Drupal 7 Drupal 7.14：预处理搜索块表单为我提供了一个空白表单，以$search\u形式呈现

我从零开始处理一个主题，我尝试替换文本字段的标题，但将搜索变量内插到搜索表单中时，结果为空。有什么我可能遗漏的错误吗

`function mytheme_preprocess_search_block_form(&$form) { 
  $form['search'] = array();
  $hidden = array();
// Provide variables named after form keys so themers can print each element independently.
  foreach (element_children($form['form']) as $key) {
     echo $key;
     $type = $form['form'][$key]['#type'];
     echo '__'.$type.'<br />';
     if ($type == 'hidden' || $type == 'token') {
        $hidden[] = drupal_render($form['form'][$key]);
    }
    else {
        if($key == 'search_block_form')
        {
            $form['form'][$key]['#title'] = t('');
            //$form['search'][$key] = drupal_render($form['form'][$key]);
        }
        else
        {
        $form['search'][$key] = drupal_render($form['form'][$key]);
        }
    }
}
// Hidden form elements have no value to themers. No need for separation.
$form['search']['hidden'] = implode($hidden);
// Collect all form elements to make it easier to print the whole form.
$form['search_form'] = implode($form['search']);
 var_dump($form);
 exit;
}`

参考：

article-node-form.tpl.php

<?php echo drupal_render_children($form)?>

<?php echo drupal_render_children($form)?>