PHP: How to realize event handler? - php

Question

I want to add custom event handler to object's method.
I've got a class with method.
class Post {
public function Add($title) {
// beforeAdd event should be called here
echo 'Post "' . $title . '" added.';
return;
}
}
I want to add an event to method Add and pass method's argument(s) to the event handler.
function AddEventHandler($event, $handler){
// What should this function do?
}
$handler = function($title){
return strtoupper($title);
}
AddEventHandler('beforeAdd', $handler);
Is it possible to do something like this? Hope my question is clear.

Answer 1

Should be pretty easy using the functions defined here http://www.php.net/manual/en/book.funchand.php
In particular you should keep an handler array (or array of arrays if you want multiple handlers for the same event) and then just do something like
function AddEventHandler($event, $handler){
$handlerArray[$event] = $handler;
}
or
function AddEventHandler($event, $handler){
$handlerArray[$event][] = $handler;
}
in case of multiple handlers.
Invoking the handlers then would be just matter of calling "call_user_func" (eventually in a cycle if multiple handlers are needed)

Answer 2

Well, if you are using < php 5.3 then you cannot create a closure in such a way, but you can come close with create_function(); This would be
$handler = create_function('$title', 'return strtoupper($title);');
Then you store $handler in the class and you can call it as you desire.

Answer 3

Methods
You have multiple methods how to do it described by ircmaxell here.
And here is ToroHook used in ToroPHP (Routing lib).
Hook
class ToroHook {
private static $instance;
private $hooks = array();
private function __construct() {}
private function __clone() {}
public static function add($hook_name, $fn){
$instance = self::get_instance();
$instance->hooks[$hook_name][] = $fn;
}
public static function fire($hook_name, $params = null){
$instance = self::get_instance();
if (isset($instance->hooks[$hook_name])) {
foreach ($instance->hooks[$hook_name] as $fn) {
call_user_func_array($fn, array(&$params));
}
}
}
public static function remove($hook_name){
$instance = self::get_instance();
unset($instance->hooks[$hook_name]);
var_dump($instance->hooks);
}
public static function get_instance(){
if (empty(self::$instance)) {
self::$instance = new Hook();
}
return self::$instance;
}
}
Using hook
It is simple call it like this:
ToroHook::add('404', function($errorpage){
render("page/not_found", array("errorpage" => $errorpage));
});

Answer 4

Take look on my sphido/events library:
it's easy to use (few lines of code)
based on PHP Function handling
allow prioritising listeners
add/remove listeners
filter values by functions
stop propagation in function chain
add default handler
Event handler example
on('event', function () {
echo "wow it's works yeah!";
});
fire('event'); // print wow it's works yeah!
Filter function example
add_filter('price', function($price) {
return (int)$price . ' USD';
});
echo filter('price', 100); // print 100 USD