<Head> Presentation: Plugging Into Wordpress

Plugging into
Matt Harris

<head> conference
26th October 2008

1

Types of Wordpress Wordpress.com
Hosted blogging solution

Wordpress.org
Downloadable edition for use on your own server

Wordpress MU
Multi-user edition of Wordpress.org

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Hosted
Wordpress.com

Free

Maintained and backed up for you

Not hackable or pluggable by you

3
Hosted: scalable, Automa1c deals with the spikes you may
get

Customisable
Wordpress.org

Self-hosted

Complete code control

Maintenance, backup and reliability are
your responsibility

4
Customisable: hackable, expandable. Add your own
features

All of Wordpress.org pros and cons
Wordpress MU

Hosting of multiple blogs under one install

Bespoke permission settings per blog

Your own Wordpress.com

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Basically this is the meat behind Wordpress.com
Great for Uni’s, EducaEonal places, newspapers, blog networks etc

Hooks and
Filters

add_action($tag, $function, $priority, $accepted_args)

add_filter($tag, $function, $priority, $accepted_args)

add_shortcode($tag, $function)

http://www.flickr.com/photos/gaetanlee/2906941718/
13
Don’t hack at the core code – makes it difficult to update the your installaEon
Use hooks and filters to ‘inject’ an event into the page processing

Filters are the hooks that WordPress launches to modify text of various types before adding it to the database or sending it to the browser screen

Hooks aOach custom funcEons onto specific acEons
hOp://codex.wordpress.org/Plugin_API/AcEon_Reference
hOp://codex.wordpress.org/Plugin_API/Filter_Reference
hOp://codex.wordpress.org/Shortcode_API

Where to put your code

Plugins
Inside it’s own file

Theme folder in the file
functions.php

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Plugins advantage – easily switch off and onable
FuncEons – will always run – best if required as part of your theme (not covered today but example would be to change something a theme relies on – maybe the movement of a login buOon)

Simple Filter
<?php

function changeWord($content) {
$search = “wordpress”;
$replace = “my blog”;
return str_ireplace($search, $replace, $content);
}

add_filter(‘the_content’, ‘changeWord’);

?>

http://codex.wordpress.org/Plugin_API/Filter_Reference

15
‘the_content” is a built in Wordpress tag
Str_ireplace is case insensiEve

To test this included it in funcEons.php

Simple Filter
<?php

function changeWord($content) {
$search = “wordpress”;
$replace = “my blog”;
return str_ireplace($search, $replace, $content);
}

add_filter(‘the_content’, ‘changeWord’);

?>

http://codex.wordpress.org/Plugin_API/Filter_Reference

16
‘the_content” is a built in Wordpress tag
Str_ireplace is case insensiEve

To test this included it in funcEons.php

Simple Filter

Before After

17

Simple Hook
<?php

function addText() {
echo “Can you see me?”;
}

add_action(’wp_footer', ’addText’);

?>

http://codex.wordpress.org/Plugin_API/Action_Reference

18
wp_footer Runs when the template calls the wp_footer funcEon, generally near the boOom of the blog page.

Simple Hook
<?php

}


?>


19

Simple Hook
<?php

function changeTextCol() {
echo “
<style type=‘text/css’>
body { color: #0ff00f; }
</style>
“;
}

add_action(’wp_head', ’changeTextCol’);

?>


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Simple Hook

Before After

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Simple Shortcode
<?php

function myH1_shortcode($atts, $content = null) {
extract($atts);
return ‘
<div class=“heading”>
<h1 style=“color:’ . $colour . ‘”>' .
$content . '</h1>
</div>’;
}

add_shortcode(’heading', 'myH1_shortcode');

?>

http://codex.wordpress.org/Shortcode_API

22
Shortcodes cannot be nested be default. Must add do_shortcode($content) into your handler to do this

Since WP2.5 (fixed 2.5.1. parsing order)

Note this isn’t really safe, $content should be saniEzed first using (stripslashes(wp_filter_post_kses($content) and colour should be protected with aOribute_escape($colour)

Simple Shortcode
<?php

[heading color=“#f00”]This is my heading[/heading]

?>

Output

<div class=quot;headingquot;>
<h1 style=quot;color:#f00quot;>This is my heading</h1>
</div>

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Shortcodes cannot be nested be default. Must add do_shortcode($content) into your handler to do this

