class MyForm
{

    // public $onSuccess = [];
    public $onSomeAction = [];


    public function __construct()
    {
        parent::__construct();

        // $this->addText();

        $this->onSuccess[] = function () {
            $this->onSomeAction($this);
        }
    }

}

$form = new MyForm;
$form->onSuccess[] = function () {
    $this->redirect();
};