Walker::walk( array $elements, int $max_depth, mixed $args )

Display array of elements hierarchically.


Description Description

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.


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Parameters Parameters

$elements

(array) (Required) An array of elements.

$max_depth

(int) (Required) The maximum hierarchical depth.

$args

(mixed) (Optional) additional arguments.


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Return Return

(string) The hierarchical item output.


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More Information More Information

This method can be used to initialize the Walker class. It takes an array of elements ordered so that children occur below their parents. The $max_depth parameter is an integer that specifies how deep into the tree structure the walker should render. By default, the $max_depth argument uses 0, which will render every item in every branch, with no depth limit. You can also specify -1 to render all objects as a “flattened” single-dimensional list. Any other number will limit the depth that Walker will render in any branch. Any additional arguments passed to this method will be passed unchanged to the other methods.


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Source Source

File: wp-includes/class-wp-walker.php

	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, eg.
		 * 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;
	}


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Changelog Changelog

Changelog
Version Description
5.3.0 Formalized the existing ...$args parameter by adding it to the function signature.
2.1.0 Introduced.

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