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Description

Hooks a function on to a specific action.

More specifically, this function will run the function $function_to_add when the event $hook occurs.

This function is an alias to add_filter().

See Plugin API/Action Reference for a list of action hooks. Actions are (usually) triggered when the WordPress core calls do_action().

Usage

<?php add_action( $hook, $function_to_add, $priority, $accepted_args ); ?>

Parameters

$hook

(string) (required) The name of the action to which $function_to_add is hooked. (See Plugin API/Action Reference for a list of action hooks). Can also be the name of an action inside a theme or plugin file, or the special tag "all", in which case the function will be called for all hooks.

Default: None

$function_to_add

(callback) (required) The name of the function you wish to be hooked.

Default: None

$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 hooked function accepts. In WordPress 1.5.1+, hooked functions can take extra arguments that are set when the matching do_action() or apply_filters() call is run. For example, the action comment_id_not_found will pass any functions that hook onto it the ID of the requested comment.

Default: 1

Return Values

(boolean): Always True.

Examples

Simple Hook

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

function 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', 'email_friends' );

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.

function echo_comment_id( $comment_id ) {
   echo 'Comment ID ' . $comment_id . ' could not be found';
}
add_action( 'comment_id_not_found', 'echo_comment_id', 10, 1 );

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 MyPluginClass {

    public function __construct() {

         add_action( 'save_post', array( $this, 'myplugin_save_posts' ) );
    }
    
    public function myplugin_save_posts() {
         // do stuff here...
    }
}

$mypluginclass = new MyPluginClass();

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 MyPluginClass {

    public static function init() {

         add_action( 'save_post', array( get_called_class(), 'myplugin_save_posts' ) );
    }
    
    public static function myplugin_save_posts() {
         // do stuff here...
    }
}

MyPluginClass::init();

Notes

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: <?php do_action( 'save_post', $post_ID, $post, $update ); ?>

Your add_action call would look like: <?php add_action( 'save_post', 'my_save_post', 10, 3 ); ?>

And your function would be:

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

Change Log

Since 1.2.0

Source File

add_action() is located in wp-includes/plugin.php.

WordPress.org

Codex

Function Reference/add action

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