The request and response objects should be registered with the controller, as should be any additional optional arguments; these will be available via \getRequest(), \getResponse(), and \getInvokeArgs(), respectively.

When overriding the constructor, please consider this usage as a best practice and ensure that each is registered appropriately; the easiest way to do so is to simply call parent::__construct($request, $response, $invokeArgs).

After the request, response, and invokeArgs are set, the \$_helper is initialized.

Finally, \init() is called as the final action of instantiation, and may be safely overridden to perform initialization tasks; as a general rule, override \init() instead of the constructor to customize an action controller's instantiation.