Professional WordPress Plugin Development

Full Table of Content

Chapter 0: Foreword by a very famous WordPress rockstar

Chapter 1: An Introduction to Plugins

What Is a Plugin?

• How Plugins Interact with WordPress
• When Are Plugins Loaded?

Available Plugins

• Official Plugin Directory
• Popular Plugin Examples
• Popular Plugin Tags

Advantages of Plugins

• Not Modifying Core
• Why Reinvent the Wheel
• Separating Plugins and Themes
• Easy Updates
• Easier to Share and Reuse
• Plugin Sandbox
• Plugin Community

Installing and Managing Plugins

• Installing a Plugin
• Managing Plugins
• Editing Plugins
• Plugin Directories
• Types of Plugins
• Testing Plugin Functionality

Summary

Chapter 2: Plugin Foundation

Creating a Plugin File

• Naming Your Plugin
• Using a Folder

Sanity Practices

• Prefix Everything
• File Organization
• Folder Structure

Header Requirements

• Creating the Header
• Plugin License

Determining Paths

• Plugin Paths
• Local Paths
• URL Paths

Activate/Deactivate Functions

• Plugin Activation Function
• Create Default Settings on Activate
• Plugin Deactivation Function
• Deactivate Is Not Uninstall

Uninstall Methods

• Why Uninstall Is Necessary
• Uninstall.php
• Uninstall Hook

Coding Standards

• Document Your Code
• Naming Variables, Functions, and Files
• Single and Double Quotes
• Indentation
• Brace Style
• Space Usage
• Shorthand PHP
• SQL Statements

Plugin Development Checklist

Summary

Chapter 3: Hooks

Actions

• What Is an Action?
• Action Hook Functions
• Commonly Used Action Hooks

Filters

• What Is a Filter?
• Filter Hook Functions
• Quick Return Functions
• Commonly Used Filter Hooks

Using Hooks from Within a Class

Creating Custom Hooks

• Benefits of Creating Custom Hooks
• Custom Action Hook Example
• Custom Filter Hook Example

How to Find Hooks

• Searching for Hooks in the Core Code
• Variable Hooks
• Hook Reference Lists

Summary

Chapter 4: Integrating in WordPress

Adding Menus and Submenus

• Creating a Top-Level Menu
• Adding a Submenu
• Adding a Menu Item to an Existing Menu

Creating Widgets

• Creating a Widget
• Advanced Widget
• Creating Dashboard Widgets
• Creating a Dashboard Widget with Options

Meta Boxes

• What Is a Meta Box?
• Adding a Custom Meta Box
• Saving Meta Box Data
• Advanced Meta Box

Keeping It Consistent

• Using the WordPress UI
• Headings
• Icons
• Messages
• Buttons
• Links
• Form Fields
• Tables
• Pagination

Summary

Chapter 5: Internationalization

Internationalization and Localization

• Why Internationalize?
• Understanding Internationalization in Professional Work
• Getting Your Plugin Ready for Translation
• Echoing and Returning Strings
• Using Placeholders
• Internationalizing JavaScript

Creating Translation Files

• The MO and PO Files
• Translation Tools
• How to Create a POT File
• Where to Store Translation Files

Summary

Chapter 6: Plugin Security

Securing Your Plugin

• What Securing Your Plugin Is
• What Securing Your Plugin Is Not

User Permissions

• How to Check current_user_can
• Do Not Check Too Early

Nonces

• Authority Versus Intention
• What Is a Nonce?
• How to Create and Verify Nonces
• Nonces in AJAX Scripts

Data Validation and Sanitization

• The Need for Data Validation and Sanitization
• Good Practice: Identifying Potentially Tainted Data
• Validating or Sanitizing Input?
• Validating and Sanitizing Cookbook

Formatting SQL Statements

• The $wpdb Object
• Why wpdb Methods Are Superior
• All-in-One Methods
• Common Methods
• Protecting Queries Against SQL Injections
• Miscellaneous wpdb Methods and Properties

Security Good Habits

Summary

Chapter 7: Plugin Settings

The Options API

• Saving Options
• Saving an Array of Options
• Retrieving Options
• Loading an Array of Options
• Deleting Options
• The Autoload Parameter

The Settings API

• Benefits of the Settings API
• Settings API Functions
• Wrapping It Up: A Complete Plugin Management Page
• Improving Feedback on Validation Errors
• Adding Fields to an Existing Page

The Transients API

• Saving an Expiring Option
• Retrieving an Expiring Option
• Deleting an Expiring Option
• A Practical Example Using Transients
• Technical Details and Tip
• Transient Ideas

Saving Per-User Settings

• Craft a Plugin
• User Metadata
• Saving User Metadata
• Updating User Metadata
• Getting User Metadata
• Deleting User Metadata
• Getting a User’s ID
• Adding Input Fields to a Profile Page
• BOJ’s Admin Lang Plugin
• Per-User Settings: Best Practices

Storing Data in Custom Tables

• Types of Data
• WordPress’ Standard Tables
• Creating a Custom Table
• Updating the Structure of a Custom Table
• dbDelta() Tips for Success
• Accessing Your Custom Table

Summary

Chapter 8: Users

Working with Users

• User Functions
• Creating, Updating, and Deleting Users
• User Data
• User Metadata

Roles and Capabilities

• What Are Roles and Capabilities?
• Default Roles
• Custom Roles

Limiting Access

• Checking User Permissions
• Is the User an Admin?
• Allowing Custom Permissions

Customizing Roles

• Creating a Role
• Deleting a Role
• Adding Capabilities to a Role
• Removing Capabilities from a Role
• A Custom Role and Capability Plugin

