目录
之前提到的 register_nav_menus() 函数用于注册一个自定义菜单，而今天提到的 wp_nav_menu() 则是用来获取并显示我们的自定义菜单的。
该函数的语法为：
wp_nav_menu( array $args = array() )$args：数组（选填）。你要获取并显示的一个自定义菜单，包含各类参数。
- menu：整型、字符串或者WP项目。希望调取的菜单，可以是一个 ID 、slug 、菜单名或者对象，优先于 theme_location。
- menu_class：字符串。应用于菜单 ul 标签的 CSS 类元素。默认为“menu”。
- menu_id：字符串。应用于菜单 ul 标签的 ID 属性。默认为菜单的 slug 。
- container：字符串。包裹在 ul 标签外部的 HTML 标签。默认为 div 。
- container_class：字符串。包裹在 ul标签外部 的 HTML 标签的 CSS 类元素。默认为“menu-{menu slug}-container”。
- container_id：字符串。包裹在 ul标签外部 的 HTML 标签的 ID 属性。
- fallback_cb：回调函数或布尔值。无回调函数时可设置为 false 。默认为 wp_page_menu 。
- before：字符串。标签前的文本内容。
- after：字符串。标签后的文本内容。
- link_before：字符串，链接文本前的文本内容。
- link_after：字符串，链接文本后的文本内容。
- echo：布尔值。是否输出菜单并返回。默认为 true 。
- depth：整型。显示几级菜单。 0 代表全部显示。默认是 0 。
- walker：对象。自定义walker类的实例。
- theme_location：字符串。显示指定菜单位置的导航。 即 register_nav_menu() 中注册时使用的 key 值，后台指定该位置使用哪个菜单，WordPress 将会自动调用对应的菜单显示，比 menu 定义更方便，优先级小于 menu。
- items_wrap：字符串。如何包装列表项。 默认值是带有id和class的ul。 使用带编号占位符的 printf() 格式。
- item_spacing：字符串。是否在菜单的HTML中保留空格。 接受’保留’或’丢弃’。 默认’保留’。
该函数定义在 wp-includes/nav-menu-template.php 文件中，具体代码如下：
function wp_nav_menu( $args = array() ) {
static $menu_id_slugs = array();
$defaults = array(
\'menu\' => \'\',
\'container\' => \'div\',
\'container_class\' => \'\',
\'container_id\' => \'\',
\'menu_class\' => \'menu\',
\'menu_id\' => \'\',
\'echo\' => true,
\'fallback_cb\' => \'wp_page_menu\',
\'before\' => \'\',
\'after\' => \'\',
\'link_before\' => \'\',
\'link_after\' => \'\',
\'items_wrap\' => \'<ul id=\"%1$s\" class=\"%2$s\">%3$s</ul>\',
\'item_spacing\' => \'preserve\',
\'depth\' => 0,
\'walker\' => \'\',
\'theme_location\' => \'\',
);
$args = wp_parse_args( $args, $defaults );
if ( ! in_array( $args[\'item_spacing\'], array( \'preserve\', \'discard\' ), true ) ) {
// invalid value, fall back to default.
$args[\'item_spacing\'] = $defaults[\'item_spacing\'];
}
/**
* Filters the arguments used to display a navigation menu.
*
* @since 3.0.0
*
* @see wp_nav_menu()
*
* @param array $args Array of wp_nav_menu() arguments.
*/
$args = apply_filters( \'wp_nav_menu_args\', $args );
$args = (object) $args;
/**
* Filters whether to short-circuit the wp_nav_menu() output.
*
* Returning a non-null value to the filter will short-circuit
* wp_nav_menu(), echoing that value if $args->echo is true,
* returning that value otherwise.
*
* @since 3.9.0
*
* @see wp_nav_menu()
*
* @param string|null $output Nav menu output to short-circuit with. Default null.
* @param stdClass $args An object containing wp_nav_menu() arguments.
*/
$nav_menu = apply_filters( \'pre_wp_nav_menu\', null, $args );
if ( null !== $nav_menu ) {
if ( $args->echo ) {
echo $nav_menu;
return;
}
return $nav_menu;
}
// Get the nav menu based on the requested menu
$menu = wp_get_nav_menu_object( $args->menu );
// Get the nav menu based on the theme_location
if ( ! $menu && $args->theme_location && ( $locations = get_nav_menu_locations() ) && isset( $locations[ $args->theme_location ] ) ) {
$menu = wp_get_nav_menu_object( $locations[ $args->theme_location ] );
}
// get the first menu that has items if we still can\'t find a menu
if ( ! $menu && ! $args->theme_location ) {
$menus = wp_get_nav_menus();
foreach ( $menus as $menu_maybe ) {
if ( $menu_items = wp_get_nav_menu_items( $menu_maybe->term_id, array( \'update_post_term_cache\' => false ) ) ) {
$menu = $menu_maybe;
break;
}
}
}
if ( empty( $args->menu ) ) {
$args->menu = $menu;
}
// If the menu exists, get its items.
if ( $menu && ! is_wp_error( $menu ) && ! isset( $menu_items ) ) {
$menu_items = wp_get_nav_menu_items( $menu->term_id, array( \'update_post_term_cache\' => false ) );
}
/*
* If no menu was found:
* - Fall back (if one was specified), or bail.
