CodeIgniter框架钩子机制实现方法【hooks类】

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。