How to implement website plug-in mechanism in php_PHP tutorial

/**
* STBLOG PluginManager Class
*
* Implementation core class of plug-in mechanism
*
* @package STBLOG
* @subpackage Libraries
* @category Libraries
* @author Saturn
* @link http://www.cnsaturn.com/
*/
class PluginManager
{
/**
* Listen for registered plug-ins
*
* @access private
* @var array
*/
private $_listeners = array();
/**
* Constructor
*
* @access public
* @return void
*/
public function __construct()
{
#Here the $plugin array contains the plug-in information we obtain that has been activated by the user
#For the convenience of demonstration, we assume that $plugin contains at least
#$plugin = array (
# 'name' => 'Plug-in name',
# 'directory' => 'Plug-in installation directory'
#);
$plugins = get_active_plugins();#This function Please implement it yourself
if($plugins)
{
foreach($plugins as $plugin)
{//Assume that each plug-in folder contains an actions.php file, which is the plug-in's Specific implementation
if (@file_exists(STPATH ​​.'plugins/'.$plugin['directory'].'/actions.php'))
{
include_once(STPATH ​​.'plugins/'.$ plugin['directory'].'/actions.php');
$class = $plugin['name'].'_actions';
if (class_exists($class))
{
//Initialize all plug-ins
new $class($this);
}
}
}
}
#Do some logging stuff here
}

/**
* Register the plug-in method (hook) that needs to be monitored
*
* @param string $hook
* @param object $reference
* @param string $method
*/
function register($hook, &$reference, $method)
{
//Get the method to be implemented by the plug-in
$key = get_class($reference).'->'.$method;
//Push the plug-in reference and the method into the listening array
$this->_listeners[$hook][$key] = array(&$reference, $method);
#Do some logging stuff here
}
/**
* Trigger a hook
*
* @param string $hook The name of the hook
* @param mixed $data The input parameters of the hook
* @return mixed
*/
function trigger($hook, $data= '')
{
$result = '';
//Check whether the hook to be implemented is in the listening array
if (isset($this->_listeners[$hook] ) && is_array($this->_listeners[$hook]) && count($this->_listeners[$hook]) > 0)
{
// Start of loop call
foreach ( $this->_listeners[$hook] as $listener)
{
// Get the reference and method of the plug-in object
$class =& $listener[0];
$method = $ listener[1];
if(method_exists($class,$method))
{
// Dynamically call the plug-in method
$result .= $class->$method($data );
}
}
}
#Do some logging stuff here
return $result;
}
}
?>

/**
* This is an implementation of a Hello World simple plug-in
*
* @package DEMO
* @subpackage DEMO
* @category Plugins
* @author Saturn
* @ link http://www.cnsaturn.com/
*/
/**
* Several default rules to note:
* 1. The file name of this plug-in class must be action
* 2. The name of the plug-in class must be {plugin name_actions}
*/
class DEMO_actions
{
//The parameter of the parsing function is a reference to pluginManager
function __construct( &$pluginManager)
{
//Register this plug-in
//The first parameter is the name of the hook
//The second parameter is the reference to pluginManager
//The third It is the method executed by the plug-in
$pluginManager->register('demo', $this, 'say_hello');
}

function say_hello()
{
echo 'Hello World';
}
}
?>

$pluginManager->trigger( 'demo','');