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Writing your first WordPress plugin
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Writing Your First WordPress Pluginor, What I wish someone had told me because it would have prevented me from banging my head on the desk a lot
Boone Gorges@[email protected]://teleogistic.net
Who am I? – early 2009o Instructional Technologist, Queens College, CUNY
o Philosopher
o Good HTML and CSS knowledge. Some scripting experience
o Moderately high awesomeness
Who am I? – early 2010o Developer, CUNY Academic Commons http://commons.gc.cuny.edu
o A zillion plugins in WP repo http://wordpress.org/extend/plugins/profile/boonebgorges
o Extreme awesomeness
1) The structure of WordPress
WordPress is modular
Separable pieces: classes, functions, template files
Serial: Everything happens in a certain order
WordPress is modular
Plugins:
New classes, functions, or template files that either replace or augment WP “core”
2) Plugin basics
Where do plugins live?
Ask yourself:
- Is my plugin specific to a theme?- wp-content/[theme-dir]/functions.php
- Should my plugin activate on all blogs? (MU only)- wp-content/mu-plugins/my-plugin.php
- Otherwise- wp-content/plugins/my-plugin/my-plugin.php
Let WP know you exist
<?php/*Plugin Name: Boone’s PluginPlugin URI: http://teleogistic.netDescription: This plugin will blow your mindAuthor: boonebgorgesVersion: 1.0Author URI: http://teleogistic.net*/
wp-content/plugins/boones-plugin/boones-plugin.php
See http://codex.wordpress.org/Writing_a_Plugin#File_Headers
3) Example: Shortcode
Shortcodes fill in for frequently-typed stuff
Say you typed your address a lot:
The WordPress Shortcode API
function address_shortcode() {return '<p>Boone Gorges<br />24 Gumdrop Lane<br />Apartment #32<br />Sugarlove, MD 20020</p>';
}add_shortcode( 'bgaddress', 'address_shortcode' );
wp-content/plugins/boones-plugin/boones-plugin.php
See http://codex.wordpress.org/Shortcode_API
Soup that baby up
function address_shortcode($atts) {extract(shortcode_atts(array(
'location' => 'MD'), $atts));
if ( $atts['location'] == 'MD' ) return '<p>Boone Gorges<br /> 24 Gumdrop Lane<br /> Apartment #32<br /> Sugarlove, MD 20020</p>';
else return '<p>Boone Gorges<br /> 85 Lollipop Street<br /> Apartment #81<br /> Milwaukee, WI 54112</p>';
}add_shortcode( 'bgaddress', 'address_shortcode' );
wp-content/plugins/boones-plugin/boones-plugin.php
See http://codex.wordpress.org/Shortcode_API
There's a Widgets API too
See http://codex.wordpress.org/Widgets_API
4) Example: Hooks
Actions are hooks
In the core:do_action( 'loop_start' );
In your plugin:add_action( 'loop_start', 'my_code' );
Example: A hello message
function well_hello_there() {global $user_identity;
if ( is_user_logged_in() )echo "Welcome, " . $user_identity;
elseecho "Welcome, anonymous lurker!";
} add_action( 'loop_start', 'well_hello_there' );
wp-content/plugins/boones-plugin/boones-plugin.php
See http://codex.wordpress.org/Plugin_API/Action_Reference
Filters are hooks…with benefits
In the core:$content = apply_filters('the_content', $content);
In your plugin:add_filter( 'the_content', 'my_code' );
Example: Makin' it 1337
function make_it_leet( $content ) {$leet_content = str_replace( 'e', '3', $content );return $leet_content;
} add_filter( 'the_content', 'make_it_leet' );
wp-content/plugins/boones-plugin/boones-plugin.php
See http://codex.wordpress.org/Plugin_API/Filter_Reference
5) The plugin dev's toolbox
The WordPress Codex, especially:- http://codex.wordpress.org/Shortcode_API - http://codex.wordpress.org/Widgets_API- http://codex.wordpress.org/Plugin_API
The WordPress PHP Cross-Reference- http://xref.yoast.com
The WordPress plugin repository:- http://wordpress.org/extend/plugins to download- http://wordpress.org/extend/plugins/about to add your own plugin
PHP resources- W3Schools – http://www.w3schools.com/PHP/- php.net – http://www.php.net/manual/en
Resources on the web
A good text editor, ideally one with- the ability to save over FTP- good search-and-replace- code highlighting- see http://lifehacker.com/385929/best-text-editors for suggestions
A local development environment- AMP: Apache, MySQL, PHP- Windows: XAMPP; Mac: MAMP- Use SVN to get the most recent copies of WordPress
Resources on your computer
The White Screen Of Death- Usually means you have a syntax error (check your punctuation!)- No duplicate function names, except for functions in pluggable.php- Use if ( function_exists( 'my_function' ) )
Get to know your data- Learn about globals: $wp, $post, $comment- var_dump( $wp );- print "<pre>"; print_r( $wp ); print "</pre>";- die();
Pick apart existing plugins
Ask for help: http://wordpress.org/support
Words of advice
