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This brief tutorial will cover altering and removing items in Drupal's menu system. See my previous blog post on hook_form_alter.

hook_menu_alter

Introduced in Drupal 6, hook_menu_alter allows you to actually alter elements in Drupal's menu system. The primary links, secondary links, tabs and page callbacks are alterable in this way. For example-- using the Content Profile module, it adds an extra tab to each user's page. If I choose the option to "Show a tab at the user's page", it will then display an extra tab when visiting that profile.

The problem with this is I find the tabs a bit unclear and want to rename them; instead of "View", "Edit" and "Profile", I want them to say "View", "Edit Account Settings", and "Edit Personal Information".

In my demo module, I'll add the following:

/**
 * Implementation of hook_menu_alter().
 */
function demo_menu_alter(&$items) {
  // Change the name of user profile tabs. 
  $items['user/%user_category/edit']['title'] = 'Edit Account Settings';
  $items['user/%user/profile/profile']['title'] = 'Edit Personal Information';
}

You can, of course, also remove menu items or tabs this way. You can find and target your specific menu item with a print_r($items) or dpm($items).

/**
 * Implementation of hook_menu_alter().
 */
function demo_menu_alter(&$items) {
  // Change the name of user profile tabs. 
  $items['user/%user/profile/profile']['title'] = 'Edit Personal Information';
  unset($items['user/%user_category/edit']['title']);
}

In Drupal 6, you can also use the Tab Tamer module.

In Drupal 6, many modules as well as custom jQuery required adding a "processed" class to elements in order for those elements to avoid being processed each time an AHAH/AJAX request is made on the page. In Drupal 7, you can now use the jQuery once() plugin instead.

Whereas in the past the jQuery may have looked like this:

$('.form-title:not(.title-processed)').addClass('title-processed').click(function() {
  // functionality here
});

It's now as easy as this:

$('.form-title').once('title').click(function() {
  // functionality here
});

Using once() will automatically apply a "title-processed" class to the element, processing it only once.

One of the first rules most people coming into the world of Drupal learn, hopefully, is to not hack core. I certainly didn't know about this when I first started out and hacked to pieces a lovely Drupal 4.6 site which, amusingly enough, still exists today. Since then, though, I've become more accustomed to the various ways of altering and overriding things in both Drupal core and contrib "the Drupal way".

Because Drupal is built modular with a strong hook API system, it gives us a lot of power in terms of changing things through our own custom modules. You can read more about creating a custom module at http://drupal.org/developing/modules -- there is also a useful module with some good examples you can download from http://drupal.org/project/examples

I'm going to go through a few different ways you can alter and override content in my next series of blog posts. This first one will cover one of the most popular.

hook_form_alter

One of the most common hooks used to override or alter things in Drupal is hook_form_alter. Drupal is driven by forms-- administration settings forms, content creation forms, contact forms, menu forms, user registration forms, etc., that I don't think I've ever worked on a Drupal site where this hook wasn't used.

Let's say, for example, you've got yourself a View with some exposed filters. By default the submit button says "Apply", but you've been asked to change that to "Submit".

My custom module is called demo. If I take a look at the link above from api.drupal.org, it tells me the parameters my function should have:

hook_form_alter(&$form, &$form_state, $form_id)

This is how it would appear in my module:

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

}

I need to find the $form_id in order to make sure I'm altering only that specific form and not the others. I usually do this just by printing out $form_id. For Views exposed filters, they all have the same $form_id which is 'views_exposed_form'. In order to make sure I'm only targetting this specific exposed form, I also use the $form['#id'] value. You can get these values by doing a print_r($form) or dpm($form) in your module. My alter now looks like this:

/**
 * Implementation of hook_form_alter().
 */
function demo_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'views_exposed_form' && $form['#id'] == 'views-exposed-form-content-search-page-1') {
    $form['submit']['#value'] = t('Search');
  }
}

I can do all sorts of things with forms here. I can remove elements, rename them, add new ones. I can also add or override submit and validation functions. Here are a few examples:

/**
 * Implementation of hook_form_alter().
 */
function demo_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'views_exposed_form' && $form['#id'] == 'views-exposed-form-content-search-page-1') {
    // Rename the submit button
    $form['submit']['#value'] = t('Search');
  }
  if ($form_id == 'search_block_form') {
    // Add default "Search" text in the searchbox
    $form['search_block_form']['#default_value'] = t('Search');
  }
  if ($form_id == 'page_node_form') {
    // Remove the "Preview" option
    unset($form['buttons']['preview']);
    // Add my extra validation function
    $form['#validate'][] = 'demo_extra_validate';
  }
}