How Not to Build a WordPress Plugin

How Not to Build a WordPress Plugin
Will Norris < http://willnorris.com />

Upgradability
Performance
Security
Extensibility

Unique Function Names

Function Name Prefix
wcpdx_activate()
wcpdx_deactivate()
wcpdx_uninstall()

Class
class WordCampPDX {
function activate()
function deactivate()
function uninstall()
}

Never Assume File Location

Traditional Directory Layout
example.com/
wordpress/
wp-config.php
wp-content/
plugins/
themes/

Non-Traditional Layout (since WP 2.6)
example.com/
wordpress/
wp-config.php
wordpress-content/
plugins/
themes/

Plugin URL
ur doin it wrong:
<img src=”<?php bloginfo(‘wpurl’) ?>/wp-content/plugins/wcpdx/logo.png” ?>
dats bedder:
<img src=”<?php echo WP_PLUGIN_URL ?>/wcpdx/logo.png ?>”/>
you haz it:
<img src=”<?php echo plugins_url(‘logo.png’, __FILE__) ?>” />

Plugin URL
plugins_url()
supports WPMU plugin directory
auto detects SSL
supports renamed plugin directory
calls ‘plugins_url’ filter

Friends of plugins_url()
site_url()
admin_url()
includes_url()
content_url()
no home_url() (why not?)

Including Files
ur doin it wrong:
include ‘../../wp-content/...’
dats bedder:
include ABSPATH . ‘wp-content/...’
you haz it:
include WP_CONTENT_DIR . ‘/...’

Find the Right Hook
Load as late as possible, but no later

Admin Hooks
ur doin it wrong:
add_action(‘admin_init’, ‘wcpdx_admin_init’)
add_action(‘admin_head’, ‘wcpdx_admin_head’)
you haz it:
$hookname = add_options_page( ... )
add_action(“admin_load-$hookname”, ‘wcpdx_admin_init’)
add_action(“admin_head-$hookname”, ‘wcpdx_admin_head’)

Styles and Scripts
ur doin it wrong:
<script rel=”<?php echo plugins_url(‘wcpdx.js’, __FILE__) ?>”></script>
you haz it:
wp_enqueue_script(‘wcpdx’, plugins_url(‘wcpdx.js’, __FILE__))
wp_enqueue_style(‘wcpdx’, plugins_url(‘wcpdx.css’, __FILE__))

Styles and Scripts
wp_register_* and wp_enqueue_*
support dependencies
push scripts to footer
caching support based on version
(one day) server side concatenation

Add your own hooks
A strategically placed hook covers a multitude of sins.

Custom Hooks
Can do everything core WP hooks do:
event notification (actions)
massage data (the_content)
replace values (stylesheet)
extend functionality (http_api_curl)
replace functionality

Custom Hooks
do_action(‘my-action’)
do_action(‘my-action’, $a, $b)
do_action_ref_array(‘my-action’, array($wcpdx))
apply_filters(‘my-filter’, $wcpdx)
apply_filters(‘my-filter’, $wcpdx, $a, $b)

Custom Tables

Designed for Flexibility
WordPress database supports
custom options
arbitrary metadata for posts, users, and comments (2.9)
custom taxonomies
custom post types

Custom Post Types
Used by WordPress core for
posts
pages
revisions
attachments

If it walks like a duck...
author
date and time
title
content
comments
categories and tags
permalink
order
hierarchy
(additional arbitrary metadata)

Admin Settings Pages

Don’t waste time processing manually
register_setting( ‘wcpdx’, ‘my-option’ )
http://codex.wordpress.org/Settings_API
http://codex.wordpress.org/Creating_Options_Pages# Register_Settings

Do you really need a dedicated page?
Add options to any built-in settings page
add_settings_field( ... )

Direct Plugin Files

Direct Plugin File Calls
Direct HTTP request to plugin file ajax.php:
echo ‘<script type=”text/javascript”>
jQuery.get(“‘ . plugins_url(‘ajax.php’, __FILE__) . ‘”);
// do something with AJAX data
</script>’;

Direct Plugin File Calls
If ajax.php includes anything similar to:
require_once(‘../../../wp-load.php’);
ur doin it wrong

WordPress Requests
Permalink URL:
http://example.com/2009/01/hello-world
becomes:
http://example.com/index.php?
year=2009&
monthnum=01&
name=hello-world

Custom WP Request
Instead of making an AJAX call to:
http://example.com/wp-content/plugins/wcpdx/ajax.php
we want a URL like:
http://example.com/index.php?wcpdx=ajax-handler

Custom WP Requests
function wcpdx_parse_request($wp) {
// only process requests with "wcpdx=ajax-handler"
if (array_key_exists('wcpdx', $wp->query_vars)
&& $wp->query_vars['wcpdx'] == 'ajax-handler') {
// process the request.
}
}
add_action('parse_request', 'wcpdx_parse_request');
function wcpdx_query_vars($vars) {
$vars[] = 'wcpdx';
return $vars;
}
add_filter('query_vars', 'wcpdx_query_vars');

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How Not to Build a WordPress Plugin

by Will Norris

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