The first controller

A controller is a class that answers a request: it receives the address, prepares the data and returns the page. Every page of the shop is a controller. There is no routes file in OpenCart — the address itself points to the controller file.

Where it lives

Storefront controllers are in catalog/controller/, grouped into folders by topic: product, checkout, account, information.

catalog/controller/
├── common/           header, footer, home page
├── product/          product, category, search
└── information/
    └── hello.php     the new file

While learning, the file is put next to the core controllers. Real code is packaged as an extension — the chapter about extensions moves this page into extension/acme_hello/.

Creating the controller

There is no console command. Create the file catalog/controller/information/hello.php by hand:

// catalog/controller/information/hello.php
namespace Opencart\Catalog\Controller\Information;
 
class Hello extends \Opencart\System\Engine\Controller
{
    public function index(): void
    {
        $this->response->setOutput('Hello!');
    }
}

Open http://shop.test/index.php?route=information/hello — the browser shows the word «Hello!» on an empty page. In the real file the first line is the <?php tag.

How the route maps to the file

The route parameter is the path to the file inside catalog/controller/, without the .php extension:

Address	File	Method
`index.php?route=information/hello`	`catalog/controller/information/hello.php`	`index()`
`index.php?route=product/product`	`catalog/controller/product/product.php`	`index()`
`index.php?route=checkout/cart`	`catalog/controller/checkout/cart.php`	`index()`

If the address names no method, index() is called.

Naming rules

What	Rule	Example
Namespace	`Opencart\Catalog\Controller\` plus the folder	`Opencart\Catalog\Controller\Information`
Class	File name with a capital letter	`hello.php` → `Hello`
File with an underscore	Each word capitalised, no underscore	`review_list.php` → `ReviewList`

In the admin panel the namespace starts with Opencart\Admin\Controller\.

A page with the shop design

The header and the footer of the shop are controllers too. They are called with $this->load->controller(), which returns ready HTML:

public function index(): void
{
    $header = $this->load->controller('common/header');
    $footer = $this->load->controller('common/footer');
 
    $this->response->setOutput($header . '<div class="container"><h1>Hello!</h1></div>' . $footer);
}

The same address now shows the heading between the shop menu and the footer. HTML inside PHP is only for this first example: the templates lesson moves it into a Twig file.

Common mistake

The controller prints with echo or stops with exit. The page then arrives without headers and compression, and the output order breaks. All output goes through $this->response->setOutput() — the engine sends it at the end of the request.

Thanks for reading!