NAME¶
Prima::Object - Prima toolkit base classes
SYNOPSIS¶
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 {
shift;
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 {
shift;
print "hey! me too!\n";
},
);
# de-reference by name
$new_owner-> AnObject-> post_message(1,2);
}
DESCRIPTION¶
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¶
Creation¶
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
- 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
Classes.pm ):
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() method.
- profile_check_in
- 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
- 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
- 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 errors.
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.
Destruction¶
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:
- cleanup
- 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
- 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.
Methods¶
The class methods are declared and used with perl OO syntax, which allow both
method of object referencing:
$object-> method();
and
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¶
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);
and
$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.
Events¶
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.
Propagation¶
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 needs.
- 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
21
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.
Flow¶
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.
- Order
- 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.
- Direction
- 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
"nt::FluxReverse".
- 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:
nt::Single
nt::Multiple
nt::Event
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
clear_event().
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;
API¶
Prima::Object methods¶
- alive
- 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. Example:
print $obj-> name if Prima::Object::alive( $obj);
- can NAME, CACHE = 1
- Checks if an object namespace contains a NAME method. Returns the code
reference to it, if found, and undef if not. If CACHE is true, caches the
result to speed-up subsequent calls.
- cleanup
- 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()
- destroy
- 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.
- done
- 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.
- new CLASS, %PARAMETERS
- 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.
- profile_default
- 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.
- setup
- The last stage of object creation process. Called after init()
finishes. Used to initiate "cmCreate" event. Is never called
directly.
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, correspondingly.
Returns positive integer value on success, 0 on failure. This value can be
later used to refer to the SUB in remove_notification().
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 constructs:
$obj-> name( "Obj");
$obj-> owner( $owner);
...
$owner-> Obj-> destroy;
- can_event
- 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.
- clear_event
- Clears the event state, that is set to 1 when the event processing begins.
Signals the event execution stop for nt::Event-prototyped events.
See also: "Events", "push_event", "pop_event",
"::eventFlag", "notify".
- 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"
- event_error
- 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.
- get_components
- Returns array of the child objects.
See: "create", "Links between objects".
- get_handle
- 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 NAME.
See "Success state" for example.
- notification_types
- 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.
Example:
$obj-> notify( "PostMessage", 0, 1);
See "Events" and "Flow" for details.
- pop_event
- 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
- push_event
- 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 { ... });
or
$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
object.
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 namespace.
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 green:
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.
- Create
- The first event an event sees. Called automatically after init() is
finished. Is never called directly.
- Destroy
- 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().
AUTHOR¶
Dmitry Karasik, <dmitry@karasik.eu.org>.
SEE ALSO¶
Prima, Prima::internals, Prima::EventHook.