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Walker_Nav_Menu

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概述

Walker_Nav_Menu 是 WordPress 核心类，用于生成导航菜单的 HTML 列表结构。它继承自 Walker 类，通过一系列方法控制菜单项的渲染过程，支持深度、类、ID 和属性过滤。

关键要点

  • 继承自 Walker 类，用于处理 post_type、taxonomy 和 custom 类型的树状结构。
  • 定义了 $tree_type 和 $db_fields 属性，指定处理类型和数据库字段映射。
  • 包含 start_lvl、end_lvl、start_el、end_el 等方法，分别控制菜单列表和元素的开始与结束输出。
  • 提供 build_atts 方法，用于从键值对数组构建 HTML 属性字符串。
  • 支持多个过滤器（如 nav_menu_submenu_css_class、nav_menu_item_args、nav_menu_css_class 等），允许开发者自定义菜单输出。
  • 自 6.8.0 版本起，构造函数中初始化隐私政策 URL，用于相关链接处理。

代码示例

// 示例：自定义 Walker_Nav_Menu 子类以修改菜单输出
class Custom_Walker_Nav_Menu extends Walker_Nav_Menu {
    public function start_el( &$output, $data_object, $depth = 0, $args = null, $current_object_id = 0 ) {
        // 自定义逻辑，例如添加额外类或属性
        parent::start_el( $output, $data_object, $depth, $args, $current_object_id );
    }
}

// 在 wp_nav_menu 中使用自定义 Walker
wp_nav_menu( array(
    'walker' => new Custom_Walker_Nav_Menu(),
) );

注意事项

  • 使用 item_spacing 参数控制 HTML 输出中的缩进和换行，'discard' 值可移除空白。
  • 过滤器如 nav_menu_item_title 和 nav_menu_link_attributes 允许灵活调整菜单项标题和链接属性。
  • 自 6.7.0 版本起，移除了冗余的 title 属性，仅在 attr_title 与标题不同时添加。
  • 类方法中的参数命名在 5.9.0 和 6.7.0 版本有更新，以支持 PHP 8 命名参数，需注意向后兼容性。
📄 原文内容

Core class used to implement an HTML list of nav menu items.

Description

See also

Methods

Name Description
Walker_Nav_Menu::__construct Constructor.
Walker_Nav_Menu::build_atts Builds a string of HTML attributes from an array of key/value pairs.
Walker_Nav_Menu::end_el Ends the element output, if needed.
Walker_Nav_Menu::end_lvl Ends the list of after the elements are added.
Walker_Nav_Menu::start_el Starts the element output.
Walker_Nav_Menu::start_lvl Starts the list before the elements are added.

Source

class Walker_Nav_Menu extends Walker {
	/**
	 * What the class handles.
	 *
	 * @since 3.0.0
	 * @var string
	 *
	 * @see Walker::$tree_type
	 */
	public $tree_type = array( 'post_type', 'taxonomy', 'custom' );

	/**
	 * Database fields to use.
	 *
	 * @since 3.0.0
	 * @todo Decouple this.
	 * @var string[]
	 *
	 * @see Walker::$db_fields
	 */
	public $db_fields = array(
		'parent' => 'menu_item_parent',
		'id'     => 'db_id',
	);

	/**
	 * The URL to the privacy policy page.
	 *
	 * @since 6.8.0
	 * @var string
	 */
	private $privacy_policy_url;

	/**
	 * Constructor.
	 *
	 * @since 6.8.0
	 */
	public function __construct() {
		$this->privacy_policy_url = get_privacy_policy_url();
	}

	/**
	 * Starts the list before the elements are added.
	 *
	 * @since 3.0.0
	 *
	 * @see Walker::start_lvl()
	 *
	 * @param string   $output Used to append additional content (passed by reference).
	 * @param int      $depth  Depth of menu item. Used for padding.
	 * @param stdClass $args   An object of wp_nav_menu() arguments.
	 */
	public function start_lvl( &$output, $depth = 0, $args = null ) {
		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
			$t = '';
			$n = '';
		} else {
			$t = "t";
			$n = "n";
		}
		$indent = str_repeat( $t, $depth );

		// Default class.
		$classes = array( 'sub-menu' );

		/**
		 * Filters the CSS class(es) applied to a menu list element.
		 *
		 * @since 4.8.0
		 *
		 * @param string[] $classes Array of the CSS classes that are applied to the menu `<ul>` element.
		 * @param stdClass $args    An object of `wp_nav_menu()` arguments.
		 * @param int      $depth   Depth of menu item. Used for padding.
		 */
		$class_names = implode( ' ', apply_filters( 'nav_menu_submenu_css_class', $classes, $args, $depth ) );

		$atts          = array();
		$atts['class'] = ! empty( $class_names ) ? $class_names : '';

		/**
		 * Filters the HTML attributes applied to a menu list element.
		 *
		 * @since 6.3.0
		 *
		 * @param array $atts {
		 *     The HTML attributes applied to the `<ul>` element, empty strings are ignored.
		 *
		 *     @type string $class    HTML CSS class attribute.
		 * }
		 * @param stdClass $args      An object of `wp_nav_menu()` arguments.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$atts       = apply_filters( 'nav_menu_submenu_attributes', $atts, $args, $depth );
		$attributes = $this->build_atts( $atts );

