Understanding cakephp3 error handling - error-handling

Question

I want to create a maintenance Page for my cake website by checking a Database Table for a maintenance flag using a sub-function of my AppController "initilize()" method. If the flag is set, i throw my custom MaintenanceException(Currently containing nothing special):
class MaintenanceException extends Exception{
}
To handle it, I implemented a custom App Exception Renderer:
class AppExceptionRenderer extends ExceptionRenderer {
public function maintenance($error)
{
return "MAINTENANCE";
}
}
I am able to see this maintenance Text on my website if I set my DB flag to true, but I could not find any information in cake's error handling documentation (http://book.cakephp.org/3.0/en/development/errors.html) on how I can actually tell the Exception renderer to render view "maintenance" with Template "infopage".
Can I even us that function using the ExceptionRenderer without a custom error controller? And If not, how should a proper ErrorController implementation look like? I already tried this:
class AppExceptionRenderer extends ExceptionRenderer {
protected function _getController(){
return new ErrorController();
}
public function maintenance($error)
{
return $this->_getController()->maintenanceAction();
}
}
together with:
class ErrorController extends Controller {
public function __construct($request = null, $response = null) {
parent::__construct($request, $response);
if (count(Router::extensions()) &&
!isset($this->RequestHandler)
) {
$this->loadComponent('RequestHandler');
}
$eventManager = $this->eventManager();
if (isset($this->Auth)) {
$eventManager->detach($this->Auth);
}
if (isset($this->Security)) {
$eventManager->detach($this->Security);
}
$this->viewPath = 'Error';
}
public function maintenanceAction(){
return $this->render('maintenance','infopage');
}
}
But this only throws NullPointerExceptions and a fatal error. I am really dissapointed by the cake manual as well, because the code examples there are nowhere close to give me an impression of how anything could be done and what functionality I actually have.

Answer 1

Because I had some more time today, I spent an hour digging into the cake Source and found a solution that works well for me (and is propably the way it should be done, altough the cake documentation does not really give a hint):
Step 1: Override the _template(...)-Method of the ExceptionRenderer in your own class. In my case, I copied the Method of the parent and added the following Code at the beginning of the method:
$isMaintenanceException = $exception instanceof MaintenanceException;
if($isMaintenanceException){
$template = 'maintenance';
return $this->template = $template;
}
This tells our Renderer, that the error Template called "maintentance"(which should be located in Folder: /Error) is the Error Page content it should render.
Step 2: The only thing we have to do now (And its is kinda hacky in my opinion, but proposed by the cake documentation in this exact way) is to set the layout param in our template to the name of the base layout we want to render with. So just add the following code on top of your error template:
$this->layout = "infopage";
The error controller I created is actually not even needed with this approach, and I still don't know how the cake error controller actually works. maybe I will dig into this if I have more time, but for the moment.