An Introduction to WordPress Hooks. Presented by Andrew Marks at the Brisbane Northside WordPress Meetup on 21st March 2018.

1. An Introduction to Hooks

2. An exploration into everyone’s favourite
useless WordPress plugin - Hello Dolly

3. “This sounds like it might be useful!”

4. “…huh?”

5. “…huh?”
• WordPress ships with a simple plugin named
“Hello Dolly”
• Its name is a whimsical take on the
programmer's obligatory “Hello, World!”
• It’s trotted out only for pedantic programming
explanations like the one that you’re about to sit
through…

7. “Wow, that’s really useful!” said no one ever…

8. The Code

9. “…huh?”

13. WordPress Hooks
• A “hook” is a WordPress Event
• Hooks are provided by WordPress to allow
your plugin to “hook into” the rest of
WordPress; that is, to call functions in your
plugin at specific times, and thereby set your
plugin in motion.

16. WordPress Hooks
• As a WordPress post is loaded, each hook is
run in a specific order
• There are two types of hooks:
• Actions – adds functionality
• Filters – changes functionality

17. WordPress Actions
We just saw two “Actions” in action:
• add_action( 'admin_notices', 'hello_dolly' );
• add_action( 'admin_head', 'dolly_css' );

18. WordPress Actions
Let’s replace this:
• add_action( 'admin_notices', 'hello_dolly' );
With this:
• add_action( 'admin_footer', 'hello_dolly' );

19. WordPress Actions
What if we ran them together?
• add_action( 'admin_notices', 'hello_dolly' );
• add_action( 'admin_footer', 'hello_dolly' );
Would the output be the same?

20. WordPress Filters
Let’s replace this:
• add_action( 'admin_notices', 'hello_dolly' );
With this:
• add_filter( ’the_content', 'hello_dolly' );

21. WordPress Filters

22. WordPress Filters
Let’s edit the hello_dolly() function so it accepts
an input, and returns the input plus the lyric:
function hello_dolly($input) {
$chosen = hello_dolly_get_lyric();
return $input . "<p id='dolly'>$chosen</p>”;
}

23. WordPress Filters

24. Real World Examples
Register a Custom Menu in the Admin
function register_my_custom_menu_page() {
add_menu_page( 'custom menu title', 'custom menu',
'manage_options', 'myplugin/myplugin-admin.php', '', 'dashicons-admin-
site', 6 );
}
add_action( 'admin_menu', 'register_my_custom_menu_page' );

25. Real World Examples
Hook into Post Publishing
function publish_post_tweet($post_ID) {
global $post;
// Code to send a tweet with post info
}
add_action('publish_post', 'publish_post_tweet');

26. Real World Examples
Hook Into Widget Initialization
function create_my_widget() {
register_sidebar(array(
'name' => __( 'My Sidebar', 'mytheme' ),
'id' => 'my_sidebar',
'description' => __( 'The one and only', 'mytheme' ),
));
}
add_action( 'widgets_init', 'create_my_widget' );

27. Real World Examples
Hook Into Front-end Scripts and Styles
function theme_styles() {
wp_enqueue_style( 'bootstrap_css', get_template_directory_uri() . '/css/bootstrap.min.css' );
wp_enqueue_style( 'main_css', get_template_directory_uri() . '/style.css' );
wp_enqueue_script( 'bootstrap_js', get_template_directory_uri() . '/js/bootstrap.min.js',
array('jquery'), '', true );
wp_enqueue_script( 'theme_js', get_template_directory_uri() . '/js/theme.js', array('jquery',
'bootstrap_js'), '', true );
}
add_action( 'wp_enqueue_scripts', 'theme_styles' );

28. WordPress Wishlist?
Have you ever thought to yourself “This WordPress
thing is pretty good, but it would be amazing if it
did ‘x’…”