		$output .= "{$n}{$indent}<ul{$attributes}>{$n}";
	}

	/**
	 * Ends the list of after the elements are added.
	 *
	 * @since 3.0.0
	 *
	 * @see Walker::end_lvl()
	 *
	 * @param string   $output Used to append additional content (passed by reference).
	 * @param int      $depth  Depth of menu item. Used for padding.
	 * @param stdClass $args   An object of wp_nav_menu() arguments.
	 */
	public function end_lvl( &$output, $depth = 0, $args = null ) {
		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
			$t = '';
			$n = '';
		} else {
			$t = "t";
			$n = "n";
		}
		$indent  = str_repeat( $t, $depth );
		$output .= "$indent</ul>{$n}";
	}

	/**
	 * Starts the element output.
	 *
	 * @since 3.0.0
	 * @since 4.4.0 The 'nav_menu_item_args' filter was added.
	 * @since 5.9.0 Renamed `$item` to `$data_object` and `$id` to `$current_object_id`
	 *              to match parent class for PHP 8 named parameter support.
	 * @since 6.7.0 Removed redundant title attributes.
	 *
	 * @see Walker::start_el()
	 *
	 * @param string   $output            Used to append additional content (passed by reference).
	 * @param WP_Post  $data_object       Menu item data object.
	 * @param int      $depth             Depth of menu item. Used for padding.
	 * @param stdClass $args              An object of wp_nav_menu() arguments.
	 * @param int      $current_object_id Optional. ID of the current menu item. Default 0.
	 */
	public function start_el( &$output, $data_object, $depth = 0, $args = null, $current_object_id = 0 ) {
		// Restores the more descriptive, specific name for use within this method.
		$menu_item = $data_object;

		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
			$t = '';
			$n = '';
		} else {
			$t = "t";
			$n = "n";
		}
		$indent = ( $depth ) ? str_repeat( $t, $depth ) : '';

		$classes   = empty( $menu_item->classes ) ? array() : (array) $menu_item->classes;
		$classes[] = 'menu-item-' . $menu_item->ID;

		/**
		 * Filters the arguments for a single nav menu item.
		 *
		 * @since 4.4.0
		 *
		 * @param stdClass $args      An object of wp_nav_menu() arguments.
		 * @param WP_Post  $menu_item Menu item data object.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$args = apply_filters( 'nav_menu_item_args', $args, $menu_item, $depth );

		/**
		 * Filters the CSS classes applied to a menu item's list item element.
		 *
		 * @since 3.0.0
		 * @since 4.1.0 The `$depth` parameter was added.
		 *
		 * @param string[] $classes   Array of the CSS classes that are applied to the menu item's `<li>` element.
		 * @param WP_Post  $menu_item The current menu item object.
		 * @param stdClass $args      An object of wp_nav_menu() arguments.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$class_names = implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $menu_item, $args, $depth ) );

		/**
		 * Filters the ID attribute applied to a menu item's list item element.
		 *
		 * @since 3.0.1
		 * @since 4.1.0 The `$depth` parameter was added.
		 *
		 * @param string   $menu_item_id The ID attribute applied to the menu item's `<li>` element.
		 * @param WP_Post  $menu_item    The current menu item.
		 * @param stdClass $args         An object of wp_nav_menu() arguments.
		 * @param int      $depth        Depth of menu item. Used for padding.
		 */
		$id = apply_filters( 'nav_menu_item_id', 'menu-item-' . $menu_item->ID, $menu_item, $args, $depth );

		$li_atts          = array();
		$li_atts['id']    = ! empty( $id ) ? $id : '';
		$li_atts['class'] = ! empty( $class_names ) ? $class_names : '';

		/**
		 * Filters the HTML attributes applied to a menu's list item element.
		 *
		 * @since 6.3.0
		 *
		 * @param array $li_atts {
		 *     The HTML attributes applied to the menu item's `<li>` element, empty strings are ignored.
		 *
		 *     @type string $class        HTML CSS class attribute.
		 *     @type string $id           HTML id attribute.
		 * }
		 * @param WP_Post  $menu_item The current menu item object.
		 * @param stdClass $args      An object of wp_nav_menu() arguments.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$li_atts       = apply_filters( 'nav_menu_item_attributes', $li_atts, $menu_item, $args, $depth );
		$li_attributes = $this->build_atts( $li_atts );

		$output .= $indent . '<li' . $li_attributes . '>';

		/** This filter is documented in wp-includes/post-template.php */
		$title = apply_filters( 'the_title', $menu_item->title, $menu_item->ID );

		// Save filtered value before filtering again.
		$the_title_filtered = $title;

		/**
		 * Filters a menu item's title.
		 *
		 * @since 4.4.0
		 *
		 * @param string   $title     The menu item's title.
		 * @param WP_Post  $menu_item The current menu item object.
		 * @param stdClass $args      An object of wp_nav_menu() arguments.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$title = apply_filters( 'nav_menu_item_title', $title, $menu_item, $args, $depth );

