Book Image

WordPress Plugin Development Cookbook - Second Edition

By : Yannick Lefebvre
Book Image

WordPress Plugin Development Cookbook - Second Edition

By: Yannick Lefebvre

Overview of this book

WordPress is a popular, powerful, and open Content Management System. Learning how to extend its capabilities allows you to unleash its full potential, whether you're an administrator trying to find the right extension, a developer with a great idea to enhance the platform for the community, or a website developer working to fulfill a client's needs. This book shows readers how to navigate WordPress' vast set of API functions to create high-quality plugins with easy-to-configure administration interfaces. With new recipes and materials updated for the latest versions of WordPress 4.x, this second edition teaches you how to create plugins of varying complexity ranging from a few lines of code to complex extensions that provide intricate new capabilities. You'll start by using the basic mechanisms provided in WordPress to create plugins and execute custom user code. You will then see how to design administration panels, enhance the post editor with custom fields, store custom data, and modify site behavior based on the value of custom fields. You'll safely incorporate dynamic elements on web pages using scripting languages, and build new widgets that users will be able to add to WordPress sidebars and widget areas. By the end of this book, you will be able to create WordPress plugins to perform any task you can imagine.

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Table of Contents (20 chapters)
Title Page
Title Page
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Dedication
Dedication
Preface
Preface
Free Chapter
1
Preparing a Local Development Environment
Preparing a Local Development Environment
Introduction
Installing a web server on your computer
Downloading and configuring a local WordPress installation
Creating a local Subversion repository
Importing initial files to a local Subversion repository
Checking out files from a Subversion repository
Committing changes to a Subversion repository
Installing a dedicated code editor/text editor
2
Plugin Framework Basics
Plugin Framework Basics
Introduction
Creating a plugin file and header
Adding output content to page headers using plugin actions
Using WordPress path utility functions to load external files and images
Modifying the site generator meta tag using plugin filters
Adding text after each item's content using plugin filters
Inserting link statistics tracking code in page body using plugin filters
Troubleshooting coding errors and printing variable content
Creating a new simple shortcode
Creating a new shortcode with parameters
Creating a new enclosing shortcode
Loading a style sheet to format plugin output
Writing plugins using object-oriented PHP
3
User Settings and Administration Pages
User Settings and Administration Pages
Introduction
Creating default user settings on plugin initialization
Storing user settings using arrays
Removing plugin data on deletion
Creating an administration page menu item in the settings menu
Creating a multi-level administration menu
Adding menu items leading to external pages
Hiding items which users should not access from the default menu
Rendering the admin page contents using HTML
Processing and storing plugin configuration data
Displaying a confirmation message when options are saved
Adding custom help pages
Rendering the admin page contents using the Settings API
Accessing user settings from action and filter hooks
Formatting admin pages using meta boxes
Splitting admin code from the main plugin file to optimize site performance
Storing style sheet data in user settings
Managing multiple sets of user settings from a single admin page
Creating network-level admin pages
4
The Power of Custom Post Types
The Power of Custom Post Types
Introduction
Creating a custom post type
Adding a new section to the custom post type editor
Displaying single custom post type items using a custom layout
Displaying custom post type data in shortcodes
Adding custom categories for custom post types
Adding custom fields to categories
Hiding the category editor from the custom post type editor
Displaying additional columns in the custom post list page
Adding filters for custom categories to the custom post list page
Adding Quick Edit fields for custom categories
Updating page title to include custom post data using plugin filters
5
Customizing Post and Page Editors
Customizing Post and Page Editors
Introduction
Capturing and displaying information using custom meta boxes
Displaying custom post data using filter functions
Hiding the Custom Field section in the post editor
Extending the post editor to allow users to upload files directly
6
Accepting User Content Submissions
Accepting User Content Submissions
Introduction
Creating a client-side content submission form
Saving user-submitted content in custom post types
Sending email notifications upon new submissions
Implementing a CAPTCHA on user forms using an online service
Using a local library to implement a CAPTCHA on user forms
7
Customizing User Data
Customizing User Data
Introduction
Adding custom fields to the user editor
Processing and storing user custom data
Displaying new user data in user list page
Using custom user data in containing shortcode
8
Creating Custom MySQL Database Tables
Creating Custom MySQL Database Tables
Introduction
Creating new database tables
Deleting custom tables on plugin removal
Updating custom table structure on plugin upgrade
Displaying custom table data on an admin page
Inserting and updating records in custom tables
Deleting records from custom tables
Displaying custom database table data in shortcodes
Implementing a search function to retrieve custom table data
Importing data from a user file into custom tables
9
Leveraging JavaScript, jQuery, and AJAX Scripts
Leveraging JavaScript, jQuery, and AJAX Scripts
Introduction
Safely loading jQuery onto WordPress web pages
Displaying a pop-up dialog using the built-in ThickBox plugin
Controlling pop-up dialog display using shortcodes
Displaying a calendar day selector using the Datepicker plugin
Adding tooltips to admin page form fields using the TipTip plugin
Using AJAX to dynamically update partial page contents
10
Adding New Widgets to the WordPress Library
Adding New Widgets to the WordPress Library
Introduction
Creating a new widget in WordPress
Displaying configuration options
Validating configuration options
Implementing the widget display function
Adding a custom dashboard widget
Adding a custom widget to the network dashboard
11
Enabling Plugin Internationalization
Enabling Plugin Internationalization
Introduction
Changing the WordPress language configuration
Adapting default user settings for translation
Making admin page code ready for translation
Modifying shortcode output for translation
Translating text strings using Poedit
Loading a language file in the plugin initialization
12
Distributing Your Plugin on wordpress.org
Distributing Your Plugin on wordpress.org
Introduction
Creating a README file for your plugin
Applying for your plugin to be hosted on WordPress.org
Uploading your plugin using Subversion
Providing plugin banner and thumbnail images

Using WordPress path utility functions to load external files and images

On occasion, plugins need to refer to external files (for example, images, JavaScript, or jQuery script files) that are stored in the plugin directory. Since users are free to rename a plugin's folder or even install plugin files straight into the WordPress plugin directory, paths to any external files must be built dynamically based on the actual plugin location. Thankfully, a number of utility functions are present to simplify this task. In this recipe, we will write a simple plugin that will add a favicon meta tag to a website's header, pointing to an image file located in the plugin directory.

How to do it...

  1. Navigate to the WordPress plugin directory of your development installation.
  2. Create a new directory called ch2-favicon.
  3. Use a web service, such as http://getfavicon.org, to retrieve a website's favicon (for example, http://www.packtpub.com) and store it in the plugin directory with its default name (favicon.ico...
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