Using a private method as an action callback from within a class

Question

I have created a class from within which I would like to call a private method (from within the same class) from the __construct method as an action callback.

When I would like to use a public method I can access it by:

add_action( 'init', array( $this, 'action_callback' ) );

However, this causes an error when the method is private. I have also tried unsuccessfully:

add_action('init', $this->action_callback() );

How do I access a private method?

The class looks something like:

class My_class {
    public function __construct() {
        add_action( 'init', array( $this, 'action_callback' ) );
    }

    private function action_callback() {
        // do something
    }
}

Answer 1

It's not possible to call a private method through an action or filter. When calling add_action or add_filter, WordPress adds the callback to a list of callbacks for that specific action or filter. Then, when do_action or apply_filters is called, WordPress uses call_user_func_array to call the linked functions and methods. As call_user_func_array is not called from within the class, it can't call private methods of that class.

Furthermore, there's no proper way to really keep the method private, even though you could add a separate (public) method to your class, add that as a callback to the action, and have that call the private method. In doing that, however, you lose the real concept of the method being private.