namespace DrupalmymoduleController;

use DrupalCoreControllerControllerBase;

class ExampleController extends ControllerBase {

  /**
   * Controller for action button.
   */
  public function action() {
    // if user is not logged in, redirect to create a new account
    if ($this->currentUser()->isAnonymous()) {
      return $this->redirect('user.register');
    }
    // return content or redirect to content
    return ...;
  }

}