in OO-terms. It makes the construct

	  $obj = Class-> create( owner => $owner, name => 'name);

       more readable by	introducing

	  $obj = $owner-> insert( 'Class', name	=> 'name');

       scheme. These two code blocks are identical to each other.

       There is	another	type of	relation, where	objects	can hold references to
       each other. Internally this link	level is used to keep objects from
       deletion	by garbage collection mechanisms.  This	relation is many-to-
       many scheme, where every	object can have	many links to other objects.
       This functionality is managed by	attach() and detach() methods.

       Prima::Component	descendants employ a well-developed event propagation
       mechanism, which	allows handling	events using several different
       schemes.	 An event is a condition, caused by the	system or the user, or
       an explicit notify() call. The formerly described events	onCreate and
       onDestroy are triggered after a new object is created or	before it gets
       destroyed. These	two events, and	the described below onPostMessage are
       present in namespaces of	all Prima objects.  New	classes	can register
       their own events	and define their execution flow, using
       notification_types() method.  This method returns all available
       information about the events registered in a class.

       Prima defines also a non-object event dispatching and filtering
       mechanism, available through "event_hook" static	method.

       The event propagation mechanism has three layers	of user-defined
       callback	registration, that are called in different order and contexts
       when an event is	triggered. The examples	below show the usage of	these
       layers. It is assumed that an implicit

	 $obj->	notify("PostMessage", $data1, $data2);

       call is issued for all these examples.

       Direct methods
	   As it is usual in OO	programming, event callback routines are
	   declared as methods.	'Direct	methods' employ	such a paradigm, so if
	   a class method with name "on_postmessage" is	present, it will be
	   called as a method (	i.e., in the object context ) when
	   "onPostMessage" event is triggered. Example:

	    sub	on_postmessage
	       my ( $self, $data1, $data2) = @_;

	   The callback	name is	a modified lower-case event name: the name for
	   Create event	is on_create, PostMessage - on_postmessage etc.	 These
	   methods can be overloaded in	the object's class descendants.	 The
	   only	note on	declaring these	methods	in the first instance is that
	   no "::SUPER"	call is	needed,	because	these methods are not defined
	   by default.

	   Usually the direct methods are used for the internal	object book-
	   keeping, reacting on	the events that	are not	designed to be passed
	   higher. For example,	a Prima::Button	class catches mouse and
	   keyboard events in such a fashion, because usually the only
	   notification	that is	interesting for	the code that employs push-
	   buttons is "Click".	This scheme is convenient when an event
	   handling routine serves the internal, implementation-specific

       Delegated methods
	   The delegated methods are used when objects ( mostly	widgets	)
	   include other dependent objects, and	the functionality requires
	   interaction between these.  The callback functions here are the
	   same	methods	as direct methods, except that they get	called in
	   context of two, not one, objects. If, for example, a	$obj's owner,
	   $owner would	be interested in $obj's	PostMessage event, it would
	   register the	notification callback by

	      $obj-> delegations([ $owner, 'PostMessage']);

	   where the actual callback sub will be

	    sub	Obj_PostMessage
	       my ( $self, $obj, $data1, $data2) = @_;

	   Note	that the naming	style is different - the callback name is
	   constructed from object name	( let assume that $obj's name is
	   'Obj') and the event	name. (	This is	one of the reasons why
	   Component::profile_check_in() performs automatic naming of newly
	   created onbjects). Note also	that context objects are $self ( that
	   equals $owner ) and $obj.

	   The delegated methods can be	used not only for the owner-child
	   relations. Every Prima object is free to add	a delegation method to
	   every other object. However,	if the objects are in other than
	   owner-child relation, it is a good practice to add Destroy
	   notification	to the object which events are of interest, so if it
	   gets	destroyed, the partner object gets a message about that.

       Anonymous subroutines
	   The two previous callback types are more relevant when a separate
	   class is developed, but it is not necessary to declare a new	class
	   every time the event	handling is needed.  It	is possible to use the
	   third and the most powerful event hook method using perl anonymous
	   subroutines ( subs )	for the	easy customization.

