hooks.md

WordPress Hooks

• Workflow
• add_action()
• do_action()
• do_action_ref_array()
• remove_action()

Integration with Classes:

• Hook Being Class Static Method
• Hook Being Class Instance Method
• Hook Being Method of a Singleton
• Hook Added/Removed within Class
  • Addition and Definition within Instance Methods
  • Addition and Definition within Static Methods
  • Addition within Instance Method and Definition within Static Method
  • Addition within Static Method and Definition within Instance Method

Workflow

• add action with add_action()
• invoke action with do_action() or do_action_ref_array()

Hooks are not meant to return any value, they should only execute some code.

add_action($name, $function, $priority, $accepted_args)

• $function as a string

add_action('prfx_plugin_pre_setup', 'pre_setup_fn', 10, 2);

function pre_setup_fn($a, $b) {
  echo $a + $b;
}

• $function as a function

add_action('prfx_plugin_pre_setup', function ($a, $b) {
  echo $a + $b;
}, 10, 2);

$pre_setup_fn = function ($a, $b) {
  echo $a + $b;
};

add_action('prfx_plugin_pre_setup', $pre_setup_fn, 10, 2);

do_action($name, ...$args)

do_action('prfx_plugin_pre_setup', 1, 2);

do_action_ref_array($name, $args_arr)

This function is identical to add_action(), but arguments are passed an an array.

do_action_ref_array('prfx_plugin_pre_setup', [1, 2]);

remove_action($name, $function, $priority)

Priority can be omitted, but if it's passed and differs from original one passed to the add_action(), an action will not be removed.

• action with $function passed as a string

add_action('prfx_plugin_pre_setup', 'pre_setup_fn', 10, 2);

...

remove_action('prfx_plugin_pre_setup', 'pre_setup_fn');

• action with $function passed as a function

add_action('prfx_plugin_pre_setup', $pre_setup_fn, 10, 2);

...

remove_action('prfx_plugin_pre_setup', $pre_setup_fn);

Note that remove_action() must be called inside a function and cannot be called directly:

add_action('wp_head', function () {
  remove_action('wp_footer', 'no_longer_needed_action');
});

Hook Being Class Static Method

class Hook {
  public static function calc_hook($a, $b) {
    echo $a + $b;
  }
}

add_action('prfx_plugin_pre_setup', ['Hook', 'calc_hook'], 10, 2);
...
remove_action('prfx_plugin_pre_setup', ['Hook', 'calc_hook']);

Hook Being Class Instance Method

class Hook {
  public function calc_hook($a, $b) {
    echo $a + $b;
  }
}

$hook = new Hook();

add_action('prfx_plugin_pre_setup', [$hook, 'calc_hook'], 10, 2);
...
remove_action('prfx_plugin_pre_setup', [$hook, 'calc_hook']);

Hook Being Method of a Singleton

class Hook {
  private static $_instance = null;

  private function __construct() {}

  public static function getInstance() {
    if (is_null(self::$_instance)) {
      self::$_instance = new self();
    }

    return self::$_instance;
  }

  public function calc_hook($a, $b) {
    echo $a + $b;
  }
}

add_action('prfx_plugin_pre_setup', [Hook::getInstance(), 'calc_hook'], 10, 2);
...
remove_action('prfx_plugin_pre_setup', [Hook::getInstance(), 'calc_hook']);

Hook Added/Removed within Class

Addition and Definition within Instance Methods

class Hook {
  public function addHooks() {
    add_action('prfx_plugin_pre_setup', [$this, 'calc_hook'], 10, 2);
  }

  public function removeHooks() {
    remove_action('prfx_plugin_pre_setup', [$this, 'calc_hook']);
  }

  public function calc_hook($a, $b) {
    echo $a + $b;
  }
}

$hook = new Hook();

$hook->addHooks();
...
$hook->removeHooks();

Addition and Definition within Static Methods

class Hook {
  public static function addHooks() {
    add_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook'], 10, 2);
  }

  public static function removeHooks() {
    remove_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook']);
  }

  public static function calc_hook($a, $b) {
    echo $a + $b;
  }
}

Hook::addHooks();
...
Hook::removeHooks();

Addition within Instance Method and Definition within Static Method

class Hook {
  public function addHooks() {
    add_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook'], 10, 2);
  }

  public function removeHooks() {
    remove_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook']);
  }

  public static function calc_hook($a, $b) {
    echo $a + $b;
  }
}

$hook = new Hook();

$hook->addHooks();
...
$hook->removeHooks();

Addition within Static Method and Definition within Instance Method

class Hook {
  public static function addHooks() {
    add_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook'], 10, 2);
  }

  public static function removeHooks() {
    remove_action('prfx_plugin_pre_setup', [get_called_class(), 'calc_hook']);
  }

  public function calc_hook($a, $b) {
    echo $a + $b;
  }
}

$hook = new Hook();

$hook::addHooks();
# or: Hook::addHooks()
...
$hook::removeHooks();
# or: Hook::removeHooks()