Question

has_filter( string $tag,  callable|bool $function_to_check = false )

Check if any filter has been registered for a hook.

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description

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参数

$tag

(string) (Required) The name of the filter hook.

$function_to_check

(callable|bool) (Optional) The callback to check for.

Default value: false

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返回值

(false|int) If $function_to_check is omitted, returns boolean for whether the hook has anything registered. When checking a specific function, the priority of that hook is returned, or false if the function is not attached. When using the $function_to_check argument, this function may return a non-boolean value that evaluates to false (e.g.) 0, so use the === operator for testing the return value.

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源代码

File: wp-includes/plugin.php

function has_filter($tag, $function_to_check = false) {
	global $wp_filter;

	if ( ! isset( $wp_filter[ $tag ] ) ) {
		return false;
	}

	return $wp_filter[ $tag ]->has_filter( $tag, $function_to_check );
}

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更新日志

Version	description
2.5.0	Introduced.

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相关函数

Used By

• wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::save_changeset_post()
• wp-includes/plugin.php: apply_filters_deprecated()
• wp-includes/customize/class-wp-customize-nav-menu-item-setting.php: WP_Customize_Nav_Menu_Item_Setting::preview()
• wp-admin/includes/class-wp-ms-sites-list-table.php: WP_MS_Sites_List_Table::column_plugins()
• wp-admin/includes/class-core-upgrader.php: Core_Upgrader::upgrade()
• wp-admin/includes/class-wp-ms-sites-list-table.php: WP_MS_Sites_List_Table::get_columns()
• wp-includes/capabilities.php: map_meta_cap()
• wp-includes/class-wp.php: WP::build_query_string()
• wp-includes/plugin.php: has_action()
• wp-includes/class-wp-editor.php: _WP_Editors::editor()
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User Contributed Notes

1. Skip to note content You must log in to vote on the helpfulness of this noteVote results for this note: 0You must log in to vote on the helpfulness of this note Contributed by Codex

   Basic Example

   
   <?php
   if ( ! has_filter( 'the_content', 'example_alter_the_content' ) )
       add_filter( 'the_content', 'prefix_alter_the_content' );
   ?>
   

add_filter() calls the same _wp_filter_build_unique_id() function and re-assigns the method/function parameter to the index array.

It is very likely that calling add_filter() with the same parameter list is faster than first checking if the method/function is already registered with has_filter( , ) before adding it with add_filter( , );

I am guessing the best use-case for has_filter() is to check if a filter has ANY registered methods versus checking that a specific method exists prior to re-registering it with add_filter().