	   Contrary to the usual OO event implementations, when	only one
	   routine per class dispatches	an event, and calls inherited handlers
	   when	it is appropriate, Prima event handling	mechanism can accept
	   many	event handlers for one object (	it is greatly facilitated by
	   the fact that perl has anonymous subs, however).

	   All the callback routines are called	when an	event is triggered,
	   one by one in turn. If the direct and delegated methods can only be
	   multiplexed by the usual OO inheritance, the	anonymous subs are
	   allowed to be multiple by the design.  There	are three syntaxes for
	   setting such	a event	hook; the example below	sets a hook on $obj
	   using each syntax for a different situation:

	   - during create():

	      $obj = Class-> create(
	       onPostMessage =>	sub {
		  my ( $self, $data1, $data2) =	@_;

	   - after create using	set()

	      $obj-> set( onPostMessage	=> sub {
		  my ( $self, $data1, $data2) =	@_;

	   - after create using	event name:

	      $obj-> onPostMessage( sub	{
		  my ( $self, $data1, $data2) =	@_;

	   As was noted	in Prima, the events can be addressed as properties,
	   with	the exception that they	are not	substitutive but additive.
	   The additivity is that when the latter type of syntax is used, the
	   subs	already	registered do not get overwritten or discarded but
	   stack in queue. Thus,

	      $obj-> onPostMessage( sub	{ print	"1" });
	      $obj-> onPostMessage( sub	{ print	"2" });
	      $obj-> notify( "PostMessage", 0, 0);

	   code	block would print


	   as the execution result.

	   This, it is a distinctive feature of	a toolkit is that two objects
	   of same class may have different set	of event handlers.

       When there is more than one handler of a	particular event type present
       on an object, a question	is risen about what are	callbacks call
       priorities and when does	the event processing stop. One of ways to
       regulate	the event flow is based	on prototyping events, by using
       notification_types() event type description.  This function returns a
       hash, where keys	are the	event names and	the values are the constants
       that describe the event flow. The constant can be a bitwise OR
       combination of several basic flow constants, that control the three
       aspects of the event flow.

	   If both anonymous subs and direct/delegated methods are present, it
	   must	be decided which callback class	must be	called first.  Both
	   'orders' are	useful:	for example, if	it is designed that a class's
	   default action is to	be overridden, it is better to call the	custom
	   actions first. If, on the contrary, the class action	is primary,
	   and the others are supplementary, the reverse order is preferred.
	   One of two "nt::PrivateFirst" and "nt::CustomFirst" constants
	   defines the order.

	   Almost the same as order, but for finer granulation of event	flow,
	   the direction constants "nt::FluxNormal" and	"nt::FluxReverse" are
	   used. The 'normal flux' defines FIFO	( first	in first out )
	   direction. That means, that the sooner the callback is registered,
	   the greater priority	it would possess during	the execution.	The
	   code	block shown above

	      $obj-> onPostMessage( sub	{ print	"1" });
	      $obj-> onPostMessage( sub	{ print	"2" });
	      $obj-> notify( "PostMessage", 0, 0);

	   results in 21, not 12 because PostMessage event type	is prototyped

       Execution control
	   It was stated above that the	events are additive, - the callback
	   storage is never discarded  when 'set'-syntax is used.  However,
	   the event can be told to behave like	a substitutive property, e.g.
	   to call one and only	one callback.  This functionality is governed
	   by "nt::Single" bit in execution control constant set, which
	   consists of the following constants:


	   These constants are mutually	exclusive, and may not appear together
	   in an event type declaration.  A "nt::Single"-prototyped
	   notification	calls only the first ( or the last - depending on
	   order and direction bits ) callback.	The usage of this constant is
	   somewhat limited.

	   In contrary of "nt::Single",	the "nt::Multiple" constant sets the
	   execution control to	call all the available callbacks, with respect
	   to direction	and order bits.

	   The third constant, "nt::Event", is the  impact as "nt::Multiple",
	   except that the event flow can be stopped at	any time by calling
	   clear_event() method.

