Introduction to plugin development

@Josh412
Introduction To Plugin
Development
Josh Pollock | CalderaLabs.org

@Josh412
CalderaLabs.org
Hi I'm Josh
Lead Developer: CalderaWP
I make WordPress plugins
I teach about WordPress
I wrote a book about the WordPress REST API
I am core contributor to WordPress
I am a member of The WPCrowd

@Josh412
CalderaLabs.org
You Should Make Plugins

@Josh412
CalderaLabs.org
Turn Code Off
Easy troubleshooting!

@Josh412
CalderaLabs.org
Reuse Code
Share Between Projects

@Josh412
CalderaLabs.org
Share Code
Distribute on Github or WordPress.org

@Josh412
CalderaLabs.org
Make $$
Sell Plugins

@Josh412
CalderaLabs.org
What Is A Plugin?

@Josh412
How To Make A Plugin
Step 1: Add a new directory to the plugins directory
(optional).
Step 2: Add a file in that directory or the plugins
directory with a valid plugin header.
Step 3: Write code (optional).

@Josh412
CalderaLabs.org
Plugins Are
Containers For Code

@Josh412
CalderaLabs.org
Plugins vs Themes
Or Can’t I Put That In
functions.php ??

@Josh412
CalderaLabs.org
It’s a free software, you
can do whatever you
want, but...

@Josh412
Plugins vs Themes: Best Practices
Themes should be use to present a unique design
Everything else should be in a plugin.

@Josh412
Should This Code Go In functions.php ?
Is the answer to any of these questions no:
Do I ever want to reuse this code apart from this
theme?
Will I miss this code when I switch themes?
Switch for troubleshooting.
Switch for new look.
Can I use this code for other purposes?

@Josh412
CalderaLabs.org
Making Plugins
Organization

@Josh412
Plugin Header: Goes In Main File
<?php
/*
Plugin Name: My Plugin
*/

@Josh412
Main File: The File With A Plugin Header
Plugin Header
License/ Copyright/ Contact Info
Check Dependencies & Requirements
Load Plugin
Start Plugin

@Josh412
Directory Structure
There Are No Rules
You Should Have Rules
I like PSR-4 :)

@Josh412
Naming Things
There Are No Rules
You Should Have Rules
I like to document naming
conventions:)

@Josh412
Naming Things: naming-conventions.txt
Plugin Name --
Text domain --
Function prefix --
Class prefix --
Root namespace --
Hook Prefix --

@Josh412
CalderaLabs.org
Making Plugins
The Plugins API

@Josh412
CalderaLabs.org
Hooks Are Events
When We Get Here:
Do This

@Josh412
CalderaLabs.org
Don’t
Hack Core
Modifying Core/ Plugins / Themes Is A Bad Idea
You Will Lose Your Changes On Update

@Josh412
CalderaLabs.org
Hooks Let You Change
WordPress/ Plugins/
Themes
Without Editing Files

@Josh412
CalderaLabs.org
Filters
Change A Variable’s Value
At A Specific Time

@Josh412
CalderaLabs.org
Actions
Do Something
At A Specific Time

@Josh412
Actions
Do something
Don’t return values*
Actions Vs Filters
Filters
Change something
Must return a value*

@Josh412
CalderaLabs.org
Use Hooks In Your Plugins
To Add New Functionality

@Josh412
CalderaLabs.org
Add Hooks In Your Plugins
To Make Your Plugin
Extensible

@Josh412
do_action()
Triggers the action
Using Actions
add_action()
Hooks a function to an action

@Josh412
Using Actions: Print Tracking Pixel
function my_prefix_pixel() {
echo '<img src="https://adnetwork.com/pixel.gif"
width="0" height="0">';
}
add_action( 'wp_footer', 'my_prefix_pixel' );

@Josh412
Using Actions: Modify WP_Query
function search_filter($query) {
if ( !is_admin() && $query->is_main_query() ) {
if ($query->is_search) {
$query->set('post_type', array( 'post', 'movie' ) );
}
}
}
add_action('pre_get_posts','search_filter');

@Josh412
apply_filters()
Creates the filter
Using Filters
add_filter()
Hooks a function to a filter

@Josh412
Using Filters: Add To Content
add_filter( 'the_content', 'slug_callback' );
function slug_callback( $content ){
return $content . '<p class="cta">Hey Sign Up for My
Thing!</p>';
}

@Josh412
Using Filters: Add To Content
add_filter( 'the_content', function( $content ){
return $content . '<p class="cta">Hey Sign Up for
My Thing!</p>';
});

@Josh412
Creating Filters: Before
function prefix_get_form( $id ){
return get_option( $id, [] );
}

@Josh412
Creating Filters: After
function prefix_get_form( $id ){
$form = get_option( $id, [] );
$form = apply_filters( 'prefix_get_form', $form, $id );
return $form;
}

@Josh412
Hook Priority
add_filter( 'name','callback', 2 );
add_filter( 'name', 'callback_two', 55 );

@Josh412
Hook Arguments
$form = apply_filters( 'prefix_get_form', $form, $id );
add_filter( 'prefix_get_form', function( $form, $id ){
if( 'CF1234567' == $id ){
// do something to $form
}
return $form;
}, 10, 2 );

@Josh412
CalderaLabs.org
Making Plugins
Josh’s Rules For Plugin
Development

@Josh412
CalderaLabs.org
Security Is Not
Optional

@Josh412
CalderaLabs.org
Trust No Inputs

@Josh412
HTTP requests
That functions will be used how you intended
them
Data returned from the database
Yourself
Some Things Not To Trust

@Josh412
CalderaLabs.org
Write For Reuse

@Josh412
CalderaLabs.org
Use Version
Control

@Josh412
CalderaLabs.org
Commit Early
Commit Often

@Josh412
Single Responsibility Principle
Functions should do one thing.
Do Not Repeat Yourself (DRY)
Functions, not copypaste
Making Code Reusable

@Josh412
CalderaLabs.org
Abstraction!!

@Josh412
CalderaLabs.org
Using Classes
Doesn’t Make Your
Code
Object-Oriented

@Josh412
CalderaLabs.org
Use
Object-Oriented
Programming
When Appropriate

@Josh412
CalderaLabs.org
Small Simple
Classes Are Good

@Josh412
CalderaLabs.org
Josh Pollock
JoshPress.net
CalderaLabs.org
CalderaWP.com
IngotHQ.com
@Josh412

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