WordPress: Register shortcodes with Class and Interfaces

class-example-shortcode.php

<?php
/**
 * @package DlmWpTheme
 */

// Exit if accessed directly.
defined('ABSPATH') || exit;

require_once dirname(__FILE__) . '/class-interface-package.php';
require_once dirname(__FILE__) . '/class-interface-package-shortcode.php';

// Todo: Change your class name

class MY__ShortcodeClass implements Dlm__PackageInterface, Dlm__ShortcodeInterface {
    private $atts = [];
    private $postType = "my_cpt";

    function __construct() {}

    /**
     * Put all relevant methods in the init function
     */
    public function init() {
        // $this->someFunctions();
        return $this->renderOutput();
    }

    /**
     * Used in shortcode function
     */
    public function setAttributes($atts) {
        $this->atts = $atts;
    }

    /**
     * 
     */
    protected function getPosts() {
        $posts = get_posts(array(
            'post_type' => $this->postType,
            'post_status'   => 'publish',
            'posts_per_page' => -1,
            'meta_key' => 'MY_CUSTOM_FIELD',
            // If a numberic field
            // 'meta_type' => 'NUMERIC',
            // 'orderby' => 'meta_value meta_value_num',
            'orderby' => 'meta_value',
            'order' => 'ASC',
        ));

        return $posts;
    }

    /**
     * Get all posts and render it for the shortcode
     */
    public function renderOutput() {
        $posts = $this->getPosts();

        ob_start();
        include dirname(__FILE__) . '/partials/default.php';
        $output = ob_get_contents();
        ob_get_clean();

        return $output;
    }

    /**
     * Register the shortcode in wordpress
     */
    public function activateShortcode() {
        // 
        add_shortcode( 'my-custom-shortcode', [ $this, 'shortcodeFunc' ] );
    }
    
    /**
     * @return 
     */
    public function shortcodeFunc( $atts = [], $content = null ) {
        $atts = array_change_key_case((array)$atts, CASE_LOWER);
        $this->setAttributes($atts);
        return $this->init();
    }
}

// Todo: Change your class name
(new MY__ShortcodeClass())->activateShortcode();

class-interface-package-shortcode.php

<?php
/**
 * Interface for shortcode packages
 * To activate the shortcode > 
 * Use (new MY__ClassName())->activateShortcode();
 * 
 * @package DlmWpTheme
 */

// Exit if accessed directly.
defined('ABSPATH') || exit;

interface Dlm__ShortcodeInterface {

    public function setAttributes(array $atts);

    public function activateShortcode();
    
    public function shortcodeFunc( $atts = [], $content = null );
}

class-interface-package.php

<?php
/**
 * Interface for packages
 * 
 * @package DlmWpTheme
 */

// Exit if accessed directly.
defined('ABSPATH') || exit;

interface Dlm__PackageInterface {

    public function init();

    public function renderOutput();
}