+
+ /**
+ * paged_walk() - produce a page of nested elements
+ *
+ * Given an array of hierarchical elements, the maximum depth, a specific page number,
+ * and number of elements per page, this function first determines all top level root elements
+ * belonging to that page, then lists them and all of their children in hierarchical order.
+ *
+ * @package WordPress
+ * @since 2.7
+ * @param $max_depth = 0 means display all levels; $max_depth > 0 specifies the number of display levels.
+ * @param $page_num the specific page number, beginning with 1.
+ * @return XHTML of the specified page of elements
+ */
+ function paged_walk( $elements, $max_depth, $page_num, $per_page ) {
+
+ /* sanity check */
+ if ( empty($elements) || $max_depth < -1 )
+ return '';
+
+ $args = array_slice( func_get_args(), 4 );
+ $output = '';
+
+ $id_field = $this->db_fields['id'];
+ $parent_field = $this->db_fields['parent'];
+
+ $count = -1;
+ if ( -1 == $max_depth )
+ $total_top = count( $elements );
+ if ( $page_num < 1 || $per_page < 0 ) {
+ // No paging
+ $paging = false;
+ $start = 0;
+ if ( -1 == $max_depth )
+ $end = $total_top;
+ $this->max_pages = 1;
+ } else {
+ $paging = true;
+ $start = ( (int)$page_num - 1 ) * (int)$per_page;
+ $end = $start + $per_page;
+ if ( -1 == $max_depth )
+ $this->max_pages = ceil($total_top / $per_page);
+ }
+
+ // flat display
+ if ( -1 == $max_depth ) {
+ if ( !empty($args[0]['reverse_top_level']) ) {
+ $elements = array_reverse( $elements );
+ $oldstart = $start;
+ $start = $total_top - $end;
+ $end = $total_top - $oldstart;
+ }
+
+ $empty_array = array();
+ foreach ( $elements as $e ) {
+ $count++;
+ if ( $count < $start )
+ continue;
+ if ( $count >= $end )
+ break;
+ $this->display_element( $e, $empty_array, 1, 0, $args, $output );
+ }
+ return $output;
+ }
+
+ /*
+ * seperate elements into two buckets: top level and children elements
+ * children_elements is two dimensional array, eg.
+ * children_elements[10][] contains all sub-elements whose parent is 10.
+ */
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e) {
+ if ( 0 == $e->$parent_field )
+ $top_level_elements[] = $e;
+ else
+ $children_elements[ $e->$parent_field ][] = $e;
+ }
+
+ $total_top = count( $top_level_elements );
+ if ( $paging )
+ $this->max_pages = ceil($total_top / $per_page);
+ else
+ $end = $total_top;
+
+ if ( !empty($args[0]['reverse_top_level']) ) {
+ $top_level_elements = array_reverse( $top_level_elements );
+ $oldstart = $start;
+ $start = $total_top - $end;
+ $end = $total_top - $oldstart;
+ }
+ if ( !empty($args[0]['reverse_children']) ) {
+ foreach ( $children_elements as $parent => $children )
+ $children_elements[$parent] = array_reverse( $children );
+ }
+
+ foreach ( $top_level_elements as $e ) {
+ $count++;
+
+ //for the last page, need to unset earlier children in order to keep track of orphans
+ if ( $end >= $total_top && $count < $start )
+ $this->unset_children( $e, $children_elements );
+
+ if ( $count < $start )
+ continue;
+
+ if ( $count >= $end )
+ break;
+
+ $this->display_element( $e, $children_elements, $max_depth, 0, $args, $output );
+ }
+
+ if ( $end >= $total_top && count( $children_elements ) > 0 ) {
+ $empty_array = array();
+ foreach ( $children_elements as $orphans )
+ foreach( $orphans as $op )
+ $this->display_element( $op, $empty_array, 1, 0, $args, $output );
+ }
+
+ return $output;
+ }
+
+ function get_number_of_root_elements( $elements ){
+
+ $num = 0;
+ $parent_field = $this->db_fields['parent'];
+
+ foreach ( $elements as $e) {
+ if ( 0 == $e->$parent_field )
+ $num++;
+ }
+ return $num;
+ }
+
+ // unset all the children for a given top level element
+ function unset_children( $e, &$children_elements ){
+
+ if ( !$e || !$children_elements )
+ return;
+
+ $id_field = $this->db_fields['id'];
+ $id = $e->$id_field;
+
+ if ( !empty($children_elements[$id]) && is_array($children_elements[$id]) )
+ foreach ( (array) $children_elements[$id] as $child )
+ $this->unset_children( $child, $children_elements );
+
+ if ( isset($children_elements[$id]) )
+ unset( $children_elements[$id] );
+
+ }