		$atts           = array();
		$atts['target'] = ! empty( $menu_item->target ) ? $menu_item->target : '';
		$atts['rel']    = ! empty( $menu_item->xfn ) ? $menu_item->xfn : '';

		if ( ! empty( $menu_item->url ) ) {
			if ( $this->privacy_policy_url === $menu_item->url ) {
				$atts['rel'] = empty( $atts['rel'] ) ? 'privacy-policy' : $atts['rel'] . ' privacy-policy';
			}

			$atts['href'] = $menu_item->url;
		} else {
			$atts['href'] = '';
		}

		$atts['aria-current'] = $menu_item->current ? 'page' : '';

		// Add title attribute only if it does not match the link text (before or after filtering).
		if ( ! empty( $menu_item->attr_title )
			&& trim( strtolower( $menu_item->attr_title ) ) !== trim( strtolower( $menu_item->title ) )
			&& trim( strtolower( $menu_item->attr_title ) ) !== trim( strtolower( $the_title_filtered ) )
			&& trim( strtolower( $menu_item->attr_title ) ) !== trim( strtolower( $title ) )
		) {
			$atts['title'] = $menu_item->attr_title;
		} else {
			$atts['title'] = '';
		}

		/**
		 * Filters the HTML attributes applied to a menu item's anchor element.
		 *
		 * @since 3.6.0
		 * @since 4.1.0 The `$depth` parameter was added.
		 *
		 * @param array $atts {
		 *     The HTML attributes applied to the menu item's `<a>` element, empty strings are ignored.
		 *
		 *     @type string $title        Title attribute.
		 *     @type string $target       Target attribute.
		 *     @type string $rel          The rel attribute.
		 *     @type string $href         The href attribute.
		 *     @type string $aria-current The aria-current attribute.
		 * }
		 * @param WP_Post  $menu_item The current menu item object.
		 * @param stdClass $args      An object of wp_nav_menu() arguments.
		 * @param int      $depth     Depth of menu item. Used for padding.
		 */
		$atts       = apply_filters( 'nav_menu_link_attributes', $atts, $menu_item, $args, $depth );
		$attributes = $this->build_atts( $atts );

		$item_output  = $args->before;
		$item_output .= '<a' . $attributes . '>';
		$item_output .= $args->link_before . $title . $args->link_after;
		$item_output .= '</a>';
		$item_output .= $args->after;

		/**
		 * Filters a menu item's starting output.
		 *
		 * The menu item's starting output only includes `$args->before`, the opening `<a>`,
		 * the menu item's title, the closing `</a>`, and `$args->after`. Currently, there is
		 * no filter for modifying the opening and closing `<li>` for a menu item.
		 *
		 * @since 3.0.0
		 *
		 * @param string   $item_output The menu item's starting HTML output.
		 * @param WP_Post  $menu_item   Menu item data object.
		 * @param int      $depth       Depth of menu item. Used for padding.
		 * @param stdClass $args        An object of wp_nav_menu() arguments.
		 */
		$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $menu_item, $depth, $args );
	}

	/**
	 * Ends the element output, if needed.
	 *
	 * @since 3.0.0
	 * @since 5.9.0 Renamed `$item` to `$data_object` to match parent class for PHP 8 named parameter support.
	 *
	 * @see Walker::end_el()
	 *
	 * @param string   $output      Used to append additional content (passed by reference).
	 * @param WP_Post  $data_object Menu item data object. Not used.
	 * @param int      $depth       Depth of page. Not Used.
	 * @param stdClass $args        An object of wp_nav_menu() arguments.
	 */
	public function end_el( &$output, $data_object, $depth = 0, $args = null ) {
		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
			$t = '';
			$n = '';
		} else {
			$t = "t";
			$n = "n";
		}
		$output .= "</li>{$n}";
	}

	/**
	 * Builds a string of HTML attributes from an array of key/value pairs.
	 * Empty values are ignored.
	 *
	 * @since 6.3.0
	 *
	 * @param  array $atts Optional. An array of HTML attribute key/value pairs. Default empty array.
	 * @return string A string of HTML attributes.
	 */
	protected function build_atts( $atts = array() ) {
		$attribute_string = '';
		foreach ( $atts as $attr => $value ) {
			if ( false !== $value && '' !== $value && is_scalar( $value ) ) {
				$value             = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
				$attribute_string .= ' ' . $attr . '="' . $value . '"';
			}
		}
		return $attribute_string;
	}
}

View all references View on Trac View on GitHub

Uses Description
Walkerwp-includes/class-wp-walker.php

A class for displaying various tree-like structures.
Used by Description
Walker_Nav_Menu_Editwp-admin/includes/class-walker-nav-menu-edit.php

Create HTML list of nav menu input items.
Walker_Nav_Menu_Checklistwp-admin/includes/class-walker-nav-menu-checklist.php

Create HTML list of nav menu input items.

Changelog

Version Description
3.0.0 Introduced.