Namespacing

http://www.ﬂickr.com/photos/thost/2244046981/
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Namespacing
<?php

}


?>

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Namespacing
<?php

function tmh_addText() {
}

add_action(’wp_footer', ’tmh_addText’);

?>

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Plugin Code Structure
<?php

/*
Plugin Name: My Widget
Plugin URI: http://themattharris.com
Description: A widget that puts some text in the
sidebar
Author: Matt Harris
Version: 1.0
Author URI: http://themattharris.com
*/

?>

28

Widget Code Structure
<?php

function tmh_renderWidget($args) {
extract($args);
?>
<?php echo $before_widget; ?>
<?php echo $before_title .
wptexturize(’My Widget') .
$after_title;
?>
<p>My Widget Code</p>
<?php echo $after_widget; ?>
<?php
}

?>

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<?php

extract($args);
?>
$after_title;
?>
<?php
}

?>

30

<?php

extract($args);
?>
$after_title;
?>
<?php
}

?>

31

<?php

extract($args);
?>
wptexturize(‘My Widget’) .
$after_title;
?>
<?php
}

?>

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wp_specialchars ‐ Like htmlspecialchars except don't double‐encode HTML
enEEes

<?php

extract($args);
?>
$after_title;
?>
<?php
}

?>

33

Widget Registration Code
<?php

function tmh_widgetInit() {
if (function_exists('register_sidebar_widget’)) {
register_sidebar_widget('My Widget',
'tmh_renderWidget');
}
}

add_action( 'widgets_init', 'tmh_widgetInit');

?>

34

Putting it all together
<?php
/*
Plugin Name: My Widget
Plugin URI: http://themattharris.com
Description: A widget that puts some text in the sidebar
Author: Matt Harris
Version: 1.0
Author URI: http://themattharris.com
*/

extract($args);
?>

<?php echo $before_title . wptexturize('My Widget') . $after_title; ?>



<?php
}

function tmh_widgetInit() {
if ( function_exists('register_sidebar_widget') ) {
register_sidebar_widget('My Widget', 'tmh_renderWidget');
}
}

add_action( 'widgets_init', 'tmh_widgetInit');

?>

35

Protecting your blog

check_admin_referer($action, [$query_arg]);

Use with

wp_create_nonce($action);

Use this on any forms you have.

42


attribute_escape($text); // also tag escape

wp_filter_post_kses($data); // adds slashes

wp_filter_nohtml_kses($data); // adds slashes

Use these when outputting data

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aOribute_escape (used for escaping for HTML aOributes)
Kses checks for allow html (or removes it in nohtml)

<?php current_user_can($capability) ?>

Example
<?php
if (current_user_can(‘unfiltered_html’)) {
$data = Wp_filter_post_kses($data);
} else {
$data = wp_filter_nohtml_kses($data);
}
?>

http://codex.wordpress.org/Roles_and_Capabilities

44
aOribute_escape (used for escaping for HTML aOributes)
Kses checks for allow html (or removes it in nohtml)

Translation friendly

<?php __($message, $domain); ?>

<?php _e($message, $domain); ?>

Example
<?php _e(“Title:”,’tmh_pluginname’); ?>

http://codex.wordpress.org/Translating_WordPress

45
WP uses GNU geOext localizaEon framework
Message level translaEon

_e echos
__ doesn’t
Too much info to go into here on how to have wordpress do the translaEon, but its worth building this in from the start
$message is output/returned if no translaEon is found so always worth building this in

Help and More Information
Wordpress Mailing Lists
http://codex.wordpress.org/Mailing_Lists

Wordpress Codex (or Google term + “codex”)
http://codex.wordpress.org/

Wordpress Support Forum
http://wordpress.org/support/

Writing a Plugin
http://codex.wordpress.org/Writing_a_Plugin

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Wordpres support forum – if the FAQ can’t help
Google search – whole community out there that can help

Matt Harris
http://themattharris.com
me@themattharris.com

All the links:
http://ma.gnolia.com/people/themattharris/tags/plugging
%20into%20wordpress

Image credits:
“Hello … my name is”: http://www.ﬂickr.com/photos/thost/2244046981/
“Hooks for hand”: http://www.ﬂickr.com/photos/gaetanlee/2906941718/
“Wordpress Logo”: http://wordpress.org/about/logos/

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<Head> Presentation: Plugging Into Wordpress