       Although	there are 12 possible event type combinations, a half of them
       are not viable. Another half were assigned to unique more-less
       intelligible names:

	 nt::Default	   ( PrivateFirst | Multiple | FluxReverse)
	 nt::Property	   ( PrivateFirst | Single   | FluxNormal )
	 nt::Request	   ( PrivateFirst | Event    | FluxNormal )
	 nt::Notification  ( CustomFirst  | Multiple | FluxReverse )
	 nt::Action	   ( CustomFirst  | Single   | FluxReverse )
	 nt::Command	   ( CustomFirst  | Event    | FluxReverse )

   Success state
       Events do not return values, although the event generator, the notify()
       method does - it	returns	either 1 or 0, which is	the value of event
       success state.  The 0 and 1 results in general do not mean either
       success or failure, they	simply reflect the fact	whether	clear_event()
       method was called during	the processing - 1 if it was not, 0 otherwise.
       The state is kept during	the whole processing stage, and	can be
       accessed	from Component::eventFlag property. Since it is	allowed	to
       call notify() inside event callbacks, the object	maintains a stack for
       those states.  Component::eventFlags always works with the topmost one,
       and fails if is called from outside the event processing	stage.
       Actually, clear_event() is an alias for ::eventFlag(0) call. The	state
       stack is	operated by push_event() and pop_event() methods.

       Implementation note: a call of clear_event() inside a
       "nt::Event"-prototyped event call does not automatically	stops the
       execution. The execution	stops if the state value equals	to 0 after the
       callback	is finished.  A	::eventFlag(1) call thus cancels the effect of

       A particular coding style is used when the event	is
       "nt::Single"-prototyped and is called many times	in a row, so overheads
       of calling notify() become a burden. Although notify() logic is
       somewhat	complicated, it	is rather simple with "nt::Single" case. The
       helper function get_notify_sub()	returns	the context of callback	to-be-
       called, so it can be used to emulate notify() behavior.	Example:

	 for ( ... ) {
	    $result = $obj-> notify( "Measure",	@parms);

       can be expressed	in more	cumbersome, but	efficient code if
       "nt::Single"-prototyped event is	used:

	  my ( $notifier, @notifyParms)	= $obj-> get_notify_sub( "Measure" );
	  $obj-> push_event;
	  for (	... ) {
	      $notifier-> ( @notifyParms, @parms);
	      #	$result	= $obj-> eventFlag; # this is optional
	  $result = $obj-> pop_event;

   Prima::Object methods
	   Returns the object 'vitality' state - true if the object is alive
	   and usable, false otherwise.	 This method can be used as a general
	   checkout if the scalar passed is a Prima object, and	if it is
	   usable.  The	true return value can be 1 for normal and operational
	   object state, and 2 if the object is	alive but in its init()	stage.

	     print $obj-> name if Prima::Object::alive(	$obj);

	   Called right	after destroy()	started. Used to initiate "cmDestroy"
	   event. Is never called directly.

       create CLASS, %PARAMETERS
	   Creates a new object	instance of a given CLASS and sets its
	   properties corresponding to the passed parameter hash. Examples:

	      $obj = Class-> create( PARAMETERS);
	      $obj = Prima::Object::create( "class" , PARAMETERS);

	   Is never called in an object	context.

	   Alias: new()

	   Initiates the object	destruction. Perform in	turn cleanup() and
	   done() calls.  destroy() can	be called several times	and is the
	   only	Prima re-entrant function, therefore may not be	overloaded.

	   Called by destroy() after cleanup() is finished. Used to free the
	   object resources, as	a finalization stage.  During done() no	events
	   are allowed to circulate, and alive() returns 0. The	object is not
	   usable after	done() finishes. Is never called directly.

	   Note: the eventual child objects are	destroyed inside done()	call.

       get @PARAMETERS
	   Returns hash	where keys are @PARAMETERS and values are the
	   corresponding object	properties.

       init %PARAMETERS
	   The most important stage of object creation process.	 %PARAMETERS
	   is the modified hash	that was passed	to create().  The modification
	   consists of merging with the	result of profile_default() class
	   method inside profile_check_in() method. init() is responsible for
	   applying the	relevant data into PARAMETERS to the object
	   properties. Is never	called directly.

       insert CLASS, %PARAMETERS
	   A convenience wrapper for create(), that explicitly sets the	owner
	   property for	a newly	created	object.

