/** * A class for displaying various tree-like structures. * * Extend the Walker class to use it, see examples below. Child classes * do not need to implement all of the abstract methods in the class. The child * only needs to implement the methods that are needed. * * @since 2.1.0 * * @package WordPress * @abstract */ class Walker { /** * What the class handles. * * @since 2.1.0 * @var string */ public $tree_type; /** * DB fields to use. * * @since 2.1.0 * @var array */ public $db_fields; /** * Max number of pages walked by the paged walker * * @since 2.7.0 * @var int */ public $max_pages = 1; /** * Whether the current element has children or not. * * To be used in start_el(). * * @since 4.0.0 * @var bool */ public $has_children; /** * Starts the list before the elements are added. * * The $args parameter holds additional values that may be used with the child * class methods. This method is called at the start of the output list. * * @since 2.1.0 * @abstract * * @param string $output Used to append additional content (passed by reference). * @param int $depth Depth of the item. * @param array $args An array of additional arguments. */ public function start_lvl( &$output, $depth = 0, $args = array() ) {} /** * Ends the list of after the elements are added. * * The $args parameter holds additional values that may be used with the child * class methods. This method finishes the list at the end of output of the elements. * * @since 2.1.0 * @abstract * * @param string $output Used to append additional content (passed by reference). * @param int $depth Depth of the item. * @param array $args An array of additional arguments. */ public function end_lvl( &$output, $depth = 0, $args = array() ) {} /** * Start the element output. * * The $args parameter holds additional values that may be used with the child * class methods. Includes the element output also. * * @since 2.1.0 * @since 5.9.0 Renamed `$object` (a PHP reserved keyword) to `$data_object` for PHP 8 named parameter support. * @abstract * * @param string $output Used to append additional content (passed by reference). * @param object $data_object The data object. * @param int $depth Depth of the item. * @param array $args An array of additional arguments. * @param int $current_object_id Optional. ID of the current item. Default 0. */ public function start_el( &$output, $data_object, $depth = 0, $args = array(), $current_object_id = 0 ) {} /** * Ends the element output, if needed. * * The $args parameter holds additional values that may be used with the child class methods. * * @since 2.1.0 * @since 5.9.0 Renamed `$object` (a PHP reserved keyword) to `$data_object` for PHP 8 named parameter support. * @abstract * * @param string $output Used to append additional content (passed by reference). * @param object $data_object The data object. * @param int $depth Depth of the item. * @param array $args An array of additional arguments. */ public function end_el( &$output, $data_object, $depth = 0, $args = array() ) {} /** * Traverse elements to create list from elements. * * Display one element if the element doesn't have any children otherwise, * display the element and its children. Will only traverse up to the max * depth and no ignore elements under that depth. It is possible to set the * max depth to include all depths, see walk() method. * * This method should not be called directly, use the walk() method instead. * * @since 2.5.0 * * @param object $element Data object. * @param array $children_elements List of elements to continue traversing (passed by reference). * @param int $max_depth Max depth to traverse. * @param int $depth Depth of current element. * @param array $args An array of arguments. * @param string $output Used to append additional content (passed by reference). */ public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) { if ( ! $element ) { return; } $id_field = $this->db_fields['id']; $id = $element->$id_field; // Display this element. $this->has_children = ! empty( $children_elements[ $id ] ); if ( isset( $args[0] ) && is_array( $args[0] ) ) { $args[0]['has_children'] = $this->has_children; // Back-compat. } $this->start_el( $output, $element, $depth, ...array_values( $args ) ); // Descend only when the depth is right and there are children for this element. if ( ( 0 == $max_depth || $max_depth > $depth + 1 ) && isset( $children_elements[ $id ] ) ) { foreach ( $children_elements[ $id ] as $child ) { if ( ! isset( $newlevel ) ) { $newlevel = true; // Start the child delimiter. $this->start_lvl( $output, $depth, ...array_values( $args ) ); } $this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output ); } unset( $children_elements[ $id ] ); } if ( isset( $newlevel ) && $newlevel ) { // End the child delimiter. $this->end_lvl( $output, $depth, ...array_values( $args ) ); } // End this element. $this->end_el( $output, $element, $depth, ...array_values( $args ) ); } /** * Display array of elements hierarchically. * * Does not assume any existing order of elements. * * $max_depth = -1 means flatly display every element. * $max_depth = 0 means display all levels. * $max_depth > 0 specifies the number of display levels. * * @since 2.1.0 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it * to the function signature. * * @param array $elements An array of elements. * @param int $max_depth The maximum hierarchical depth. * @param mixed ...$args Optional additional arguments. * @return string The hierarchical item output. */ public function walk( $elements, $max_depth, ...$args ) { $output = ''; // Invalid parameter or nothing to walk. if ( $max_depth < -1 || empty( $elements ) ) { return $output; } $parent_field = $this->db_fields['parent']; // Flat display. if ( -1 == $max_depth ) { $empty_array = array(); foreach ( $elements as $e ) { $this->display_element( $e, $empty_array, 1, 0, $args, $output ); } return $output; } /* * Need to display in hierarchical order. * Separate elements into two buckets: top level and children elements. * Children_elements is two dimensional array. Example: * Children_elements[10][] contains all sub-elements whose parent is 10. */ $top_level_elements = array(); $children_elements = array(); foreach ( $elements as $e ) { if ( empty( $e->$parent_field ) ) { $top_level_elements[] = $e; } else { $children_elements[ $e->$parent_field ][] = $e; } } /* * When none of the elements is top level. * Assume the first one must be root of the sub elements. */ if ( empty( $top_level_elements ) ) { $first = array_slice( $elements, 0, 1 ); $root = $first[0]; $top_level_elements = array(); $children_elements = array(); foreach ( $elements as $e ) { if ( $root->$parent_field == $e->$parent_field ) { $top_level_elements[] = $e; } else { $children_elements[ $e->$parent_field ][] = $e; } } } foreach ( $top_level_elements as $e ) { $this->display_element( $e, $children_elements, $max_depth, 0, $args, $output ); } /* * If we are displaying all levels, and remaining children_elements is not empty, * then we got orphans, which should be displayed regardless. */ if ( ( 0 == $max_depth ) && 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; } /** * 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. * * $max_depth = 0 means display all levels. * $max_depth > 0 specifies the number of display levels. * * @since 2.7.0 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it * to the function signature. * * @param array $elements * @param int $max_depth The maximum hierarchical depth. * @param int $page_num The specific page number, beginning with 1. * @param int $per_page * @param mixed ...$args Optional additional arguments. * @return string XHTML of the specified page of elements */ public function paged_walk( $elements, $max_depth, $page_num, $per_page, ...$args ) { if ( empty( $elements ) || $max_depth < -1 ) { return ''; } $output = ''; $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; } /* * Separate elements into two buckets: top level and children elements. * Children_elements is two dimensional array, e.g. * $children_elements[10][] contains all sub-elements whose parent is 10. */ $top_level_elements = array(); $children_elements = array(); foreach ( $elements as $e ) { if ( empty( $e->$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; } /** * Calculates the total number of root elements. * * @since 2.7.0 * * @param array $elements Elements to list. * @return int Number of root elements. */ public function get_number_of_root_elements( $elements ) { $num = 0; $parent_field = $this->db_fields['parent']; foreach ( $elements as $e ) { if ( empty( $e->$parent_field ) ) { $num++; } } return $num; } /** * Unset all the children for a given top level element. * * @since 2.7.0 * * @param object $e * @param array $children_elements */ public 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 ); } } unset( $children_elements[ $id ] ); } }