/ 
Object-Event-1.101
River stage two • 17 direct dependents • 38 total dependents
/ Object::Event

NAME

Object::Event - A class that provides an event callback interface

VERSION

Version 1.101

SYNOPSIS

package foo;
use Object::Event;

our @ISA = qw/Object::Event/;

package main;
my $o = foo->new;

my $regguard = $o->reg_cb (foo => sub {
   print "I got an event, with these args: $_[1], $_[2], $_[3]\n";
});

$o->event (foo => 1, 2, 3);

$o->unreg_cb ($regguard);
# or just:
$regguard = undef;

DESCRIPTION

This module was mainly written for AnyEvent::XMPP, AnyEvent::IRC, AnyEvent::HTTPD and BS to provide a consistent API for registering and emitting events. Even though I originally wrote it for those modules I released it separately in case anyone may find this module useful.

For more comprehensive event handling see also Glib and POE.

This class provides a simple way to extend a class, by inheriting from this class, with an event callback interface.

You will be able to register callbacks for events, identified by their names (a string) and call them later by invoking the event method with the event name and some arguments.

There is even a syntactic sugar which allows to call methods on the instances of a from Object::Event-derived class, to invoke events. See enable_methods below. For this feature please also consult the test cases in the distribution for examples.

PERFORMANCE

In the first version as presented here no special performance optimisations have been applied. So take care that it is fast enough for your purposes. At least for modules like AnyEvent::XMPP the overhead is probably not noticeable, as other technologies like XML already waste a lot more CPU cycles. Also I/O usually introduces _much_ larger/longer overheads than this simple event interface.

FUNCTIONS

Object::Event::register_priority_alias ($alias, $priority)

This package function will add a global priority alias. If $priority is undef the alias will be removed.

There are 4 predefined aliases:

before     =>  1000
ext_before =>   500
ext_after  =>  -500
after      => -1000

See also the reg_cb method for more information about aliases.

METHODS

Object::Event->new (%args)
Your::Subclass::Of::Object::Event->new (%args)

This is the constructor for Object::Event, it will create a blessed hash reference initialized with %args.

There are these special keys for %args:

enable_methods => $bool

If $bool is a true value this object will overwrite the methods in it's package with event emitting methods, and add the method's code as priority 0 event callback. The replacement will happen whenever an event callback is registered with reg_cb.

$obj->init_object_events ()

This method should only be called if you are not able to call the new constructor of this class.

$obj->set_exception_cb ($cb->($exception, $eventname))

This method installs a callback that will be called when some other event callback threw an exception. The first argument to $cb will be the exception and the second the event name.

$guard = $obj->reg_cb ($eventname => $cb->($obj, @args), ...)
$guard = $obj->reg_cb ($eventname => $prio, $cb->($obj, @args), ...)

This method registers a callback $cb1 for the event with the name $eventname1. You can also pass multiple of these eventname => callback pairs.

The return value will be an ID that represents the set of callbacks you have installed. Call unreg_cb with that ID to remove those callbacks again.

The first argument for callbacks registered with the reg_cb function will always be the master object $obj. If you want to have the event object $ev (which represents an event which was sent by the event method) as first argument use the reg_event_cb method.

The return value of the callbacks are ignored. If you need to pass any information from a handler to the caller of the event you have to establish your own "protocol" to do this. I recommend to pass an array reference to the handlers:

$obj->reg_cb (event_foobar => sub {
   my ($self, $results) = @_;
   push @$results, time / 30;
});

my @results;
$obj->event (event_foobar => \@results);
for (@results) {
   # ...
}

The order of the callbacks in the call chain of the event depends on their priority. If you didn't specify any priority (see below) they get the default priority of 0, and are appended to the other priority 0 callbacks. The higher the priority number, the earlier the callbacks gets called in the chain.

If $eventname1 starts with 'before_' the callback gets a priority of 1000, and if it starts with 'ext_before_' it gets the priority 500. 'after_' is mapped to the priority -1000 and 'ext_after_' to -500.

