Component: structure and entry point

A component is the largest Joomla extension: a section with its own pages, database tables and control panel screens. We start the com_hello component — a simple blog with posts. This lesson creates its skeleton: the manifest and the provider. Pages appear in the next one.

Two folders

A component has two parts, and they live in different places of the site:

administrator/components/com_hello/     the control panel part
├── hello.xml                           the manifest
├── services/
│   └── provider.php                    the entry point — one for both parts
├── src/                                panel classes
└── tmpl/                               panel layouts
 
components/com_hello/                   the site part
├── src/                                site classes
└── tmpl/                               site layouts

Create these folders by hand. The manifest and the provider always live in the administrator part — even if the component works only on the site.

The manifest

<?xml version="1.0" encoding="UTF-8"?>
<!-- administrator/components/com_hello/hello.xml -->
<extension type="component" method="upgrade">
    <name>com_hello</name>
    <version>1.0.0</version>
    <description>A learning blog</description>
    <namespace path="src">My\Component\Hello</namespace>
 
    <files folder="site">
        <folder>src</folder>
        <folder>tmpl</folder>
    </files>
 
    <administration>
        <menu>Hello</menu>
 
        <files folder="administrator">
            <folder>services</folder>
            <folder>src</folder>
            <folder>tmpl</folder>
        </files>
    </administration>
</extension>

Manifest part	Purpose
The first `files` section	Files of the site part
The `administration` section	Everything that belongs to the panel
`menu`	The item name in the Components menu of the panel
The `folder` attributes	Folders in the ZIP archive the installer takes files from

Namespace

The manifest has one namespace, and Joomla splits it into parts itself:

Namespace	Folder
`My\Component\Hello\Site`	`components/com_hello/src`
`My\Component\Hello\Administrator`	`administrator/components/com_hello/src`
`My\Component\Hello\Api`	`api/components/com_hello/src`

The provider

// administrator/components/com_hello/services/provider.php
defined('_JEXEC') or die;
 
use Joomla\CMS\Dispatcher\ComponentDispatcherFactoryInterface;
use Joomla\CMS\Extension\ComponentInterface;
use Joomla\CMS\Extension\MVCComponent;
use Joomla\CMS\Extension\Service\Provider\ComponentDispatcherFactory;
use Joomla\CMS\Extension\Service\Provider\MVCFactory;
use Joomla\CMS\MVC\Factory\MVCFactoryInterface;
use Joomla\DI\Container;
use Joomla\DI\ServiceProviderInterface;
 
return new class () implements ServiceProviderInterface {
    public function register(Container $container): void
    {
        $container->registerServiceProvider(new MVCFactory('\\My\\Component\\Hello'));
        $container->registerServiceProvider(new ComponentDispatcherFactory('\\My\\Component\\Hello'));
 
        $container->set(
            ComponentInterface::class,
            function (Container $container) {
                $component = new MVCComponent($container->get(ComponentDispatcherFactoryInterface::class));
                $component->setMVCFactory($container->get(MVCFactoryInterface::class));
 
                return $component;
            },
        );
    }
};

When a request with option=com_hello arrives, Joomla runs this file. MVCFactory knows how to create the component's controllers, models and views by name, and MVCComponent is a ready-made class for a component built on the MVC pattern.

The MVC pattern

Part	Folder in `src`	What it does
Controller	`Controller`	Receives the request and decides what to do
Model	`Model`	Fetches and saves data
View	`View`	Takes data from the model and passes it to the layout
Layout	`tmpl` (next to `src`)	Outputs HTML

Installing

Open System → Install → Discover, press Discover and install com_hello. The Components menu of the panel gets a "Hello" item. For now it leads to an error page: the component has no controllers yet. The next lesson fixes that.

Common mistake

The manifest is placed in components/com_hello — by analogy with a module. Discover does not find such a component: Joomla looks for a component manifest only in administrator/components/com_hello. The services folder must be there as well.

Thanks for reading!