Code examples from my Asheville WordCamp 2016 talk entitled "Using Hooks (and creating your own)"

.WordPress-Using-hooks.php

<?php
/**
 * Attempting to register a post type within a plugin, without using a hook, 
 * results in a fatal error
 */
$args = array(
	... etc ...
);
register_post_type( 'my_post_type', $args );

/* OOPS! I broke everything!! */

_02-fatal-error-fixed-by-init-hook.php

<?php
/**
 * To fix the problem, we can wrap our call to `register_post_type` inside a function
 */
function my_register_post_type() {
	$args = array(
		... etc ...
	);
	register_post_type( 'my_post_type', $args );
}

/**
 * ...And then we can tell WP to run our function on the 'init' hook
 */
add_action( 'init', 'my_register_post_type' );

_03-enqueue-scripts.php

<?php
/**
 * Register/enqueue CSS and JS files on the front end
 *
 *		- Define a function that registers/enqueues our files
 *		- Tell WP to run our function at the correct time
 * 
 * @link	https://codex.wordpress.org/Plugin_API/Action_Reference/wp_enqueue_scripts
 */
function my_enqueue_scripts() {

	# enqueue a CSS file
	wp_enqueue_style( 'my-handle', 'filename.css' );
  
	# enqueue a JS file
	wp_enqueue_script( 'my-handle', 'filename.js' );
}
add_action( 'wp_enqueue_scripts', 'my_enqueue_scripts' );

_04-save-post.php

<?php
/**
 * Send an email upon saving a post with post type 'news_update'
 *
 * @param	int		$post_id	The post ID being saved
 * @param	WP_Post		$post		The post object being saved
 * @param	bool		$update		Whether this is a post being updated (as opposed to a new post being created)
 * 
 * @link 	https://codex.wordpress.org/Plugin_API/Action_Reference/save_post
 */
add_action( 'save_post', 'my_project_updated_send_email', 10, 3 );
function my_project_updated_send_email( $post_id, $post, $update ) {

	// If this is just a revision, don't send the email.
	if ( wp_is_post_revision( $post_id ) || wp_is_post_autosave( $post_id ) ) {
		return;
	}
	
	if( 'news_update' != $post->post_type ) {
		return;
	}

	$post_title = get_the_title( $post_id );
	$post_url = get_permalink( $post_id );

	/* ... etc ... */

	// Send email to admin.
	wp_mail( 'admin@example.com', $subject, $message );
}
add_action( 'save_post', 'my_project_updated_send_email' );

_05-post-row-actions.php

<?php
/**
 * Filter the post row actions on the edit.php screen
 *
 * @param 	array 		$actions 	The existing array of actions
 * @param 	WP_Post		$post 		The post whose row actions are being edited
 * @return 	array
 */
add_filter( 'post_row_actions', 'my_post_row_actions', 10, 2 );
function my_post_row_actions( $actions, $post ) {

	# don't do anything if we're viewing posts in the trash
	if( ! empty( $_GET['post_status'] ) && 'trash' == $_GET['post_status'] ) {
		return $actions;
	}

	/**
	 * Remove the "Trash" link
	 *
	 * (probably don't actually do this)
	 */
	if( isset( $actions['trash'] ) ) {

		unset( $actions['trash'] );
	}
	
	# URL needed here
	$actions['my_action'] = '<a href="'.'">My Action</a>';

	return $actions;

}

_06-plugin-action-links.php

<?php
/**
 * Remove the "Edit" link for this plugin
 *
 * @param 	array 	$links 		The current actions links
 * @return 	array
 */

$plugin = plugin_basename( __FILE__ );

add_filter( 'plugin_action_links_' . $plugin, 'my_plugin_links' );
function my_plugin_links( $links ) {

	# remove the "Edit" link
	if( array_key_exists( 'edit', $links ) ) {

		unset( $links['edit'] );
	}

	return $links;
}

_07-creating-filter-hook.php

<?php
/**
 * Creating our own filter hook
 */

# start with the number 4
$my_number = 4;

# let other people change the number
$my_number = apply_filters( 'edit_my_number', $my_number );

/**
 * Probably still equal to 4, unless someone is hooking into our
 * filter
 */
echo $my_number; 

_08-actually-using-filter-hook.php

<?php
/**
 * Actually using our own filter hook
 */

# subtract one from the number when it comes time
add_filter( 'edit_my_number', 'subtract_one' );
function subtract_one( $number ) {
	return $number - 1;
}

# start with the number 4
$my_number = 4;

# let other people change the number
$my_number = apply_filters( 'edit_my_number', $my_number );

/**
 * Now equal to 3 because we've hooked into the filter above
 */
echo $my_number; 

_09-using-filter-hook-multiple-times.php

<?php
/**
 * Using our filter hook multiple times
 */

# subtract one from the number
add_filter( 'edit_my_number', 'subtract_one', 10 );
function subtract_one( $number ) {
	return $number - 1;
}

# multiply the number by -3
add_filter( 'edit_my_number', 'times_negative_three', 9 );
function times_negative_three( $number ) {
	return $number * (-3);
}

# start with the number 4
$my_number = 4;

# let other people change the number
$my_number = apply_filters( 'edit_my_number', $my_number );

echo $my_number; // now equal to -13

_10-crazy-filter-hooks.php

<?php
/**
 * Getting crazy with our filter hook
 */

# start with the number 4
$my_number = 4;

# Equal to 0 or 1 depending on current timestamp
$wildcard_number = time() % 2;

# subtract one from the number, if the wildcard is === 0
add_filter( 'edit_my_number', 'maybe_subtract_one', 10, 2 );
function maybe_subtract_one( $number, $wildcard ) {

	if( 0 === $wildcard ) {

		return $number - 1;
	}

	return $number;
}

# let other people change the number
$my_number = apply_filters( 
	'edit_my_number', $my_number, $wildcard_number 
);

echo $my_number; // equal to either 3 or 4

_11-bbd-before-fields-wrap.php

<?php
/**
 * Hook into the area above the Big Boom Directory fields area and render some HTML
 * 
 * @link    https://wordpress.org/plugins/big-boom-directory
 */
add_action( 'bbd_before_fields_wrap', 'my_before_fields_wrap' );
function my_before_fields_wrap() {
?>
	<p><a href='#'>Share this listing</a></p>
<?php
}