CodeIgniter框架钩子机制实现方法【hooks类】

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。