Drupal 内容分页功能实现

/**
 * Initializes a pager for theme('pager').
 *
 * This function sets up the necessary global variables so that future calls
 * to theme('pager') will render a pager that correctly corresponds to the
 * items being displayed.
 *
 * If the items being displayed result from a database query performed using
 * Drupal's database API, and if you have control over the construction of the
 * database query, you do not need to call this function directly; instead, you
 * can simply extend the query object with the 'PagerDefault' extender before
 * executing it. For example:
 * @code
 *   $query = db_select('some_table')->extend('PagerDefault');
 * @endcode
 *
 * However, if you are using a different method for generating the items to be
 * paged through, then you should call this function in preparation.
 *
 * The following example shows how this function can be used in a page callback
 * that invokes an external datastore with an SQL-like syntax:
 * @code
 *   // First find the total number of items and initialize the pager.
 *   $where = "status = 1";
 *   $total = mymodule_select("SELECT COUNT(*) FROM data " . $where)->result();
 *   $num_per_page = variable_get('mymodule_num_per_page', 10);
 *   $page = pager_default_initialize($total, $num_per_page);
 *
 *   // Next, retrieve and display the items for the current page.
 *   $offset = $num_per_page * $page;
 *   $result = mymodule_select("SELECT * FROM data " . $where . " LIMIT %d, %d", $offset, $num_per_page)->fetchAll();
 *   $output = theme('mymodule_results', array('result' => $result));
 *
 *   // Finally, display the pager controls, and return.
 *   $output .= theme('pager');
 *   return $output;
 * @endcode
 *
 * A second example involves a page callback that invokes an external search
 * service where the total number of matching results is provided as part of
 * the returned set (so that we do not need a separate query in order to obtain
 * this information). Here, we call pager_find_page() to calculate the desired
 * offset before the search is invoked:
 * @code
 *   // Perform the query, using the requested offset from pager_find_page().
 *   // This comes from a URL parameter, so here we are assuming that the URL
 *   // parameter corresponds to an actual page of results that will exist
 *   // within the set.
 *   $page = pager_find_page();
 *   $num_per_page = variable_get('mymodule_num_per_page', 10);
 *   $offset = $num_per_page * $page;
 *   $result = mymodule_remote_search($keywords, $offset, $num_per_page);
 *
 *   // Now that we have the total number of results, initialize the pager.
 *   pager_default_initialize($result->total, $num_per_page);
 *
 *   // Display the search results.
 *   $output = theme('search_results', array('results' => $result->data, 'type' => 'remote'));
 *
 *   // Finally, display the pager controls, and return.
 *   $output .= theme('pager');
 *   return $output;
 * @endcode
 *
 * @param $total
 *  The total number of items to be paged.
 * @param $limit
 *  The number of items the calling code will display per page.
 * @param $element
 *  An optional integer to distinguish between multiple pagers on one page.
 *
 * @return
 *   The number of the current page, within the pager represented by $element.
 *   This is determined from the URL query parameter $_GET['page'], or 0 by
 *   default. However, if a page that does not correspond to the actual range
 *   of the result set was requested, this function will return the closest
 *   page actually within the result set.
 */
function pager_default_initialize($total, $limit, $element = 0)