My presentation from WordPress DC 11/9/10

1. WordPress Plugin Development for Beginners
John P. Bloch
Senior Web Developer
Avendi Media, Inc.
http://www.johnpbloch.com/
@johnpbloch

2. What Are Plugins?
 The stupid answer:
 Anything you want*
 *theoretically, at least
 The useful answer:
 Non-essential and elective aspects of any given
WordPress installation

3. Wait a Minute...
Aren't plugins just
extensions of
WordPress? Don't
they just add
functionality that isn't
there?

4. Plugins are Part of WordPress
 Plugins have primacy of place
 Plugins interact with WordPress in the same
way WordPress interacts with itself

5. An Example Plugin

6. How Do Plugins Work?
 Almost all plugin use hooks. There are two
kinds of hooks:
 Actions
 Filters
 What's the difference?
 Filters expect you to return something, and...
 … that's it!
 Hooks let you tell WordPress to execute a
function when the specified hook fires

7. How To Use Hooks
 Filters:
 <?php add_filter( 'filter_name', 'function_name' ); ?>
 Actions:
 <?php add_action( 'action_name', 'func_name' ); ?>
 Both functions take two optional arguments:
 Priority
 Accepted Arguments

8. How To Fire Hooks
 To fire an action:
 <?php do_action( 'action_name' ); ?>
 This fires all functions hooked into that action
 To fire a filter:
 <?php apply_filters( 'filter_name', 'Filter value' ); ?>
 The 'Filter value' will be the first argument of each
hooked function
 apply_filters will return the filtered input

9. How Does Priority Work?
Actions and filters are
executed in the order
they are added. So
this code will echo:
First
Second
Third

10. How Does Priority Work?
Priority changes this
order. Actions and
filters have a default
priority of 10. Using a
lower number gives it
higher priority. This
code ouputs:
Third
First
Second

11. Accepted Arguments
 Accepted arguments allows you to specify how
many arguments to send to a hooked function
 Defaults to 1 for both actions and filters
 The following would output:
Don't mention Joomla
Don't mention

12. Some Common Hooks
 Actions
 init
 template_redirect
 admin_init
 after_setup_theme
 wp_loaded
 wp_head
 wp_footer
 admin_menu
 Filters
 the_content
 the_title
 wp_title
 template_include
 body_class
 post_class

13. But Wait! There's More!
 One more way to hook into WordPress is
through shortcodes
 Shortcodes are inserted into a post or page
from the editor; WordPress replaces the
shortcode tags with dynamically generated
content
 Shortcodes are kind of like HTML:
 [foo bar='bar']
 [foo bar='bar']Some Content[/foo]

14. How to Add a Shortcode
 Shortcodes must be registered:
 <?php add_shortcode( 'tag_name', 'function_name' ); ?>
 Shortcode handlers take two optional
arguments:
 Arguments: an array of arguments from the
shortcode
 Content: the content (if any) of the shortcode
 Shortcode handlers should return, not echo,
their content

15. An Example of a Shortcode

16. Developer Toolbox
 Local development environment
 LAMPP Stack (XAMPP – http://apachefriends.org)
 Subversion
 Windows: TortoiseSVN or Cygwin
 Everything else: CLI
 Text Editor
 FTP client
 Mac: Transmit
 SSH Client
 Windows: Putty
 Reference
 PHPXref (http://www.phpxref.com)

17. WordPress Developer Toolbox
 Official Support Channels
 WordPress Codex (http://codex.wordpress.org/)
 WordPress Forums (http://wordpress.org/support/)
 IRC Channel #wordpress (chat.freenode.net)
 Mailing Lists (sort of) (http://codex.wordpress.org/Mailing_Lists)
 Unofficial Support Channels
 WordPress Answers (http://wordpress.stackexchange.com/)
 WordPress Docs (http://wpdocs.labs.thedextrousweb.com/)
 Alot of Books

18. Just Because

19. Adding Your Plugin to the Directory
 http://wordpress.org/extend/plugins/add/
 Answer a few questions
 Name – Very important! This will determine the
name of the directory your plugin creates
 Description
 Plugin URL (optional)
 … And wait!

20. What is SVN?
SVN, or Subversion, is a version control program.
Others include Git and Mercurial. Subversion is
used for core WordPress development/distribution
and official plugin development/distribution.
Once you have your repository, anybody in the
world can check it out. Only you* can check files
into it.
*Technically, Nacin and some others have global plugin repo commit
access. #blamenacin

21. How to Use SVN
 If you are on windows and use TortoiseSVN,
just follow these next steps substituting ”Click X
menu item” for ”Execute X command”
 Go to the directory into which you'd like the
repo to go:
 ~$ cd Documents/svn
 Check out your repository for the first time:
 ~$ svn co http://plugins.svn.wordpress.org/custom-post-permalinks/ custom-post-permalinks
 Edit to your heart's content

22. How to Use SVN
 When you're done making changes (or reach a
good stopping point), commit your changes:
 ~$ svn ci -m 'This is a description of the commit!'
 … Tada!

23. Some Other Notes on SVN
 Updating your plugin
 Tagging vs. Stable Trunk
 Branching
 Adding committers (and other admin tools)

24. Further Reading
 Core.
 Core.
 Core.
 Seriously. Just read core's runtime execution.
 Line by line.

25. Now Let's Get Down to Business!
Time to switch gears, open VIM,
and write a plugin!