imagine that we have a list if items in $items array that it's theme function is list_item in specific page.

code is

theme('item_list', array('items' => $items));

but in my module, I want to alter the parameter 'item_list' and I want to use my custom render function 'custom_item_list'

I know that I must register and define custom_item_list function but I don't know in what hook I am able to alter the theme_function parameter of specific element.

2 Answers 2


You can use hook_theme() function to use custom item list.

Hook theme:

function mymodule_theme($existing, $type, $theme, $path)
  if ($type == 'module')
    return array(
      'custom_item_list' => array(
        'variables' => array('var_name'=>NULL),
        'template' => 'custom-item-list',
  return array(); //will raise fatal error if void

Call it as usual:

theme('custom_item_list', array('var_name' => mymodule_variable()));
  • I agree with your idea. but as I wrote in my question, I have defined my custom theme function but I don't know in which hook I can change the theme function of specific element. for example a block that is created by another module makes list items that is rendered by item_list, now I want to alter this list and render it by my custom theme function.
    – Mehrdad201
    Apr 29, 2016 at 11:02

You need to implement hook_theme_registry_alter() which is the hook modules can use to alter a theme function implemented by other modules. hook_theme() is for theme functions your module defines itself.

Just set $theme_registry['item_list']['function'] to 'theme_custom_item_list', and theme_custom_item_list() will be called instead of theme_item_list().
Keep in mind that, if you need to alter the content of the $variables parameter passed to a theme function, and not its output, you can implement hook_preprocess_item_list(), since every theme function has its own preprocess functions.

function mymodule_preprocess_item_list(&$variables) {
  // Change the title for the list.
  $variables['title'] = 'My own list title';
  • but if I alter $theme_registry['item_list'] function , all element that are themed by item_list will be affected. I want to define a new custom theme and set the theme function of specific item, not alter the body of item_list theme function.
    – Mehrdad201
    Apr 29, 2016 at 12:47
  • If the theme function is only used by your module, then just implement hook_theme() to create a new theme function your module will call with (for example) theme('custom_item_list', $variables). if you want to use a new theme function that is used from every module on specific pages, that is a little more harder to implement.
    – apaderno
    Apr 29, 2016 at 14:34
  • i want to know, If I want to set a new theme_function wrapper for specific element, in which hook I am able to do that before the element rendering.
    – Mehrdad201
    Apr 29, 2016 at 15:42

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