本文实例讲述了CodeIgniter框架钩子机制实现方法。分享给大家供大家参考，具体如下：

记得上一次去到喜啦面试，面试官问我一个问题：codeigniter是如何实现钩子机制的？

当时答不上来，后来回来之后查了一些资料才明白，所以在这里记录一下：

codeigniter的钩子是这样实现的：首先在框架的核心文件system/core/CodeIniter.php文件的 122行，载入Hooks类，接着在该文件中定义了几个挂载点，比如pre_system(129行)、post_controller_constructor(295行)等，并在这些挂载点上面执行hooks类的_call_hook()方法。

另附codeigniter的hooks类的源代码：

/**

* CodeIgniter

*

* An open source application development framework for PHP 5.1.6 or newer

*

* @package CodeIgniter

* @author EllisLab Dev Team

* @copyright Copyright (c) 2008 - 2014, EllisLab, Inc.

* @copyright Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)

* @license http://codeigniter.com/user_guide/license.html

* @link http://codeigniter.com

* @since Version 1.0

* @filesource

*/

// ------------------------------------------------------------------------

/**

* CodeIgniter Hooks Class

*

* Provides a mechanism to extend the base system without hacking.

*

* @package CodeIgniter

* @subpackage Libraries

* @category Libraries

* @author EllisLab Dev Team

* @link http://codeigniter.com/user_guide/libraries/encryption.html

*/

class CI_Hooks {

/**

* Determines wether hooks are enabled

*

* @var bool

*/

var $enabled = FALSE;

/**

* List of all hooks set in config/hooks.php

*

* @var array

*/

var $hooks = array();

/**

* Determines wether hook is in progress, used to prevent infinte loops

*

* @var bool

*/

var $in_progress = FALSE;

/**

* Constructor

*

*/

function __construct()

{

$this->_initialize();

log_message('debug', "Hooks Class Initialized");

}

// --------------------------------------------------------------------

/**

* Initialize the Hooks Preferences

*

* @access private

* @return void

*/

function _initialize()

{

$CFG =& load_class('Config', 'core');

// If hooks are not enabled in the config file

// there is nothing else to do

if ($CFG->item('enable_hooks') == FALSE)

{

return;

}

// Grab the "hooks" definition file.

// If there are no hooks, we're done.

if (defined('ENVIRONMENT') AND is_file(APPPATH.'config/'.ENVIRONMENT.'/hooks.php'))

{

include(APPPATH.'config/'.ENVIRONMENT.'/hooks.php');

}

elseif (is_file(APPPATH.'config/hooks.php'))

{

include(APPPATH.'config/hooks.php');

}

if ( ! isset($hook) OR ! is_array($hook))

{

return;

}

$this->hooks =& $hook;

$this->enabled = TRUE;

}

// --------------------------------------------------------------------

/**

* Call Hook

*

* Calls a particular hook

*

* @access private

* @param string the hook name

* @return mixed

*/

function _call_hook($which = '')

{

if ( ! $this->enabled OR ! isset($this->hooks[$which]))

{

return FALSE;

}

if (isset($this->hooks[$which][0]) AND is_array($this->hooks[$which][0]))

{

foreach ($this->hooks[$which] as $val)

{

$this->_run_hook($val);

}

}

else

{

$this->_run_hook($this->hooks[$which]);

}

return TRUE;

}

// --------------------------------------------------------------------

/**

* Run Hook

*

* Runs a particular hook

*

* @access private

* @param array the hook details

* @return bool

*/

function _run_hook($data)

{

if ( ! is_array($data))

{

return FALSE;

}

// -----------------------------------

// Safety - Prevents run-away loops

// -----------------------------------

// If the script being called happens to have the same

// hook call within it a loop can happen

if ($this->in_progress == TRUE)

{

return;

}

// -----------------------------------

// Set file path

// -----------------------------------

if ( ! isset($data['filepath']) OR ! isset($data['filename']))

{

return FALSE;

}

$filepath = APPPATH.$data['filepath'].'/'.$data['filename'];

if ( ! file_exists($filepath))

{

return FALSE;

}

// -----------------------------------

// Set class/function name

// -----------------------------------

$class = FALSE;

$function = FALSE;

$params = '';

if (isset($data['class']) AND $data['class'] != '')

{

$class = $data['class'];

}

if (isset($data['function']))

{

$function = $data['function'];

}

if (isset($data['params']))

{

$params = $data['params'];

}

if ($class === FALSE AND $function === FALSE)

{

return FALSE;

}

// -----------------------------------

// Set the in_progress flag

// -----------------------------------

$this->in_progress = TRUE;

// -----------------------------------

// Call the requested class and/or function

// -----------------------------------

if ($class !== FALSE)

{

if ( ! class_exists($class))

{

require($filepath);

}

$HOOK = new $class;

$HOOK->$function($params);

}

else

{

if ( ! function_exists($function))

{

require($filepath);

}

$function($params);

}

$this->in_progress = FALSE;

return TRUE;

}

}

// END CI_Hooks class

/* End of file Hooks.php */

/* Location: ./system/core/Hooks.php */

可以看出codeigniter实现钩子机制的方式不够优雅，其实完全可以使用观察者模式来实现钩子机制，将挂载点当做监听的事件。

希望本文所述对大家基于CodeIgniter框架的PHP程序设计有所帮助。