	      $obj = $owner-> insert( 'Class', name => 'name');

	   is adequate to

	      $obj = Class-> create( owner => $owner, name => 'name);

	   code. insert() has another syntax that allows simultaneous creation
	   of several objects:

	      @objects = $owner-> insert(
		[ 'Class', %parameters],
		[ 'Class', %parameters],

	   With	such syntax, all newly created objects would have $owner set
	   to their 'owner' properties.

	   Same	as create.

       profile_add PROFILE
	   The first stage of object creation process.	PROFILE	is a reference
	   to a	PARAMETERS hash, passed	to create().  It is merged with
	   profile_default() after passing both	to profile_check_in(). The
	   merge result	is stored back in PROFILE.  Is never called directly.

       profile_check_in	CUSTOM_PROFILE,	DEFAULT_PROFILE
	   The second stage of object creation process.	 Resolves eventual
	   ambiguities in CUSTOM_PROFILE, which	is the reference to PARAMETERS
	   passed to create(), by comparing to and using default values	from
	   DEFAULT_PROFILE, which is the result	of profile_default() method.
	   Is never called directly.

	   Returns hash	of the appropriate default values for all properties
	   of a	class.	In object creation process serves as a provider	of
	   fall-back values, and is called implicitly. This method can be used
	   directly, contrary to the other creation process-related functions.

	   Can be called in a context of class.

       raise_ro	TEXT
	   Throws an exception with text TEXT when a read-only property	is
	   called in a set- context.

       raise_wo	TEXT
	   Throws an exception with text TEXT when a write-only	property is
	   called in a get- context.

       set %PARAMETERS
	   The default behavior	is an equivalent to

	     sub set
		my $obj	= shift;
		my %PARAMETERS = @_;
		$obj-> $_( $PARAMETERS{$_}) for	keys %PARAMETERS;

	   code. Assigns object	properties correspondingly to PARAMETERS hash.
	   Many	Prima::Component descendants overload set() to make it more
	   efficient for particular parameter key patterns.

	   As the code above, raises an	exception if the key in	PARAMETERS has
	   no correspondent object property.

	   The last stage of object creation process.  Called after init()
	   finishes. Used to initiate "cmCreate" event.	Is never called

   Prima::Component methods
       add_notification	NAME, SUB, REFERER = undef, INDEX = -1
	   Adds	SUB to the list	of notification	of event NAME.	REFERER	is the
	   object reference, which is used to create a context to SUB and is
	   passed as a parameter to it when called.  If	REFERER	is undef ( or
	   not specified ), the	same object is assumed.	REFERER	also gets
	   implicitly attached to the object, -	the implementation frees the
	   link	between	objects	when one of these gets destroyed.

	   INDEX is a desired insert position in the notification list.	 By
	   default it is -1, what means	'in the	start'.	If the notification
	   type	contains nt::FluxNormal	bit set, the newly inserted SUB	will
	   be called first. If it has nt::FluxReverse, it is called last,

	   Returns positive integer value on success, 0	on failure.  This
	   value can be	later used to refer to the SUB in

	   See also: "remove_notification", "get_notification".

       attach OBJECT
	   Inserts OBJECT to the attached objects list and increases OBJECT's
	   reference count. The	list can not hold more than one	reference to
	   the same object. The	warning	is issued on such an attempt.

	   See also: "detach".

       bring NAME
	   Looks for a immediate child object that has name equals to NAME.
	   Returns its reference on success, undef otherwise. It is a
	   convenience method, that makes possible the usage of	the following

	      $obj-> name( "Obj");
	      $obj-> owner( $owner);
	      $owner-> Obj-> destroy;

	   See also: "find_component"

	   Returns true	if the object event circulation	is allowed.  In
	   general, the	same as	"alive() == 1",	except that can_event()	fails
	   if an invalid object	reference is passed.