*
* If no menu items were found:
* - Fall back, but only if no theme location was specified.
* - Otherwise, bail.
*/
if ( ( ! $menu || is_wp_error( $menu ) || ( isset( $menu_items ) && empty( $menu_items ) && ! $args->theme_location ) )
&& isset( $args->fallback_cb ) && $args->fallback_cb && is_callable( $args->fallback_cb ) ) {
return call_user_func( $args->fallback_cb, (array) $args );
}
if ( ! $menu || is_wp_error( $menu ) ) {
return false;
}
$nav_menu = $items = \'\';
$show_container = false;
if ( $args->container ) {
/**
* Filters the list of HTML tags that are valid for use as menu containers.
*
* @since 3.0.0
*
* @param array $tags The acceptable HTML tags for use as menu containers.
* Default is array containing \'div\' and \'nav\'.
*/
$allowed_tags = apply_filters( \'wp_nav_menu_container_allowedtags\', array( \'div\', \'nav\' ) );
if ( is_string( $args->container ) && in_array( $args->container, $allowed_tags ) ) {
$show_container = true;
$class = $args->container_class ? \' class=\"\' . esc_attr( $args->container_class ) . \'\"\' : \' class=\"menu-\' . $menu->slug . \'-container\"\';
$id = $args->container_id ? \' id=\"\' . esc_attr( $args->container_id ) . \'\"\' : \'\';
$nav_menu .= \'<\' . $args->container . $id . $class . \'>\';
}
}
// Set up the $menu_item variables
_wp_menu_item_classes_by_context( $menu_items );
$sorted_menu_items = $menu_items_with_children = array();
foreach ( (array) $menu_items as $menu_item ) {
$sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
if ( $menu_item->menu_item_parent ) {
$menu_items_with_children[ $menu_item->menu_item_parent ] = true;
}
}
// Add the menu-item-has-children class where applicable
if ( $menu_items_with_children ) {
foreach ( $sorted_menu_items as &$menu_item ) {
if ( isset( $menu_items_with_children[ $menu_item->ID ] ) ) {
$menu_item->classes[] = \'menu-item-has-children\';
}
}
}
unset( $menu_items, $menu_item );
/**
* Filters the sorted list of menu item objects before generating the menu\'s HTML.
*
* @since 3.1.0
*
* @param array $sorted_menu_items The menu items, sorted by each menu item\'s menu order.
* @param stdClass $args An object containing wp_nav_menu() arguments.
*/
$sorted_menu_items = apply_filters( \'wp_nav_menu_objects\', $sorted_menu_items, $args );
$items .= walk_nav_menu_tree( $sorted_menu_items, $args->depth, $args );
unset( $sorted_menu_items );
// Attributes
if ( ! empty( $args->menu_id ) ) {
$wrap_id = $args->menu_id;
} else {
$wrap_id = \'menu-\' . $menu->slug;
while ( in_array( $wrap_id, $menu_id_slugs ) ) {
if ( preg_match( \'#-(\\d+)$#\', $wrap_id, $matches ) ) {
$wrap_id = preg_replace( \'#-(\\d+)$#\', \'-\' . ++$matches[1], $wrap_id );
} else {
$wrap_id = $wrap_id . \'-1\';
}
}
}
$menu_id_slugs[] = $wrap_id;
$wrap_class = $args->menu_class ? $args->menu_class : \'\';
/**
* Filters the HTML list content for navigation menus.
*
* @since 3.0.0
*
* @see wp_nav_menu()
*
* @param string $items The HTML list content for the menu items.
* @param stdClass $args An object containing wp_nav_menu() arguments.
*/
$items = apply_filters( \'wp_nav_menu_items\', $items, $args );
/**
* Filters the HTML list content for a specific navigation menu.
*
* @since 3.0.0
*
* @see wp_nav_menu()
*
* @param string $items The HTML list content for the menu items.
* @param stdClass $args An object containing wp_nav_menu() arguments.
*/
$items = apply_filters( \"wp_nav_menu_{$menu->slug}_items\", $items, $args );
// Don\'t print any markup if there are no items at this point.
if ( empty( $items ) ) {
return false;
}
$nav_menu .= sprintf( $args->items_wrap, esc_attr( $wrap_id ), esc_attr( $wrap_class ), $items );
unset( $items );
if ( $show_container ) {
$nav_menu .= \'</\' . $args->container . \'>\';
}
/**
* Filters the HTML content for navigation menus.
*
* @since 3.0.0
*
* @see wp_nav_menu()
*
* @param string $nav_menu The HTML content for the navigation menu.
* @param stdClass $args An object containing wp_nav_menu() arguments.
*/
$nav_menu = apply_filters( \'wp_nav_menu\', $nav_menu, $args );
if ( $args->echo ) {
echo $nav_menu;
} else {
return $nav_menu;
}
}参考文章：https://developer.wordpress.org/reference/functions/wp_nav_menu/
