How to use modules in Drupal

When you finish a series of module actions: download, install and enable; you would wonder how front-end UI accesses or uses your installed modules. From Drupal's codes, i know that there are two ways: one is through menu, the other is by block.

1. Menu Way

function blog_menu() {
  $items['blog'] = array(
    'title' => 'Blogs',
    'page callback' => 'blog_page_last',
    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
    'file' => 'blog.pages.inc',
  );
}

You can make a menu in the front page and call blog_page_last when you access it. Referring to following code, blog_page_last returns array-type data.

function blog_page_last() {
  global $user;
  $build = array();

  $query = db_select('node', 'n')->extend('PagerDefault');
  $nids = $query
    ->fields('n', array('nid', 'sticky', 'created'))
    ->condition('type', 'blog')
    ->condition('status', 1)
    ->orderBy('sticky', 'DESC')
    ->orderBy('created', 'DESC')
    ->limit(variable_get('default_nodes_main', 10))
    ->addTag('node_access')
    ->execute()
    ->fetchCol();

  if (!empty($nids)) {
    $nodes = node_load_multiple($nids);
    $build += node_view_multiple($nodes);
    $build['pager'] = array(
      '#theme' => 'pager',
      '#weight' => 5,
    );
  }
  else {
    drupal_set_message(t('No blog entries have been created.'));
  }
  drupal_add_feed('blog/feed', t('RSS - blogs'));

  return $build;
}

If callback function returns html markup data, it will show directly. If the page callback result is array-type data, it will use drupal_delivery_page method to render the content.

 $page_callback_result = call_user_func_array($router_item['page_callback'], $router_item['page_arguments']);

drupal_deliver_page($page_callback_result, $default_delivery_callback);

Let us examine drupal_deliver_page method's codes

function drupal_deliver_page($page_callback_result, $default_delivery_callback = NULL) {
  if (!isset($default_delivery_callback) && ($router_item = menu_get_item())) {
    $default_delivery_callback = $router_item['delivery_callback'];
  }
  $delivery_callback = !empty($default_delivery_callback) ? $default_delivery_callback : 'drupal_deliver_html_page';
  // Give modules a chance to alter the delivery callback used, based on
  // request-time context (e.g., HTTP request headers).
  drupal_alter('page_delivery_callback', $delivery_callback);
  if (function_exists($delivery_callback)) {
    $delivery_callback($page_callback_result);
  }
  else {
    // If a delivery callback is specified, but doesn't exist as a function,
    // something is wrong, but don't print anything, since it's not known
    // what format the response needs to be in.
    watchdog('delivery callback not found', 'callback %callback not found: %q.', array('%callback' => $delivery_callback, '%q' => $_GET['q']), WATCHDOG_ERROR);
  }
}

The default callback is drupal_deliver_html_page, but there provides two options: delivery_callback and page_delivery_callback. delivery_callback is used in the menu definition and page_delivery_callback is for alter hook.

2 Block way

You can assign the block to one region and the block content will show in the region correspondingly.

function blog_block_view($delta = '') {
  global $user;

  if (user_access('access content')) {
    $result = db_select('node', 'n')
      ->fields('n', array('nid', 'title', 'created'))
      ->condition('type', 'blog')
      ->condition('status', 1)
      ->orderBy('created', 'DESC')
      ->range(0, variable_get('blog_block_count', 10))
      ->addTag('node_access')
      ->execute();

    if ($node_title_list = node_title_list($result)) {
      $block['subject'] = t('Recent blog posts');
      $block['content']['blog_list'] = $node_title_list;
      $block['content']['blog_more'] = array(
        '#theme' => 'more_link',
        '#url' => 'blog',
        '#title' => t('Read the latest blog entries.'),
      );

      return $block;
    }
  }
}

The regions are defined in the theme info files and can be managed by admin in the structure block area. the content is rendered by theme function hook_more_link.

if (isset($elements['#theme'])) {
    $elements['#children'] = theme($elements['#theme'], $elements);
  }

  $output = $prefix . $elements['#children'] . $suffix;