	   Clears the event state, that	is set to 1 when the event processing
	   begins.  Signals the	event execution	stop for nt::Event-prototyped

	   See also: "Events", "push_event", "pop_event", "::eventFlag",

       detach OBJECT, KILL
	   Removes OBJECT from the attached objects list and decreases
	   OBJECT's reference count. If	KILL is	true, destroys OBJECT.

	   See also: "attach"

	   Issues a system-dependent warning sound signal.

       event_hook [ SUB	]
	   Installs a SUB to receive all events	on all Prima objects.  SUB
	   receives same parameters passed to notify, and must return an
	   integer, either 1 or	0, to pass or block the	event respectively.

	   If no SUB is	set, returns currently installed event hook pointer.
	   If SUB is set, replaces the old hook	sub with SUB. If SUB is
	   'undef', event filtering is not used.

	   Since the 'event_hook' mechanism allows only	one hook routine to be
	   installed at	a time,	direct usage of	the method is discouraged.
	   Instead, use	Prima::EventHook for multiplexing of the hook access.

	   The method is static, and can be called either with or without
	   class or object as a	first parameter.

       find_component NAME
	   Performs a depth-first search on children tree hierarchy, matching
	   the object that has name equal to NAME.  Returns its	reference on
	   success, undef otherwise.

	   See also: "bring"

	   Returns array of the	child objects.

	   See:	"create", "Links between objects".

	   Returns a system-dependent handle for the object.  For example,
	   Prima::Widget return	its system WINDOW/HWND handles,
	   Prima::DeviceBitmap - its system PIXMAP/HBITMAP handles, etc.

	   Can be used to pass the handle value	outside	the program, for an
	   eventual interprocess communication scheme.

       get_notification	NAME, @INDEX_LIST
	   For each index in INDEX_LIST	return three scalars, bound at the
	   index position in the NAME event notification list.	These three
	   scalars are REFERER,	SUB and	ID. REFERER and	SUB are	those passed
	   to "add_notification", and ID is its	result.

	   See also: "remove_notification", "add_notification".

       get_notify_sub NAME
	   A convenience method	for nt::Single-prototyped events.  Returns
	   code	reference and context for the first notification sub for event

	   See "Success	state" for example.

	   Returns a hash, where the keys are the event	names and the values
	   are the "nt::" constants that describe the event flow.

	   Can be called in a context of class.

	   See "Events"	and "Flow" for details.

       notify NAME, @PARAMETERS
	   Calls the subroutines bound to the event NAME with parameters
	   @PARAMETERS in context of the object.  The calling order is
	   described by	"nt::" constants, contained in the
	   notification_types()	result hash.

	   notify() accepts variable number of parameters, and while it	is
	   possible, it	is not recommended to call notify() with the exceeding
	   number of parameters; the call with the deficient number of
	   parameters results in an exception.


	      $obj-> notify( "PostMessage", 0, 1);

	   See "Events"	and "Flow" for details.

	   Closes event	processing stage brackets.

	   See "push_event", "Events"

       post_message SCALAR1, SCALAR2
	   Calls "PostMessage" event with parameters SCALAR1 and SCALAR2 once
	   during idle event loop. Returns immediately.	 Does not guarantee
	   that	"PostMessage" will be called, however.

	   See also "post" in Prima::Utils

	   Opens event processing stage	brackets.

	   See "pop_event", "Events"

       remove_notification ID
	   Removes a notification subroutine that was registered before	with
	   "add_notification", where ID	was its	result.	After successful
	   removal, the	eventual context object	gets implicitly	detached from
	   the storage object.

	   See also: "add_notification", "get_notification".

       set_notification	NAME, SUB
	   Adds	SUB to the event NAME notification list. Almost	never used
	   directly, but is a key point	in enabling the	following notification
	   add syntax

	      $obj-> onPostMessage( sub	{ ... });


	      $obj-> set( onPostMessage	=> sub { ... });

	   that	are shortcuts for

	      $obj-> add_notification( "PostMessage", sub { ...	});

       unlink_notifier REFERER
	   Removes all notification subs from all event	lists bound to REFERER

   Prima::Component properties
       eventFlag STATE
	   Provides access to the last event processing	state in the object
	   event state stack.

