These are the presentation slides from the WordPress GTA Meetup presentation Hooking with WordPress: WordPress Plugins 103 as used on November 19, 2012

1. Hooking with WordPress
WordPress Plugins 103

2. WordPress Hooks
WordPress Hooks
• Actions
• Filters

3. WordPress 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,
ACTION API.
USING THE
~~ WORDPRESS CODEX

4. WordPress Actions
WordPress Hooks
Actions
• http://codex.wordpress.org/Plugin_API/Action_Reference

5. WordPress Actions
Basic Functions
• do_action()
– http://codex.wordpress.org/Function_Reference/do_action
• add_action()
– http://codex.wordpress.org/Function_Reference/add_action
• remove_action()
– http://codex.wordpress.org/Function_Reference/remove_action

6. WordPress Actions
Basic Functions
• do_action()
– http://codex.wordpress.org/Function_Reference/do_action
This is where the action fires in the code,
and where your hook will attach itself.
Example: do_action( „my_action‟ );

7. WordPress Actions
Basic Functions
• add_action()
– http://codex.wordpress.org/Function_Reference/add_action
This is what you use to add your action (or
functionality) to the do_action() sequence.
Example:
add_action( „my_action‟, „my_functionality‟, 10 );

8. WordPress Actions
Basic Functions
• remove_action()
– http://codex.wordpress.org/Function_Reference/remove_action
This is what you use to remove a specific
action that has been added … and it
requires a call to an action, too?!

9. WordPress Actions
Basic Functions
• remove_action()
Example:
function remove_my_action(){
remove_action( „my_action‟, „my_functionality‟, 10 );
}
add_action( „init‟, „remove_my_action‟ );
Note: the priority being used; and, adding to
the init action.

10. WordPress Filters
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
ITSPHP FUNCTIONS IS EXECUTED TO MODIFY
SPECIFIC TYPES OF TEXT AT THESE TIMES,
USING THE FILTER API.
~~ WORDPRESS CODEX

11. WordPress Filters
WordPress Hooks
Filters
• http://codex.wordpress.org/Plugin_API/Filter_Reference

12. WordPress Filters
Basic Functions
• apply_filters
– http://codex.wordpress.org/Function_Reference/apply_filters
• add_filter
– http://codex.wordpress.org/Function_Reference/add_filter
• remove_filter
– http://codex.wordpress.org/Function_Reference/remove_filter

13. WordPress Filters
Basic Functions
• apply_filters
– http://codex.wordpress.org/Function_Reference/apply_filters
This is where the filter fires in the code, and
where your hook will attach itself.
Example:
apply_filters( „my_filter‟, „my_original_value‟ );

14. WordPress Filters
Basic Functions
• add_filter
– http://codex.wordpress.org/Function_Reference/add_filter
This is what you use to add your filter (or
new value) to the apply_filters() item.
Example:
add_filter( „my_filter‟, „my_new_value‟ );

15. WordPress Filters
Basic Functions
• remove_filter
– http://codex.wordpress.org/Function_Reference/remove_filter
This is what you use to remove a specific
filter that has been used … and it is best to
follow the remove_action() example as the
safest method to implement.

16. WordPress Filters
Basic functions
• remove_filter()
Example:
function remove_my_filter(){
remove_filter( „my_filter‟, „my_new_value‟, 20 );
}
add_action( „init‟, „remove_my_filter‟ );
Note: the priority being used; and, adding to
the init action.

17. Hooking with WordPress
1. Open your local test environment
2. Make sure the BNS Bio plugin is installed
and activated
3. Add the [bns_bio] shortcode to a post
4. Open your text editor
5. Navigate to the BNS Bio folder
6. Ready?

18. BNS Bio Plugin
The BNS Bio plugin adds a simple
shortcode to your WordPress installation
that outputs the author details of the post it
is added to.
The plugin uses a different approach to
options by utilizing “extension” plugins
versus an options panel. This is primarily for
the purposes of using BNS Bio as example
code.

19. BNS Bio Structures
• Uses the Class PHP structure
– Uses a simple constuctor method
• __construct()
– Enqueues its own stylesheet with an optional
call to a custom stylesheet
• Scripts_and_Styles()
– Collect the author details which it passes back
to the shortcode `bns_bio`
• author_block()

20. BNS Bio __construct()
The constructor method of the BNS Bio
class calls an action to add the
Scripts_and_Styles functionality …
/** Add Scripts and Styles */
add_action( 'wp_enqueue_scripts', array( $this, 'Scripts_and_Styles' ) );
… note the difference from the earlier
example.

