I'm implementing hook_theme() in a custom module.

function monitor_chart_theme() {
  return array(
    'chart_monitor' => array(
      'template' => 'monitor_chart',
      'variables' => array(
        'container' => null,
        'theme' => null,
        'classes' => null,
        'chart' => null,

On the template file, I would like to add additional CSS classes the theme function gets in its parameters. I declared a preprocess function with the following code.

function monitor_chart_preprocess_chart_monitor(&$vars) {
  if ($vars['classes']) {
    foreach ($vars['classes'] as $class) {
      $vars['classes_array'][] = $class;

The template file contains the following code.

<div id="<?php print $container; ?>" class="<?php print $classes; ?>"></div>

If I don't use the preprocess function, the class attribute of <div> contains just 'chart-monitor', the name of the theme function.

Is there a more elegant way to pass extra variables to a template file?

2 Answers 2


Yes, arguments can be passed when calling the theme function:

$tpl_data = array(
    'data1' => $data1,
    'data2' => $data2,

return theme('my_theme', $tpl_data);

Then in the template $data1 and $data2 will be available.

To add a variable passed here to the default drupal class variable in the template we could add the line:

$class .= " $data1";

before the $class variable is printed.

However I think it's questionable whether or not this method is preferable to your original.

  • This is ok, but if on my tpl I cant print $data1 in "class" attribute, because "class" attribute as the default value, the name of my function (I've updated the post)
    – arrubiu
    Commented Feb 26, 2014 at 15:44
  • Sorry, I don't think I quite understand what your trying to achieve.
    – Felix Eve
    Commented Feb 26, 2014 at 15:48
  • I want to add a custom class to default one used Drupal, which is chart-monitor. The preprocess method works, but I don't know if there is a better way.
    – arrubiu
    Commented Feb 26, 2014 at 15:50
  • I've updated my answer but I not convinced it's the best way to do it. Sorry I couldn't help more...
    – Felix Eve
    Commented Feb 26, 2014 at 15:59
  • I've already try it, it doesn't work. The attribute "class" of my tpl is simply ignored :( Thanks
    – arrubiu
    Commented Feb 26, 2014 at 16:01

The only way to pass values to a template file used for a theme function is adding them to the array passed as second argument of theme(). In the case of that chart_monitor theme function, theme('chart_monitor', array('classes' => array('new_chart_class'))); would add new_chart_class to the CSS classes.

monitor_chart_preprocess_chart_monitor() doesn't need a foreach() loop.

function monitor_chart_preprocess_chart_monitor(&$vars) {
  if (is_array($vars['classes']) && !empty($vars['classes'])) {
    $vars['classes_array'] = array_merge($vars['classes_array'], $vars['classes']);

As side note, chart_monitor is the CSS class added by template_preprocess() which is called for every theme function for which preprocess functions aren't disabled.

// Initialize html class attribute for the current hook.
$variables['classes_array'] = array(

template_process() then initializes the $classes variable a template file gets.

// Flatten out classes.
$variables['classes'] = implode(' ', $variables['classes_array']);

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