A Guide to Building Your Own Custom WordPress Plugin

Submitted by oretnom23 on Friday, December 8, 2023 - 17:30.

In this tutorial, we will dive into the development of a Custom WordPress Plugin using the PHP language. The primary goal is to provide students and beginners, particularly those new to WordPress and PHP, with a reference to learning useful techniques to enhance their knowledge and programming capabilities. I'll be offering sample snippets and a sample WordPress plugin source code that demonstrates our main goal in this tutorial.

What is WordPress?

WordPress is a widely utilized open-source content management system (CMS) that enables users to create and manage websites and blogs. It is written in PHP and employs a MySQL or MariaDB database. WordPress has evolved from its origins as a blogging platform to a versatile CMS utilized by individuals, businesses, and organizations for various types of websites, including blogs, portfolios, e-commerce sites, and corporate websites.

What is WordPress Plugin?

A WordPress plugin is a software component that extends and enhances the functionality of a WordPress website. Plugins are pivotal in making WordPress a flexible and customizable content management system (CMS). They enable users to incorporate specific features or capabilities into their websites without modifying the core WordPress code.

How to Create a Custom WordPress Plugin?

Step 1

To create a Custom WordPress Plugin, make a new directory in your WordPress website within the `source_code_path>wp-contents>plugins` folder. Then, create a new PHP file.

Step 2

Open your newly created PHP file with your preferred code editor, such as MS VS Code, Sublime, or Notepad++.

Step 3

Next, we need to provide the Plugin's information header at the top line of the PHP file. The information header is enclosed in comment tags. Below is an example information header for a sample WordPress Plugin:

<?php
/**
 * Plugin Name: My Custom Plugin Name
 * Plugin URI: URI of your plugin where your docs, updates, or etc located
 * Description: A brief description of yout plugin
 * Version: your plugin version
 * Author: the plugins author name
 * Author URI: the plugins author URI
 * License: license name e.g. GPL2
 */  
?>

After completing these steps, you will be able to locate your Custom WordPress Plugin on the Plugins Page of your WordPress admin side.

For a more better understanding of creating a Custom WordPress Plugin, I have developed a simple plugin that includes CRUD (Create, Read, Update, and Delete) features on the admin side. The provided plugin script also involves the creation of a new database table.

Below is the PHP script for the simple plugin I created:

<?php
/**
    * Plugin Name: My First Custom Plugin
    * Plugin URI: https://sample-domain.com
    * Description: Lorem ipsum dolor sit amet consectetur adipisicing elit.
    * Version: 1.0
    * Author: oretnom23
    * Author URI: https://www.sourcecodester.com/user/257130/activity
    * License: GPLv2 or later
    */    
 
if ( ! defined( 'ABSPATH' ) ) {
    die;
}
 
class MyFirstPlugin{
    public $notices = [];
    function __construct()
    {
        add_action( 'admin_menu', [ $this, 'pages' ] );
        add_action( 'admin_enqueue_scripts', [$this, 'bootstrap_scripts'], 10, 1 );
 
        // Process Form
        add_action( 'admin_init', [ $this, 'save_form' ] );
        add_action( 'admin_init', [ $this, 'delete_mfcp' ] );
 
        $this->notices = get_option("mfcp_notices", array());
        // print_r(gettype($this->notices));exit;
        add_action( 'admin_notices', [$this, 'display_notices'] );
    }
 
    function pages(){
        //add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position );
        add_menu_page(__('My First Custom Plugin'), __('Custom Plugin'), 'administrator', 'my-first-custom-plugin-page', [$this, 'my_plugin_list_page'], '', 25); 
        add_submenu_page('my-first-custom-plugin-page', __('Manage Plugin\'s DB'), __('Add New'), 'administrator', 'my-first-custom-plugin-page-form', [$this, 'my_plugin_form_page']); 
    }
 
    function display_notices(){
        // print_r($this->notices);exit;
        if(count($this->notices) > 0){
            foreach($this->notices as $k =>$notice){
                ?>
                <div class="notice notice-<?= $notice['type'] ?> <?= ($notice['dismissible']) ? "is-dismissible" : "" ?>">
                    <?= htmlspecialchars_decode($notice['message']) ?>
                </div>
                <?php
                unset($this->notices[$k]);
            }
        }
        update_option("mfcp_notices", []);
 
    }
    function activate(){
        // Install Plugin's Database
        $this->install_db();
    }
    function deactivate(){
        
    }
    function uninstall(){
    }
 
    /**
        * Enqueue Styles and Scripts
        */
    function bootstrap_scripts($hook){
        // Enqueue Bootstrap CDN CSS and JS only in plugin's page
        if($hook == 'toplevel_page_my-first-custom-plugin-page' || $hook == 'custom-plugin_page_my-first-custom-plugin-page-form'){
            wp_enqueue_style("fontawesome-icon-cdn","https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.1.2/css/all.min.css",[],"6.1.2", "all");
            wp_enqueue_style("bootstrap-css-cdn","https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css",[],"5.3.2", "all");
 
            wp_enqueue_script("fontawesome-icon-js-cdn","https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.1.2/js/all.min.js",[],"6.1.2", "all");
            wp_enqueue_script("bootstrap-js-cdn","https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js",[],"5.3.2", "all");
        }
        // echo $hook;exit;
    }
 
