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：
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');/** * 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。
注：相关教程知识阅读请移步到PHP教程频道。
