Develop Plugins Like a Pro

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Alison Barrett Senior Web Engineer at 10up @alisothegeek

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Agenda 1. Make a plugin 2. Actions & filters 3. Scripts & styles 4. Make a plugin 5. Custom queries 6. Widgets API 7. Make a plugin

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Not Covered ‣ PHP basics ‣ Version control ‣ Internationalization ‣ WordPress.org plugin submission

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You Should Have ‣ Local development environment ‣ IDE or text editor open to your plugins folder ‣ Browser open to the Plugins admin page

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First Plugin Hello WordPress

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Goals ‣ Show up on the Plugins page

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Actions and Filters

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Actions + Filters = Hooks

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"Hook" into WordPress core functionality

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action = do something ! ﬁlter = do something to something else

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function my_function() { … } add_action( 'init', 'my_function' );

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function my_other_function( $content ) { … return $content; } add_filter( 'the_content', 'my_other_function' );

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function append_author_bio( $content ) { $bio = get_the_author_meta( 'description' ); return $content . $bio; } add_filter( 'the_content', 'append_author_bio' );

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Scripts and Styles

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wp_head() fires the wp_head action

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function myplugin_scripts() { ?>

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‣ another plugin might load jQuery ‣ this might conflict with the WordPress version of jQuery ‣ that might not be where wp-content is

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never hardcode Javascript or CSS files in your plugin

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enqueue them instead

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action: wp_enqueue_scripts ! function: wp_enqueue_script wp_enqueue_style

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function myplugin_scripts() { wp_enqueue_script( 'jquery' ); wp_enqueue_script( 'myplugin', plugins_url( 'stuff.js', __FILE__ ) ); } add_action( 'wp_enqueue_scripts', 'myplugin_scripts' ); !

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function myplugin_scripts() { wp_enqueue_script( 'jquery' ); wp_enqueue_script( 'myplugin', plugins_url( 'stuff.js', __FILE__ ) ); ! wp_enqueue_style( 'myplugin', plugins_url( 'stuff.css', __FILE__ ) ); } add_action( 'wp_enqueue_scripts', 'myplugin_scripts' );

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plugins_url( 'myplugin.css', __FILE__ ); path within plugin file in plugin root

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wp_enqueue_script & wp_enqueue_style take 5 parameters

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wp_enqueue_script( 'myplugin', plugins_url( 'myplugin.js', __FILE__ ), array( 'jquery' ), '1.0.0', true ); unique ID URL to file dependencies version load in footer unique ID

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wp_enqueue_style( 'myplugin', plugins_url( 'myplugin.css', __FILE__ ), array(), '1.0.0', 'screen' ); unique ID URL to file dependencies version media

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Benefits of wp_enqueue_script ‣ Each file is only loaded once ‣ Dependencies are always loaded first and in the right order ‣ CSS files are called next to each other so they can load in parallel

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Second Plugin Authorial

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Goals ‣ Add an author bio to the end of every post ‣ Use the author bio field from the user's profile ‣ Show the author's Gravatar

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function authorial_enqueue_style() { wp_enqueue_style( 'authorial', plugins_url( 'authorial.css', __FILE__ ), array(), '1.0.0' ); } add_action( 'wp_enqueue_scripts', 'authorial_enqueue_style' );

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function authorial_add_bio( $content ) { $bio = get_the_author_meta( 'description' ); return $content . $bio; } add_filter( 'the_content', 'authorial_add_bio' );

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function authorial_add_bio( $content ) { $bio = wpautop( get_the_author_meta( 'description' ) ); return $content . $bio; } add_filter( 'the_content', 'authorial_add_bio' );

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Bonus Lesson: ! Output Buffering

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echo '

'; echo '

About the Author

'; echo $bio; echo '

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About the Author

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ob_start(); ?>

About the Author

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function authorial_add_bio( $content ) { $bio = wpautop( get_the_author_meta( 'description' ) ); ob_start(); ?>

About the Author

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$bio = wpautop( get_the_author_meta( 'description' ) ); $name = get_the_author_meta( 'display_name' ); ob_start();

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About

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Goals ✓ Add an author bio to the end of every post ✓ Use the author bio field from the user's profile ‣ Show the author's Gravatar

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$bio = wpautop( get_the_author_meta( 'description' ) ); $name = get_the_author_meta( 'display_name' ); $avatar = get_avatar( get_the_author_meta( 'ID' ), 100 ); ! ob_start();

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About

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.authorial-‐bio { padding: 20px; margin: 20px 0; overflow: hidden; background: #f5f5f5; border: 3px solid #e5e5e5; } ! .authorial-‐bio .avatar { float: left; margin: 20px 20px 10px 0; } ! .authorial-‐bio h3 { margin: 0; } ! .authorial-‐bio p { margin: 10px 0 0; } authorial.css

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Custom Queries

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The Loop

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query_posts

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query_posts( 'posts_per_page=3' ); query_posts( 'cat=13' ); query_posts( 'orderby=title&order=ASC' );

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WP_Query

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$my_query = new WP_Query( 'orderby=title&order=ASC' ); ! $my_query = new WP_Query( array( 'orderby' => 'title', 'order' => 'ASC', ) );

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if ( have_posts() ) : while ( have_posts() ) : the_post();

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if ( $my_query-‐>have_posts() ) : while ( $my_query-‐>have_posts() ) : $my_query-‐>the_post();