    /**
        * Create Plugin's Database
        */
    function install_db(){
        global $wpdb;
        $table = $wpdb->prefix."mfp_tbl";
        $qry = $wpdb->prepare("SHOW TABLES LIKE %s", $wpdb->esc_like($table));
        if($wpdb->get_var($qry) == $table){
            /**
                * Table Already Exists
                */
 
        }else{
            /**
                * Table Doesn't Exists on the Database
                * - Install Table
                */
            $charset_collate = $wpdb->get_charset_collate();
 
            $sql = "CREATE TABLE IF NOT EXISTS $table  (
                `id` int(30) NOT NULL PRIMARY KEY AUTO_INCREMENT,
                `meta_field` text DEFAULT NULL,
                `meta_value` text DEFAULT NULL,
                `created_at` datetime NOT NULL DEFAULT current_timestamp(),
                `updated_at` datetime DEFAULT NULL ON UPDATE current_timestamp()
            ) $charset_collate;";
            require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
            dbDelta($sql);
        }
    }
 
    /**
        * Create Plugin's Form Page
        */
    function my_plugin_form_page(){
        global $wpdb;
        if(isset($_GET['mfcp_id'])){
            $data = $wpdb->get_row(
                $wpdb->prepare("SELECT * FROM `{$wpdb->prefix}mfp_tbl` where `id` = %d", [$_GET['mfcp_id']]),
                ARRAY_A
            );
            extract($data, EXTR_PREFIX_ALL, "mfcp");
        }
        ?>
        <style>
            .card{
                max-width: unset !important;
            }
        </style>
        <div class="container-fluid">
            <div class="card shadow col-lg-5 col-md-8 col-sm-12 col-12 mx-auto p-0">
                <div class="card-header rounded-0">
                    <div class="card-title">Plugin's Sample Form <?= (!empty($mfcp_id ?? "")? " - Updating #{$mfcp_id}" : "") ?></div>
                </div>
                <div class="card-body">
                    <div class="container-fluid">
                        <form action="" id="sample-form" method="POST">
                            <?php wp_nonce_field( "mfcp-sample-form" ); ?>
                            <input type="hidden" name="action" value="save-mfcp-sample-form">
                            <input type="hidden" name="id" value="<?= $mfcp_id ?? "" ?>">
                            <div class="mb-3">
                                <label for="meta_field" class="form-label">Meta Field <small class="text-danger">*</small></label>
                                <input type="text" class="form-control rounded-0" id="meta_field" name="meta_field" value="<?= $_POST['meta_field'] ?? $mfcp_meta_field ?? "" ?>" required="required" autofocus>
                            </div>
                            <div class="mb-3">
                                <label for="meta_value" class="form-label">Meta Value <small class="text-danger">*</small></label>
                                <textarea name="meta_value" id="meta_value" rows="3" class="form-control rounded-0" requried=""><?= $_POST['meta_value'] ?? $mfcp_meta_value ?? "" ?></textarea>
                            </div>
                            <div class="mb-3">
                                <button class="btn btn-primary rounded-0" type="submit">Save</button>
                            </div>
                        </form>
                    </div>
                </div>
            </div>
        </div>
        <?
    }
 
