The Who, What, Where, When, and Why of using WordPress Hooks. We will explore examples of rolling our own to allow other developers to hook into our code.

1. 5 W's of Hookin'
Nowell VanHoesen
@NowellVanHoesen
about.me/NowellVanHoesen

2. Hookin' Overview
What are Hooks
Who hooks
Why hook
Where are they
When to hook
Examples
@NowellVanHoesen5 W's of Hookin'

3. What are hooks?
A specific place/time in WordPress code
execution to add functionality or change data.
@NowellVanHoesen5 W's of Hookin'

4. What are hooks?
A specific place/time in WordPress code
execution to add functionality or change data.
Types:
– Action: add functionality at a specific point
when an event happens or is about to
happen.
@NowellVanHoesen5 W's of Hookin'

5. What are hooks?
A specific place/time in WordPress code
execution to add functionality or change data.
Types:
– Action: add functionality at a specific point
when an event happens or is about to
happen.
– Filter: modify data before some event
( save, display )
@NowellVanHoesen5 W's of Hookin'

6. Who hooks?
@NowellVanHoesen5 W's of Hookin'

7. Who hooks?
Any one who wants to add custom code to
change how WordPress behaves or modify
what is output to the browser.
@NowellVanHoesen5 W's of Hookin'

8. Who hooks?
Any one who wants to add custom code to
change how WordPress behaves or modify
what is output to the browser.
Anyone who wants to allow others to build on
to their plugin or theme.
@NowellVanHoesen5 W's of Hookin'

9. Why
@NowellVanHoesen5 W's of Hookin'

10. Why
use hooks
@NowellVanHoesen5 W's of Hookin'

11. Why
use hooks
● Tweak
functionality/output
to better fit your
needs
@NowellVanHoesen5 W's of Hookin'

12. Why
use hooks
● Tweak
functionality/output
to better fit your
needs
● Maintain your
customizations when
updating
@NowellVanHoesen5 W's of Hookin'

13. Why
use hooks
● Tweak
functionality/output
to better fit your
needs
● Maintain your
customizations when
updating
create hooks
@NowellVanHoesen5 W's of Hookin'

14. Why
use hooks
● Tweak
functionality/output
to better fit your
needs
● Maintain your
customizations when
updating
create hooks
● Allow others to add
functionality
@NowellVanHoesen5 W's of Hookin'

15. Why
use hooks
● Tweak
functionality/output
to better fit your
needs
● Maintain your
customizations when
updating
create hooks
● Allow others to add
functionality
● Allow others to filter
output from your
plugin/theme
@NowellVanHoesen5 W's of Hookin'

16. Where...
can I find them
@NowellVanHoesen5 W's of Hookin'

17. Where...
can I find them
● WordPress core
@NowellVanHoesen5 W's of Hookin'

18. Where...
can I find them
● WordPress core
● Themes
@NowellVanHoesen5 W's of Hookin'

19. Where...
can I find them
● WordPress core
● Themes
● Plugins
@NowellVanHoesen5 W's of Hookin'

20. Where...
can I find them
● WordPress core
● Themes
● Plugins
can I create them
@NowellVanHoesen5 W's of Hookin'

21. Where...
can I find them
● WordPress core
● Themes
● Plugins
can I create them
● Themes
@NowellVanHoesen5 W's of Hookin'

22. Where...
can I find them
● WordPress core
● Themes
● Plugins
can I create them
● Themes
● Plugins
@NowellVanHoesen5 W's of Hookin'

23. Where...
can I find them
● WordPress core
● Themes
● Plugins
can I create them
● Themes
● Plugins
● WordPress core
@NowellVanHoesen5 W's of Hookin'

24. Where...
can I find them
● WordPress core
● Themes
● Plugins
can I create them
● Themes
● Plugins
● WordPress core
@NowellVanHoesen5 W's of Hookin'

