Joomla 4 : Categories::getInstance('productshop.products'); not working for my custom extension

Question

extension	title	alias
com_content	Uncategorised	uncategorised
com_banners	Sample Data-Banners	sample-data-banners
com_banners	Sample Data-Newsfeeds	sample-data-newsfeeds
com_newsfeeds	Sample Data-Contact	sample-data-contact
com_contact	Joomla!	joomla
com_productdeal.products	products Category one	products-category

If I try to print categories for Content, Banners, or Contact then getInstance function returns data correctly.

$categories = Categories::getInstance('Content');

When trying to print the categories of another custom extension, it returns nothing.

$categories = Categories::getInstance('productdeal.products');

Why can't I use custom extensions with Categories::getInstance()?

Answer 1

To use categories in your component, you need to register the 'CategoryFactory' in the 'provider' file

Example from administrator/component/com_content/services/provider.php

public function register(Container $container)
    {
        $container->set(AssociationExtensionInterface::class, new AssociationsHelper());
        $container->registerServiceProvider(new CategoryFactory('\\Joomla\\Component\\Content'));
        $container->registerServiceProvider(new MVCFactory('\\Joomla\\Component\\Content'));
        $container->registerServiceProvider(new ComponentDispatcherFactory('\\Joomla\\Component\\Content'));
        $container->registerServiceProvider(new RouterFactory('\\Joomla\\Component\\Content'));

        $container->set(
            ComponentInterface::class,
            function (Container $container) {
                $component = new ContentComponent($container->get(ComponentDispatcherFactoryInterface::class));

                $component->setRegistry($container->get(Registry::class));
                $component->setMVCFactory($container->get(MVCFactoryInterface::class));
                $component->setCategoryFactory($container->get(CategoryFactoryInterface::class));
                $component->setAssociationExtension($container->get(AssociationExtensionInterface::class));
                $component->setRouterFactory($container->get(RouterFactoryInterface::class));

                return $component;
            }
        );
    }

Also take a look at the file: administrator/component/com_content/src/Extension/ContentComponent.php