CodeIgniterでバリデーション後のドロップダウンの選択値を再設定する方法

登録フォームなどがある画面で、入力値をチェックし問題がある場合は再度入力画面を表示する処理があると思います。
そのときに画面にドロップダウンがあると選択値を再設定する必要がありますが、CodeIgniter標準のform_dropdownでは値の再設定が不可能です。

対応方法としては既存機能を上書きで修正します。
環境：CodeIgniter v2.0.0

1.次の場所に「MY_form_helper.php」を作成する

/application/helpers/MY_form_helper.php

2.次のコードをMY_form_helper.phpに貼り付ける

<?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		ExpressionEngine Dev Team
 * @copyright	Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license		http://codeigniter.com/user_guide/license.html
 * @link		http://codeigniter.com
 * @since		Version 1.0
 * @filesource
 */

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

/**
 * CodeIgniter MY Form Helpers
 *
 * @package		CodeIgniter
 * @subpackage	Helpers
 * @category	Helpers
 * @author		ExpressionEngine Dev Team
 * @link		http://codeigniter.com/user_guide/helpers/form_helper.html
 */

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

/**
 * Custom Drop-down Menu
 *
 * @access	public
 * @param	string
 * @param	array
 * @param	string
 * @param	string
 * @return	string
 */
if ( ! function_exists('form_dropdown'))
{
	function form_dropdown($name = '', $options = array(), $selected = array(), $extra = '')
	{
		if (! is_array($selected))
		{
			$selected = array($selected);
		}

		# Insert the following code
		//-------------------------
		// Check post if post is not empty
		if (! empty($_POST))
    	{
    		// Post data exists. Default is select has no options selected. 
			$selected = array();
			// Strip the [] from the name if multiple
			$post_name = preg_replace('/\[\]/','',$name);
			// Check for value(s) for this select item by name in $_POST array
			if (isset($_POST[$post_name]))
			{
				// Check if multiple values
				if (is_array($_POST[$post_name]))
				{
					// Extract each posted item
					foreach ($_POST[$post_name] as $posted)
					{
						// Override default values with posted values
						$selected[] = $posted;
					}
				}
				else
				{
					// Single select value
					$selected = array($_POST[$post_name]);
				}
			}
		} 

		// If no selected state was submitted we will attempt to set it automatically
		if (count($selected) === 0)
		{
			// If the form name appears in the $_POST array we have a winner!
			if (isset($_POST[$name]))
			{
				$selected = array($_POST[$name]);
			}
		}

		if ($extra != '') $extra = ' '.$extra;

		$multiple = (count($selected) > 1 && strpos($extra, 'multiple') === FALSE) ? ' multiple="multiple"' : '';

		$form = '<select name="'.$name.'"'.$extra.$multiple.">\n";

		foreach ($options as $key => $val)
		{
			$key = (string) $key;

			if (is_array($val) && ! empty($val))
			{
				$form .= '<optgroup label="'.$key.'">'."\n";

				foreach ($val as $optgroup_key => $optgroup_val)
				{
					$sel = (in_array($optgroup_key, $selected)) ? ' selected="selected"' : '';

					$form .= '<option value="'.$optgroup_key.'"'.$sel.'>'.(string) $optgroup_val."</option>\n";
				}

				$form .= '</optgroup>'."\n";
			}
			else
			{
				$sel = (in_array($key, $selected)) ? ' selected="selected"' : '';

				$form .= '<option value="'.$key.'"'.$sel.'>'.(string) $val."</option>\n";
			}
		}

		$form .= '</select>';

		return $form;
	}
}

/* End of file MY_form_helper.php */
/* Location: ./application/helpers/MY_form_helper.php */