MyController.php

<?php
namespace Karen\Controller;

use \Psr\Http\Message\ServerRequestInterface as Request;
use \Psr\Http\Message\ResponseInterface as Response;

abstract class MyController
{
    protected $app;
    protected $container;
    protected $request;
    protected $response;

    public function __construct($app)
    {
        $this->app = $app;
        $this->container = $app->getContainer();
        $this->setErrorHandler();
    }

    public abstract function action($args);

    public function __invoke(Request $request,  Response $response, $args)
    {
        $this->request = $request;
        $this->response = $response;
        return $this->action($args);
    }

    public function setErrorHandler()
    {
        $this->container['errorHandler'] = function ($c) {
            return function ($request, $response, $exception) use ($c) {
                return $c['response']->withStatus(500)
                    ->withHeader('Content-Type', 'text/html')
                    ->write('Something went wrong!');
            };
        };
    }

    public function render($output)
    {
        return $this->response->write($output);
    }

    public function render404($output)
    {
        return $this->response->withStatus(404)->write($output);
    }

}