21. WordPress Actions
Basic Functions
• add_action()
– http://codex.wordpress.org/Function_Reference/add_action
Example:
add_action( „my_action‟, „my_functionality‟, 10 );
Using in a Class example:
add_action( „my_action‟, array( $this, „my_functionality‟ ) );

22. BNS Bio author_block()
• This is the main code of the plugin.
• There are many instances of hooks
(actions and filters) available to work with.
Examples:
do_action( 'bns_bio_before_all' );
apply_filters( 'bns_bio_author_url_text', …
apply_filters( 'bns_bio_author_desc', …

23. BNS Bio Box
This is an “extension plugin” for BNS Bio.
It adds a rounded corner border, or box,
around the BNS Bio output by hooking an
additional CSS container into the
„bns_bio_before_all‟ and „bns_bio_after_all‟
actions; then adding the appropriate style
properties to create the look.

24. BNS Bio Box Code
The essentials:
• Define the functions to be used
• Hook them into the appropriate action
– add_action( 'bns_bio_before_all', 'bns_bio_open_box' );
– add_action( 'bns_bio_after_all', 'bns_bio_close_box' );
• Add the stylesheet (using the common
enqueue method; and another add_action
call)

25. BNS Bio List
This is another “extension plugin” for BNS
Bio that changes the output to an unordered
list by hooking into the available actions and
adding the appropriate HTML („ul‟ and „li‟)
elements.
It also includes its own enqueued stylesheet
and calls an optional custom stylesheet if
available.

26. BNS Bio List Code
The essentials:
• Add the „ul‟ container:
– add_action( 'bns_bio_before_all', function(){ echo '<ul class="bns-bio-list">'; }, 20 );
– add_action( 'bns_bio_after_all', function(){ echo '</ul><!-- .bns-bio-list -->'; }, 9 );
• Add the „li‟ containers:
– add_action( 'bns_bio_before_author_name', 'bns_bio_list_item' );
– add_action( 'bns_bio_before_author_url', 'bns_bio_list_item' );
– add_action( 'bns_bio_before_author_email', 'bns_bio_list_item' );
– add_action( 'bns_bio_before_author_desc', 'bns_bio_list_item' );
NB: I used two different methods for adding the
functionality: a call to a predefined function
(„bns_bio_list_item‟) and anonymous functions1

27. BNS Bio List Notes
1. The anonymous functions were used for
example purposes and may not work with
versions of PHP earlier than 5.3.0 where
they were introduced.

28. BNS Bio Hide
This is another “extension plugin” for BNS
Bio that changes the output by hiding the
author email details.
There are actually three items that need to
be addressed to hide the email line in the
output:
• What displays before the email
• What displays as the author (pre) email text
• What displays as the author email

29. WordPress Plugins 103
The essentials:
• remove_action( 'bns_bio_before_author_email', 'bns_bio_list_item' );
– (as applied to the init hook – see original „remove_action‟ example)
• add_filter( 'bns_bio_author_email_text', '__return_null', 100 );
• add_filter( 'bns_bio_author_email', '__return_null', 100 );
Notes:
• The remove_action priority is left as the default as the „bns_bio_list_item‟
function was added at the default priority (these priorities must match).
• Filters are essentially a “last one standing” mechanism; and in this case, the
WordPress „__return_null‟ function was called at a very late priority to help
insure it is last to run and therefore the final output.

30. WordPress Plugins 103
Hooking with WordPress
Questions and Answers

31. Credits
Presented by Edward Caissie
for the WordPress GTA Meetup group
on November 19, 2012.
Contact Details:
Email: edward.caissie@gmail.com
URL: http://edwardcaissie.com

32. Quick Resources
Codex References - Actions:
http://codex.wordpress.org/Plugin_API/Action_Reference
http://codex.wordpress.org/Function_Reference/do_action
http://codex.wordpress.org/Function_Reference/add_action
http://codex.wordpress.org/Function_Reference/remove_filter
Codex References – Filters:
http://codex.wordpress.org/Plugin_API/Filter_Reference
http://codex.wordpress.org/Function_Reference/apply_filters
http://codex.wordpress.org/Function_Reference/add_filter
http://codex.wordpress.org/Function_Reference/remove_filter

33. WordPress Power Point Template Credits
m62 visualcommunications:
http://www.m62.net/powerpoint-templates/technology-templates/wordpress-powerpoint-template/

34. WordPress Plugins 103: Hooking with WordPress
Thank You.