	   See also: "Success state", "clear_event", "Events".

       delegations [ <REFERER>,	NAME, <NAME>, <	<REFERER>, NAME, ... > ]
	   Accepts an anonymous	array in set- context, which consists of a
	   list	of event NAMEs,	that a REFERER object (	the caller object by
	   default ) is	interested in.	Registers notification entries for
	   routines if subs with naming	scheme REFERER_NAME are	present	on
	   REFERER name	space.	The example code

	      $obj-> name("Obj");
	      $obj-> delegations([ $owner, 'PostMessage']);

	   registers Obj_PostMessage callback if it is present in $owner

	   In get- context returns an array reference that reflects the
	   object's delegated events list content.

	   See also: "Delegated	methods".

       name NAME
	   Maintains object name. NAME can be an arbitrary string, however it
	   is recommended against usage	of special characters and spaces in
	   NAME, to facilitate the indirect object access coding style:

	      $obj-> name( "Obj");
	      $obj-> owner( $owner);
	      $owner-> Obj-> destroy;

	   and to prevent system-dependent issues. If the system provides
	   capabilities	that allow to predefine	some object parameters by its
	   name	( or class), then it is	impossible to know beforehand the
	   system naming restrictions.	For example, in	X window system	the
	   following resource string would make	all Prima toolkit buttons

	     Prima*Button*backColor: green

	   In this case, using special characters such as ":" or "*" in	the
	   name	of an object would make	the X resource unusable.

       owner OBJECT
	   Selects an owner of the object, which may be	any Prima::Component
	   descendant.	Setting	an owner to a object does not alter its
	   reference count. Some classes allow OBJECT to be undef, while some
	   do not. All widget objects can not exist without a valid owner;
	   Prima::Application on the contrary can only exist with owner	set to
	   undef. Prima::Image objects are indifferent to the value of the
	   owner property.

	   Changing owner dynamically is allowed, but it is a main source of
	   implementation bugs,	since the whole	hierarchy tree is needed to be
	   recreated.  Although	this effect is not visible in perl, the
	   results are deeply system-dependent,	and the	code that changes
	   owner property should be thoroughly tested.

	   Changes to "owner" result in	up to three notifications:
	   "ChangeOwner", which	is called to the object	itself,	"ChildLeave",
	   which notifies the previous owner that the object is	about to
	   leave, and "ChildEnter", telling the	new owner about	the new	child.

   Prima::Component events
       ChangeOwner OLD_OWNER
	   Called at runtime when the object changes its owner.

       ChildEnter CHILD
	   Triggered when a child object is attached, either as	a new instance
	   or as a result of runtime owner change.

       ChildLeave CHILD
	   Triggered when a child object is detached, either because it	is
	   getting destroyed or	as a result of runtime owner change.

	   The first event an event sees. Called automatically after init() is
	   finished.  Is never called directly.

	   The last event an event sees. Called	automatically before done() is
	   started.  Is	never called directly.

       PostMessage SCALAR1, SCALAR2
	   Called after	post_message() call is issued, not inside
	   post_message() but at the next idle event loop.  SCALAR1 and
	   SCALAR2 are the data	passed to post_message().

	   Sometimes Prima needs to implicitly re-create the system handle of
	   a component.	 The re-creation is not	seen on	the toolkit level,
	   except for some repaints when widgets on screen are affected, but
	   under the hood, when	it happens, Prima creates a whole new system
	   resource. This happens when the underlying system either doesn't
	   have	API to change a	certain	property during	the runtime, or	when
	   such	a re-creation happens on one of	component's parent, leading to
	   a downward cascade of children re-creation. Also, it	may happen
	   when	the user changes some system settings resolution, so that some
	   resources have to be	changed	accordingly.

	   This	event will be only needed when the system handle (that can be
	   acquired by "get_handle" ) is used further, or in case when Prima
	   doesn't restore some	properties bound to the	system handle.

       Dmitry Karasik, <>.

       Prima, Prima::internals,	Prima::EventHook.

perl v5.24.1			  2017-02-28		 pod::Prima::Object(3)

NAME | SYNOPSIS | DESCRIPTION | Object base features | Events | API | AUTHOR | SEE ALSO

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