This document discusses extending WordPress through plugins. It advises not to hack the WordPress core files and instead use plugins to add new functionality. Plugins can use hooks called actions and filters to modify WordPress behavior at certain points. Actions allow plugins to execute functions at specific times, while filters allow modifying text before it is saved or output. The document provides examples of actions and filters and best practices for plugin development like using unique names and coding standards. It also briefly introduces the Transient API and WP Events.

2. Extending WP
PART 2
Extending WordPress

3. Extending WP
CORE

4. Extending WP
core = essential WordPress files

5. Extending WP
DON’T

6. Extending WP
HACK

7. Extending WP
CORE

8. Extending WP
Don’t Hack Core
WHY?
Can’t Upgrade :(

9. Extending WP
Don’t Hack Core

10. Extending WP
PLUGINS

11. Extending WP
Plugins
“Plugins are tools to extend the
functionality of WordPress. The core of
WordPress is designed to be lean, to
maximize flexibility and minimize code
bloat. Plugins offer custom functions
and features so that each user can tailor
their site to their specific needs.”

12. Extending WP
Hello World

13. Extending WP
Hello World

14. Extending WP
Hello World

15. Extending WP
Hello World

16. Extending WP
Hello World

17. Extending WP
PROGRAMMING
YOUR
PLUGIN

18. Extending WP
HOOKS

19. Extending WP
TWO Actions
TYPES Filters

20. Extending WP
modify the default behavior of WP

21. Extending WP
Actions
“Actions are the hooks that the WordPress
core launches at specific points during
execution, or when specific events occur.
Your plugin can specify that one or more of
its PHP functions are executed at these
points, using the Action API.”

22. Extending WP
Actions
hook_name = name of action hook
your_function_name = name of function you have defined
to be executed following the specified action hook
priority (optional) = an integer that can be used to specify
the order of action hooks. (default: 10)
accepted_args (optional) = how many arguments your
function takes

23. Extending WP
Actions

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Actions

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Actions
http://codex.wordpress.org/Plugin_API/Action_Reference
plugins_loaded, wp_head, wp_print_styles,
wp_print_scripts, wp_footer,
wp_print_footer_scripts, add_attachment,
add_category, delete_category,
delete_post, edit_attachment,
edit_category, edit_post, publish_page,
publish_post, save_post, comment_post,
edit_comment, delete_comment

26. Filters
Extending WP
“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. Your plugin can
specify that one or more of its PHP
functions is executed to modify specific
types of text at these times, using the Filter
API.”

27. Extending WP
Filters
tag = name of filter hook
your_function_name = name of function you have defined
to be apply filter
priority (optional) = an integer that can be used to specify
the order of filter hooks. (default: 10)
accepted_args (optional) = how many arguments your
function takes

28. Filters
Extending WP

29. Extending WP
Filters
http://codex.wordpress.org/Plugin_API/Filter_Reference
wp_title, the_title, the_excerpt, the_content,
the_author, login_headertitle,
login_headerurl, login_message,
comment_excerpt, widget_title,
excerpt_length, excerpt_more

30. Extending WP
From WP.org...
Follow Coding Standards.
Use Unique Names.
Don’t hardcode DB prefixes but use $wpdb->prefix
instead. (ie. wp_)
SELECT only what you need.
Add define('WP_DEBUG', true); to your wp-config.php
file.

31. Extending WP

32. Extending WP
Adding Scripts (jQuery, etc.)

33. Extending WP
The “Wrong” Way

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35. Extending WP
The Right Way

36. Extending WP

37. Extending WP

38. Extending WP

39. Extending WP
Real Example

40. Extending WP
2 Other Really
Cool Things

41. Extending WP
Transient API
&
WP Events (Cron)

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Transient API

43. Extending WP
WP Events

44. Extending WP
Also check out WP Object Cache and plugin
caching solutions like WP Super Cache and W3
Total Cache.

45. ANY ?’s