    /**
        * Create Plugin's List Page
        */
 
    function my_plugin_list_page(){
        global $wpdb;
        $data = $wpdb->get_results(
            $wpdb->prepare("
                SELECT * FROM `{$wpdb->prefix}mfp_tbl` order by id ASC
            "),
            ARRAY_A
        );
        ?>
        <style>
            .card{
                max-width: unset !important;
            }
        </style>
        <div class="container-fluid">
            <div class="card shadow col-12 p-0">
                <div class="card-header rounded-0">
                    <div class="card-title">Plugin's Database Data</div>
                </div>
                <div class="card-body">
                    <div class="container-fluid">
                        <div class="table-responsive">
                            <table class="table table-striped table-hover table-bordered">
                                <colgroup>
                                    <col width="20%">
                                    <col width="30%">
                                    <col width="30%">
                                    <col width="20%">
                                </colgroup>
                                <thead>
                                    <tr>
                                        <th class="text-center px-2 py-1 text-light bg-primary">Date Added</th>
                                        <th class="text-center px-2 py-1 text-light bg-primary">Meta Field</th>
                                        <th class="text-center px-2 py-1 text-light bg-primary">Meta Value</th>
                                        <th class="text-center px-2 py-1 text-light bg-primary">Action</th>
                                    </tr>
                                </thead>
                                <tbody>
                                    <?php if(!empty($data)): ?>
                                    <?php foreach($data as $row): ?>
                                        <tr>
                                            <td class="px-2 py-1"><?= date("M d, Y g:i A", strtotime($row['created_at'])) ?></td>
                                            <td class="px-2 py-1"><?= $row['meta_field'] ?></td>
                                            <td class="px-2 py-1"><?= $row['meta_value'] ?></td>
                                            <td class="px-2 py-1">
                                                <div class="input-group d-flex justify-content-center">
                                                    <a href="<?= admin_url("admin.php?page=my-first-custom-plugin-page-form&mfcp_id={$row['id']}") ?>" class="btn btn-sm btn-outline-primary rounded-0" title="Edit"><i class="fa fa-edit"></i></a>
                                                    <a href="<?= admin_url("admin.php?page=my-first-custom-plugin-page-form&action=delete_mfcp&mfcp_id={$row['id']}") ?>" class="btn btn-sm btn-outline-danger rounded-0 delete-mfcp" title="Delete"><i class="fa fa-trash"></i></a>
                                                </div>
                                            </td>
                                        </tr>
                                    <?php endforeach; ?>
                                    <?php else: ?>
                                        <tr>
                                            <th class="text-center px-2 py-1" colspan="4">No Data Found!</th>
                                        </tr>
                                    <?php endif; ?>
                                </tbody>
                            </table>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        <script>
            var delete_mfcp = document.querySelectorAll('.delete-mfcp')
            delete_mfcp.forEach(el=>{
                el.addEventListener('click', function(e){
                    if(confirm(`Are you sure to delete this data?`) === false)
                    e.preventDefault();
                })
            })
        </script>
        <?
    }
    
 
    /**
        * Save Form Data
        */
    function save_form(){
        global $wpdb;
        extract($_POST, EXTR_PREFIX_ALL, "mfcp");
        $resp=[];
        if(
            isset($_POST['action']) &&
            $_POST['action'] == 'save-mfcp-sample-form'
        ){
            if(!wp_verify_nonce( $mfcp__wpnonce, 'mfcp-sample-form')){
                $resp = ["type" => "danger", "message" => "Security Check Failed!"];
            }else{
                $mfcp_meta_field = sanitize_text_field( $mfcp_meta_field );
                $mfcp_meta_value = sanitize_textarea_field( $mfcp_meta_value );
                if(empty($mfcp_id)){
                    $save = $wpdb->insert(
                        "{$wpdb->prefix}mfp_tbl",
                        [
                            "meta_field" => $mfcp_meta_field,
                            "meta_value" => $mfcp_meta_value
                        ],
                        [
                            '%s',
                            '%s'
                        ]
                    );
                }else{
                    $save = $wpdb->update("{$wpdb->prefix}mfp_tbl",
                    [
                        "meta_field" => $mfcp_meta_field,
                        "meta_value" => $mfcp_meta_value
                    ],
                    [
                        "id" => $mfcp_id,
                    ],
                    [
                        '%s',
                        '%s'
                    ],
                    [
                        '%d',
                    ]
                    );
                }
                if($wpdb->last_error){
                    $resp = ["type" => "danger", "message" => $wpdb->last_error];
                }else{
                    $resp = ["type" => "success", "message" => "Data has been saved successfully!"];
                }
            }
            
            $this->notices[] = $resp;
            update_option("mfcp_notices", $this->notices);
            echo "<script>location.replace(`".admin_url("admin.php?page=my-first-custom-plugin-page")."`)</script>";
            exit;
        }
 
    }
 
    /**
        * Delete Data
        */
    function delete_mfcp(){
        global $wpdb;
        if(
            isset($_GET['page']) && 
            $_GET['page'] == 'my-first-custom-plugin-page-form' &&
            isset($_GET['action']) && 
            $_GET['action'] == 'delete_mfcp'&&
            isset($_GET['mfcp_id'])
        ){
            $delete = $wpdb->delete("{$wpdb->prefix}mfp_tbl", [ "id" =>  $_GET['mfcp_id']], ['%d']);
            if($wpdb->last_error){
                $resp = ["type" => "danger", "message" => $wpdb->last_error];
            }else{
                $resp = ["type" => "success", "message" => "Data has been deleted successfully!"];
            }
            $this->notices[] = $resp;
            update_option("mfcp_notices", $this->notices);
            echo "<script>location.replace(document.referrer)</script>";
            exit;
        }
    }
    
}
 
if(class_exists("MyFirstPlugin")){
    $MyFirstPlugin = new MyFirstPlugin();
    register_activation_hook(__FILE__ , array ( $MyFirstPlugin , 'activate' ) );
}
    

Snapshots

Explore the snapshots below, capturing the results of the Custom WordPress Plugin Script provided above:

Plugin's Custom Form Page

Plugin's Custom List Page

And there you have it! I trust this Custom WordPress Plugin Guide proves helpful for your needs and becomes a valuable resource for your current and future WordPress projects.

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