"cannot use a scalar value as an array" warning for adding #prefix and #suffix in template.php via hook-form-alter – Drupal 7

Question

I have the following code in my Drupal’s template.php file. What it does is to embed every element of my site's contact form (created with the Webform module) in a li element (the form itself is already embedded in a ul element).

function MYTHEME_form_alter(&$form, &$form_state, $form_id) {

  if ($form_id == 'webform_client_form_MYFORMID') {
    foreach($form['submitted'] as &$field) {
      $field['#prefix'] = '<li>';
      $field['#suffix'] = '</li>';
    }
  }

This works, but I get 'Warning: Cannot use a scalar value as an array in MYTHEME_form_alter()' when accessing a page that contains such a form. The warning shows twice, once for each of the two lines where I add the prefix and suffix, respectively.

I have searched far and wide, but I do not know what to do. To the best of my knowledge, this is how Drupal wants me to handle this. And like I said, it does work, but it would be nice to get rid of the warnings and do everything 100 % correct.

(I'm using Drupal 7 and PHP 5.6.24.)

Does anybody know a better / the correct way to do this? Thank you.

Answer 1

Not everything in a render array is an element to be rendered. The field contains other data in the form of properties, and some of those values will be scalar types, which causes the errors you see.

To fix, use element_children:

foreach (element_children($form['submitted']) as $key) {
  $form['submitted'][$key]['#prefix'] = '<li>';
  $form['submitted'][$key]['#suffix'] = '</li>';
}

Answer 2

if you change it to

 foreach($form['submitted'] as $key => $field) {
  $form['submitted'][$key]['#prefix'] = '<li>';
  $form['submitted'][$key]['#suffix'] = '</li>';
}

i think that will solve your problem

Answer 3

Warning: Cannot use a scalar value as an array in MYTHEME_form_alter()

It is a common PHP error which means you are treating a scalar value (eg: int, string) as an array.

You can fix it by checking if it is an array before using it.

function MYTHEME_form_alter(&$form, &$form_state, $form_id) {

  if ($form_id == 'webform_client_form_MYFORMID') {
    foreach($form['submitted'] as &$field) {
      if (is_array($field)) {
        $field['#prefix'] = '<li>';
        $field['#suffix'] = '</li>';
      }
    }
  }

As mentioned by @Clive

Since you are adding #prefix and #suffix, you are obviously trying to change for the render element. So it would be better to limit the change occurred on render element only.

element_children is the API provided by Drupal for that purpose.

function MYTHEME_form_alter(&$form, &$form_state, $form_id) {

  if ($form_id == 'webform_client_form_MYFORMID') {
    foreach($element_children($form['submitted']) as $key) {
      $field = &$form['submitted'][$key];
      $field['#prefix'] = '<li>';
      $field['#suffix'] = '</li>';
    }
  }