Summary

Chapter 9: HTTP API

HTTP Requests Crash Course

• What Is an HTTP Request?
• How to Make HTTP Requests in PHP

WordPress’ HTTP Functions

• The wp_remote_ Functions
• Advanced Configuration and Tips

Practice: Reading JSON from a Remote API

• Getting and Reading JSON
• Your Functional Plugin

Practice: Sending Data to a Remote API

• Formatting Parameters for POST Requests
• Your Functional Plugin

Practice: Reading Arbitrary Content

Make Your Own Plugin Repository

• How Plugin Upgrades Work in WordPress
• Polling an Alternative API from a Plugin
• Building the Alternative API
• A Few Words of Caution About Self-Hosted API

Special Case: Fetching Remote Feeds

Summary

Chapter 10: The Shortcode API

Creating Shortcodes

• What Shortcodes Are
• Register Custom Shortcodes

Shortcode Tips

• Think Simplicity for the User
• Remember the Dynamicity
• Look Under the Hoods
• A “bb code” for Comments Plugin
• Shortcode Nesting Limitations

Integrating Google Maps

• Accessing the Google Geocoding API
• Storing API Results
• Accessing the Google Maps API

More Shortcode Quick Ideas

• Display Member-Only Content
• Display Time-Limited Content
• Obfuscate Email Addresses

Summary

Chapter 11: Extending Posts: Meta Data, Custom Post Types, and Taxonomies

Creating Custom Post Types

• Post Type Possibilities
• Registering a Post Type
• Setting Post Type Labels
• Using Custom Capabilities
• Attaching Existing Taxonomies

Using Custom Post Types

• Creating a Custom Post Type Loop
• Retrieving Custom Post Type Content
• Checking if Post Type Exists

Post Meta Data

• Adding Post Meta Data
• Retrieving Post Meta Data
• Updating Post Meta Data
• Deleting Post Meta Data

Creating Custom Taxonomies

• Understanding Taxonomies
• Registering a Custom Taxonomy
• Assigning a Taxonomy to a Post Type

Using Custom Taxonomies

• Retrieving a Taxonomy
• Using a Taxonomy with Posts
• Taxonomy Conditional Tags

A Post Type and Taxonomy Plugin

Summary

Chapter 12: JavaScript and Ajax in WordPress

jQuery–A Brief Introduction

• Benefits of Using jQuery
• jQuery Crash Course

Ajax

• What Is Ajax?
• Ajax Best Practices

Adding JavaScript in WordPress

• A Proper Way to Include Scripts
• Where to Include Scripts
• Adding Scripts Only When Needed
• Dynamic Scripts in WordPress

Ajax in WordPress

• Ajax in WordPress: Principles
• A Complete Example: Instant “Read More” Links
• Another Example: Frontend Comment Deletion
• Debugging Ajax

Summary

Chapter 13: Cron

What Is Cron?

• How Is Cron Executed?

Scheduling Cron Events

• Scheduling a Recurring Event
• Scheduling a Single Event
• Unscheduling an Event
• Specifying Your Own Cron Intervals
• Viewing Cron Events Scheduled

True Cron

Practical Use

• Deleting Post Revisions Weekly
• The Blog Pester Plugin
• The Delete Comments Plugin

Summary

Chapter 14: The Rewrite API

Why Rewrite URLs

• Permalinks Principles
• Apache’s mod_rewrite
• URL Rewriting in WordPress

How WordPress Handles Queries

• Overview of the Query Process
• The rewrite Object
• The query Object
• What Plugins Can Do

Practical Uses

• Rewriting a URL to Create a List of Shops
• Creating a New Permalink Structure and Integrating Non-WordPress Pages
• Adding an Endpoint and Altering Output Format
• Adding a Custom Feed for the Latest Uploaded Images

Summary

Chapter 15: Multisite

Differences

• WordPress Versus Multisite Network
• Understanding Multisite Terminology
• Advantages of Multisite

Enabling Multisite in WordPress

Multisite Functions

• The Power of Blog ID
• Common Functions
• Switching and Restoring Sites
• Network Content Shortcode Examples
• A Network Content Widget Example
• Creating a New Site
• Multisite Site Options
• Users in a Network
• Multisite Super Admin
• Checking the Site Owner
• Network Stats

Multisite Database Schema

• Multisite-Specific Tables
• Site-Specific Tables

Summary

Chapter 16: Debugging and Optimizing

Supporting Old Versions (Not)

• Keeping Current with WordPress Development
• Deprecated Functions
• Dealing with Obsolete Client Installs

Debugging

• Enabling Debugging
• Displaying Debug Messages
• Correcting Debug Messages

Error Logging

• Enabling Logging
• Setting Log File Location
• Understanding the Log File

Caching

• Saving, Loading, and Deleting Cached Data
• Caching Data Within a Plugin

Summary

Chapter 17: Marketing Your Plugin

Choosing a License for Your Plugin

• Different Options
• Why It Matters
• Making Money While Using the GPL

Submitting to WordPress.org

• Creating an Account
• Submitting a Plugin
• Setting Up SVN
• Creating a readme.txt File

Getting Your Plugin Renowned

• Naming Your Plugin
• Building a Web Site
• Creating a Page for Your Plugin
• Announcing Your Plugin
• Supporting Your Plugins
• Getting Feedback
• Getting Out of the Basement
• Other Promotion Methods

Summary

Chapter 18: The Developer Toolbox

Core as Reference

• Inline Documentation
• Finding Functions
• Common Core Files

Codex

• Searching the Codex
• Function Reference

Tool Web Sites

• PHPXref
• Hooks Database

Community Resources

• Support Forums
• Mailing Lists
• WordPress Chat
• WordPress Development Updates
• WordPress Ideas
• Community News Sites
• Local Events

Tools

• Browser
• Editor
• Deploying Files with FTP, SFTP, and SSH
• phpMyAdmin

Summary