25. How?
Actions Filters
@NowellVanHoesen5 W's of Hookin'

26. How?
Actions
● add_action( t, f, p, a )
Filters
● add_filter( t, f, p, a )
@NowellVanHoesen5 W's of Hookin'
t = tag f = function p = priority a = # args

27. How?
Actions
● add_action( t, f, p, a )
● remove_action( t, f,
p, a )
Filters
● add_filter( t, f, p, a )
● remove_filter( t, f, p,
a )
@NowellVanHoesen5 W's of Hookin'
t = tag f = function p = priority a = # args

28. How?
Actions
● add_action( t, f, p, a )
● remove_action( t, f,
p, a )
● do_action( t, f, p, a )
Filters
● add_filter( t, f, p, a )
● remove_filter( t, f, p,
a )
● apply_filters( t, f, p,
a )
@NowellVanHoesen5 W's of Hookin'
t = tag f = function p = priority a = # args

29. How?
Actions
● add_action( t, f, p, a )
● remove_action( t, f,
p, a )
● do_action( t, f, p, a )
Filters
● add_filter( t, f, p, a )
● remove_filter( t, f, p,
a )
● apply_filters( t, f, p,
a )
@NowellVanHoesen5 W's of Hookin'
http://codex.wordpress.org/Plugin_API
t = tag f = function p = priority a = # args

30. Action hook example 1
// wp_enqueue_scripts action
add_action( 'wp_enqueue_scripts', 'nv_added_styles' );
function nv_added_styles() {
if ( !is_admin() ) {
wp_register_style(
'nv-ie-fix',
get_bloginfo( 'stylesheet_directory' ) . '/ie.css',
false
);
$GLOBALS['wp_styles']->add_data(
'nv-ie-fix',
'conditional',
'lte IE 8'
);
wp_enqueue_style( 'nv-ie-fix' );
}
}
@NowellVanHoesen5 W's of Hookin'

31. Action hook example 2
add_action( 'pre_get_posts', 'my_get_posts' );
function my_get_posts( $query ) {
global $wp_the_query;
if( $wp_the_query === $query && $query->is_home() ) {
add_filter( 'posts_where' , 'posts_where' );
$category_id = get_cat_ID( 'Scribblings' );
$query->set( 'cat', $category_id );
} else if ( is_archive() && is_date() && !is_category()) {
if ( !isset( $query->query_vars['post_type'] ) ) {
$query->set( 'post_type', array( 'post', 'myoldhouse', 'snapshots' ) );
$query->set( 'posts_per_page', -1 );
}
}
}
function posts_where( $where ) {
$where = " AND ( ( wp_term_relationships.term_taxonomy_id IN (1) AND wp_posts.post_type =
'post' ) OR ( wp_posts.post_type IN ('myoldhouse', 'snapshots') ) ) AND (wp_posts.post_status =
'publish' OR wp_posts.post_status = 'private')";
return $where;
}
@NowellVanHoesen5 W's of Hookin'

32. Filter hook examples
add_filter( 'the_title', 'nv_the_title', 10, 2 );
function nv_the_title( $title, $id ) {
if ( !is_admin() ) {
$title = 'WCCbus - ' . $title;
}
return $title;
}
// what core runs
return apply_filters( 'the_title', $title, $id );
add_filter( 'enter_title_here', 'change_default_post_title', 10, 2 );
function change_default_post_title( $text, $post ) {
if ( 'post' == get_post_type( $post ) ) {
return $text . “ - Required”;
}
}
@NowellVanHoesen5 W's of Hookin'

33. Time to go live...
@NowellVanHoesen5 W's of Hookin'

34. Time to go live...
@NowellVanHoesen5 W's of Hookin'

35. Resources
@NowellVanHoesen5 W's of Hookin'
Plugin API on the codex
- http://codex.wordpress.org/Plugin_API
Drew Jaynes – Filter of the Day: Three filters a day for 365
days
- http://fotd.werdswords.com/