If you want more fine grained control you can pass an array reference instead of the event name:

($eventname1, $prio) = ('test_abc', 100);
$obj->reg_cb ([$eventname1, $prio] => sub {
   ...
});
$obj->unreg_cb ($cb)

Removes the callback $cb from the set of registered callbacks.

$obj->event ($eventname, @args)

Emits the event $eventname and passes the arguments @args to the callbacks. The return value is a true value in case some handler was found and run. It returns false if no handler was found (see also the handles method below). Basically: It returns the same value as the handles method.

Please note that an event can be stopped and reinvoked while it is being handled.

See also the specification of the before and after events in reg_cb above.

NOTE: Whenever an event is emitted the current set of callbacks registered to that event will be used. So, if you register another event callback for the same event that is executed at the moment, it will be called the next time when the event is emitted. Example:

$obj->reg_cb (event_test => sub {
   my ($obj) = @_;

   print "Test1\n";
   $obj->unreg_me;

   $obj->reg_cb (event_test => sub {
      my ($obj) = @_;
      print "Test2\n";
      $obj->unreg_me;
   });
});

$obj->event ('event_test'); # prints "Test1"
$obj->event ('event_test'); # prints "Test2"
my $bool = $obj->handles ($eventname)

This method returns true if any event handler (either registered via reg_cb or by a method definition if enable_methods is enabled) has been setup for the event $eventname.

It returns false if that is not the case.

$obj->event_name

Returns the name of the currently executed event.

$obj->unreg_me

Unregisters the currently executed callback.

$continue_cb = $obj->stop_event

This method stops the execution of callbacks of the current event, and returns (in non-void context) a callback that will let you continue the execution.

$obj->add_forward ($obj, $cb)

DEPRECATED: Don't use it! Just for backward compatibility for AnyEvent::XMPP version 0.4.

$obj->remove_forward ($obj)

DEPRECATED: Don't use it! Just for backward compatibility for AnyEvent::XMPP version 0.4.

$obj->remove_all_callbacks ()

This method removes all registered event callbacks from this object.

$obj->events_as_string_dump ()

This method returns a string dump of all registered event callbacks. This method is only for debugging purposes.

__PACKAGE__->hand_event_methods_down ($eventname, ...);

NOTE: This is only of interest to you if you enabled enable_methods.

If you want to build up a class hierarchy of Object::Event classes which pass down the defined event methods for events, you need to call this package method. It will pack up all given $eventnames for subclasses, which can 'inherit' these with the inherit_event_methods_from package method (see below).

Because the event methods of a package are global with regard to the object instances they need to be added to, you need to register them for the subclasses.

NOTE: If you want to hand down event methods from super-classes make sure you call inherit_event_methods_from BEFORE hand_event_methods_down!

NOTE: For an example about how to use this see the test case t/15_methods_subc.t.

__PACKAGE__->hand_event_methods_down_from ($package, ...);

NOTE: This is only of interest to you if you enabled enable_methods.

This is a sugar method for hand_event_methods_down, which will hand down all event methods of the packages in the argument list, along with the in the current package overridden event method.

NOTE: For an example about how to use this see the test case t/15_methods_subc.t.

__PACKAGE__->inherit_event_methods_from ('SUPER_PKG1', 'OTHER_SUPER', ...)

NOTE: This is only of interest to you if you enabled enable_methods.

Call this package method if you want to inherit event methods from super packages, which you have to give as argument list.

NOTE: For an example about how to use this see the test case t/15_methods_subc.t.

AUTHOR

Robin Redeker, <elmex at ta-sa.org>, JID: <elmex at jabber.org>

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc Object::Event

You can also look for information at:

ACKNOWLEDGEMENTS

Thanks go to:

- Mons Anderson for suggesting the 'handles' method and
  the return value of the 'event' method and reporting bugs.

COPYRIGHT & LICENSE

Copyright 2009 Robin Redeker, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.