Theming forms : what am I doing wrong?

Question

I've got a simple form which I would like to run through a theme function of mine. What I do is that I've got a form builder function where I define the form. I've then used hook_theme() to define which theme function Drupal should use to theme the form.

function mymodule_theme($existing, $type, $theme, $path) {
  return array(
    'mymodule_form' => array(
      'render element' => 'form',
    ),
  );
}

Drupal does invoke the theme function. However, I've got a call to drupal_render($variables['form']) to actually render the form in my theme function. What happens then is that Drupal seems to go into a loop as this call results in mymodule_theme to be called again (and again, and again...).

function theme_mymodule_form($variables){

  // Add custom text on top.
  $output = '<span>' . t('Table description goes here') . '</span>';
  $output .= drupal_render($variables['form']);

  // Return output.
  return $output;

}

When I do a dump of $variables passed to my theme function, I see that #theme is set to 'mymodule_theme'. Should I at this point change it to 'form', and not 'mymodule_form' as I'd just like to render the form as a plain form? How should I really render the $variables'[form'] in my theme function to make it appear as a plain old form? Should I rather use theme('form', $variables['form']) for that?

As far as I understand, drupal_render($variables['form']) takes care of rendering the form and all its children, as opposed to to theme('form', $variables['form']) which only renders the immediate form and not children.

I'd be really happy if someone have the time to enlighten me on this :-)

Answer 1

In Drupal 7 you need to use drupal_render_children() instead of drupal_render() for the $form. Otherwise, if the form has the #theme property set you will get an infinite loop (as your theme function will invoke the form builder to run your theme function again, and the cycle will continue).