add_action( string $hook_name, callable $callback, int $priority = 10, int $accepted_args = 1 ): true

Adds a callback function to an action hook.

Contents

Description

Actions are the hooks that the WordPress core launches at specific points during execution, or when specific events occur. Plugins can specify that one or more of its PHP functions are executed at these points, using the Action API.

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Parameters

$hook_name string Required
The name of the action to add the callback to.
$callback callable Required
The callback to be run when the action is called.
$priority int Optional
Used to specify the order in which the functions associated with a particular action are executed.
Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.

Default: 10

$accepted_args int Optional
The number of arguments the function accepts.

Default: 1

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Return

true Always returns true.

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More Information

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Usage

add_action( $hook, $function_to_add, $priority, $accepted_args );

To find out the number and name of arguments for an action, simply search the code base for the matching do_action() call. For example, if you are hooking into ‘save_post’, you would find it in post.php:

do_action( 'save_post', $post_ID, $post, $update );

Your add_action call would look like:

add_action( 'save_post', 'wpdocs_my_save_post', 10, 3 );

And your function would be:

function wpdocs_my_save_post( $post_ID, $post, $update ) {
   // do stuff here
}

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Source

File: wp-includes/plugin.php. View all references 

function add_action( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
	return add_filter( $hook_name, $callback, $priority, $accepted_args );
}

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Changelog

Changelog
Version Description
1.2.0 Introduced.

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User Contributed Notes

  1. Skip to note 1 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 46You must log in to vote on the helpfulness of this note
    Contributed by Codex —

    Using with a Class
    To use add_action() when your plugin or theme is built using classes, you need to use the array callable syntax. You would pass the function to add_action() as an array, with $this as the first element, then the name of the class method, like so:

    /**
 * Class WP_Docs_Class.
 */
class WP_Docs_Class {

	/**
	 * Constructor
	 */
	public function __construct() {
		add_action( 'save_post', array( $this, 'wpdocs_save_posts' ) );
	}

	/**
	 * Handle saving post data.
	 */
	public function wpdocs_save_posts() {
		// do stuff here...
	}
}

$wpdocsclass = new WP_Docs_Class();
  2. Skip to note 2 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 24You must log in to vote on the helpfulness of this note
    Contributed by Codex —

    Using with static functions in a class
    If the class is called staticly the approach has to be like below as $this is not available. This also works if class is extended. Use the following:

    /**
 * Class WP_Docs_Static_Class.
 */
class WP_Docs_Static_Class {

	/**
	 * Initializer for setting up action handler
	 */
	public static function init() {
		add_action( 'save_post', array( get_called_class(), 'wpdocs_save_posts' ) );
	}

	/**
	 * Handler for saving post data.
	 */
	public static function wpdocs_save_posts() {
		// do stuff here...
	}
}

WP_Docs_Static_Class::init();
  3. Skip to note 3 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 9You must log in to vote on the helpfulness of this note
    Contributed by Codex —

    Simple Hook
    To email some friends whenever an entry is posted on your blog:

    /**
 * Send email to my friends.
 *
 * @param int $post_id Post ID.
 * @return int Post ID.
 */
function wpdocs_email_friends( $post_id ) {
	$friends = 'bob@example.org, susie@example.org';
	wp_mail( $friends, "sally's blog updated", 'I just put something on my blog: http://blog.example.com' );

	return $post_id;
}
add_action( 'publish_post', 'wpdocs_email_friends' );
  4. Skip to note 4 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 9You must log in to vote on the helpfulness of this note
    Contributed by mkormendy —

    To pass a variable to the called function of the action, you can use closures (since PHP 5.3+) when the argument is not available in the original coded do_action. For example:

    add_action('wp_footer', function($arguments) use ($myvar) { 
    echo $myvar;
}, $priority_integer, $accepted_arguments_integer);
  6. Skip to note 6 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 3You must log in to vote on the helpfulness of this note
    Contributed by lucasbustamante —

    Passing parameters while using in a Class
    To pass parameters to your method in a Class while calling it with add_action, you can do as following:

    public function __construct() {
    // Actions
    add_action('init', array($this, 'call_somefunction'));
}

/**
 *    Intermediate function to call add_action with parameters
 */
public function call_somefunction() {
    $this->somefunction('Hello World');
}

/**
 *    Actual function that does something
 */
public function somefunction($text) {
    echo $text;
}
  7. Skip to note 7 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 3You must log in to vote on the helpfulness of this note
    Contributed by Christian Saborio —

    How to add an action that calls a function (with parameters) from an instantiated class:

    $admin_menu_hider = new AdminMenuHider( UserManagement::get_internal_users() );
			add_action(
				'wp_before_admin_bar_render',
				function () use ( $admin_menu_hider ) {
					$admin_menu_hider->change_greeting_message( 'Hello' );
				}
			);
  8. Skip to note 8 content
    You must log in to vote on the helpfulness of this noteVote results for this note: 1You must log in to vote on the helpfulness of this note
    Contributed by Codex —

    Accepted Arguments
    A hooked function can optionally accept arguments from the action call, if any are set to be passed. In this simplistic example, the echo_comment_id function takes the $comment_id argument, which is automatically passed to when the do_action() call using the comment_id_not_found filter hook is run.

    /**
 * Warn about comment not found
 *
 * @param int $comment_id Comment ID.
 */
function echo_comment_id( $comment_id ) {
	printf( 'Comment ID %s could not be found', esc_html( $comment_id ) );
}
add_action( 'comment_id_not_found', 'echo_comment_id', 10, 1 );
  9. Skip to note 9 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 Bartek —

    I urge you, don’t attach your hook callbacks inside class’ constructor.

    Instead of implementing official example most upvoted in this thread, opt for decoupled solution. You have one more line of code to write, but objects become more reusable and less error-prone (consider, what would happen if you call new WP_Docs_Class() twice in your code, following Codex example).

    /**
 * Class WP_Docs_Class.
 */
class WP_Docs_Class {
	
	/**
	 * Initiate all hooks' callbacks in a separate method.
	 */
	public function hooks() {
		add_action( 'save_post', array( $this, 'wpdocs_save_posts' ) );
	}

	/**
	 * Handle saving post data.
	 */
	public function wpdocs_save_posts() {
		// do stuff here...
	}
}

$wpdocsclass = new WP_Docs_Class();
$wpdocsclass->hooks();
  10. Skip to note 10 content
    You must log in to vote on the helpfulness of this noteVote results for this note: -4You must log in to vote on the helpfulness of this note
    Contributed by theking2 —

    To prevent runtime errors due to easy typo errors (defensive programming) and prevent pollution of the global namespace use closures instead of function names. The sample code adjusted:

    /**
 * add a save post hook
 */
add_action( 'save_post', function( $post_ID, $post, $update ) {
   // do stuff here
}, 10, 3 );

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