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Widgets API

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WP_Widget

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class My_Widget extends WP_Widget { ! public function __construct() { // widget name, ID, etc. } ! public function widget( $args, $instance ) { // outputs the content of the widget } ! public function form( $instance ) { // outputs the options form on admin } ! public function update( $new_instance, $old_instance ) { // processes widget options to be saved } ! }

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function __construct() { parent::__construct( 'my_widget', 'My Widget', array( 'description' => 'A Foo Widget', ) ); } unique ID title on Widgets page displays under title on Widgets page

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); ! echo $args['before_widget']; ! if ( ! empty( $title ) ) { echo $args['before_title'] . $title . $args['after_title']; } ! // Widget content here ! echo $args['after_widget']; } $args is set when the sidebar is registered $instance is data from the widget form in the admin

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public function form( $instance ) { if ( isset( $instance[ 'title' ] ) ) { $title = $instance[ 'title' ]; } else { $title = 'New title'; } ?>

Title:

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public function update( $new_instance, $old_instance ) { $instance = array(); $instance['title'] = strip_tags( $new_instance['title'] ); ! return $instance; }

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action: widgets_init ! function: register_widget

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function register_my_widget() { register_widget( 'My_Widget' ); } add_action( 'widgets_init', 'register_my_widget' ); class name

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Third Plugin Hot Topics

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Goals ‣ Add a widget that lists popular posts ‣ Use comment count to determine popularity ‣ Allow user to change the number of posts listed ‣ Allow user to choose whether to display comment count

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function hot_topics_register_widget() { require_once __DIR__ . '/class-‐hot-‐topics-‐widget.php'; register_widget( 'Hot_Topics_Widget' ); } add_action( 'widgets_init', 'hot_topics_register_widget' );

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class Hot_Topics_Widget extends WP_Widget { ! } class-hot-topics-widget.php

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public function __construct() { parent::__construct( 'hot_topics', 'Hot Topics', array( 'description' => 'A list of your most discussed posts', ) ); }

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); ! echo $args['before_widget']; ! if ( ! empty( $title ) ) echo $args['before_title'] . $title . $args['after_title']; ! echo $args['after_widget']; }

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); $hot_topics_query = new WP_Query( array( 'orderby' => 'comment_count', ! ) ); echo $args['before_widget']; ! if ( ! empty( $title ) ) echo $args['before_title'] . $title . $args['after_title']; ! echo $args['after_widget']; }

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); $hot_topics_query = new WP_Query( array( 'orderby' => 'comment_count', 'ignore_sticky_posts' => true, ) ); echo $args['before_widget']; ! if ( ! empty( $title ) ) echo $args['before_title'] . $title . $args['after_title']; ! echo $args['after_widget']; }

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); $hot_topics_query = new WP_Query( array( 'orderby' => 'comment_count', 'ignore_sticky_posts' => true, ) ); if ( $hot_topics_query-‐>have_posts() ) : echo $args['before_widget']; ! if ( ! empty( $title ) ) echo $args['before_title'] . $title . $args['after_title']; ! echo $args['after_widget']; endif; }

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if ( $hot_topics_query-‐>have_posts() ) : echo $args['before_widget']; ! if ( ! empty( $title ) ) echo $args['before_title'] . $title . $args['after_title']; ! echo '

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public function form( $instance ) { if ( isset( $instance[ 'title' ] ) ) { $title = $instance[ 'title' ]; } else { $title = 'Hot Topics'; } ?>

Title:

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public function update( $new_instance, $old_instance ) { $instance = array(); $instance['title'] = strip_tags( $new_instance['title'] ); ! return $instance; }

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Goals ✓ Add a widget that lists popular posts ✓ Use comment count to determine popularity ‣ Allow user to change the number of posts listed

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if ( isset( $instance[ 'title' ] ) ) { $title = $instance[ 'title' ]; } else { $title = 'Hot Topics'; } ! if ( isset( $instance['number_of_posts'] ) ) { $number_of_posts = (int) $instance['number_of_posts']; } else { $number_of_posts = 5; } form()

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Title:

Number of posts to show:

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public function widget( $args, $instance ) { $title = apply_filters( 'widget_title', $instance['title'] ); $number_of_posts = (int) $instance['number_of_posts']; ! $hot_topics_query = new WP_Query( array( 'orderby' => 'comment_count', 'ignore_sticky_posts' => true, 'posts_per_page' => $number_of_posts, ) );

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Goals ✓ Add a widget that lists popular posts ✓ Use comment count to determine popularity ✓ Allow user to change the number of posts listed ‣ Allow user to choose whether to display comment count

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Number of posts to show:

/> Display comment count?

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public function update( $new_instance, $old_instance ) { $instance = array(); $instance['title'] = strip_tags( $new_instance['title'] ); ! if ( ! empty( $new_instance['number_of_posts'] ) ) { $instance['number_of_posts'] = (int) $new_instance['number_of_posts']; } else { $instance['number_of_posts'] = 5; } ! if ( ! empty( $new_instance['show_comment_count'] ) ) { $instance['show_comment_count'] = true; } else { $instance['show_comment_count'] = false; } ! return $instance; }

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if ( $hot_topics_query-‐>have_posts() ) : if ( ! empty( $instance['show_comment_count'] ) ) { $show_comment_count = true; } else { $show_comment_count = false; } ! echo $args['before_widget']; widget()