Many developers know how to write code in php but that doesn't mean they can write code for Wordpress. When developing sites for clients in Wordpress, it sometimes preferably to write a custom function that will simplify data input, management and display. The Wordpress coding framework is continually evolving and provides a number of hooks (through actions & filters) to allow developers to quickly and easily grab functions to create world class websites. Charly will speak about the power of hooks and filters and explain some of the most common ones to use if you want to write your own custom functions, to make the management of your wordpress websites a breeze.

1. Stop Hacking Wordpress
Start Working With It!
Charly Leetham
www.AskCharlyLeetham.com

2. Share This...
@charlyjl
charlyleetham

3. What will we cover
• What is the Wordpress API
• What are Filters, Actions & Hooks
• Creating & Calling Actions
• Actions Example
• Creating & Applying Filters
• Filters Example
• Useful Resources

4. The API...
• Wordpress API is designed for anyone to
extend the base WP Functionality
• Create Plugins or Themes
• Integrate with 3rd Party Apps – data in / out
• Covers all the functions available to us
• Today, looking at a small part of the API,
Filters & Actions...
Generically known as Hooks...

5. Filters...
• Modify content.... That’s it!
• For example:
– Change post / page content
– Change widget titles
– RSS Feeds
– Image details
• Used by plugins to allow content to be
modified without changing core code

6. Actions
• Do something ... when called...
• Allow the ‘execution’ of functions at fixed
points in the code
• For example
– After Login
– After Logout
– When a widget is displayed
– When the theme is setup...

7. • Filters & Actions are basically the same
thing...
• Both use functions that are ‘hooked’ into
the WP core functions
• Functions we write can use / provide
actions and filters as well!

8. Calling Actions...
• Actions are called using do_action ie:
do_action (‘mypluginactions’,$var1,$var2);
This simply “tells” wordpress to find all functions
that are ‘hooked’ to this action and run them.
It also specifies any arguments that may be
passed to the function – in this case two: $var1,
$var2 – or there may be none.

9. Anatomy of an Action
• Hooking the action is done using
add_action($tag,$function,$priority,$args)
$tag – is the action you want to ‘hook to’
$function – the function you want to ‘hook’.
$priority – the order. 10 is default, 1 is the
highest.
$args – the number of arguments to pass to
the action

10. Adding Actions
<?php
function myfunction($var1=null, $var2=null) {
echo $var1.’<br>’;
echo $var2,’<br>’;
}
add_action(‘mypluginactions’,’myfunction’,10,2);
?>
This will run ‘myfunction’, when the action
‘mypluginactions’ is called and pass 2 arguments.

11. Actions: Some Uses
• Loading Scripts & StyleSheets
• Recording user access (login & logout)
• Building Child Themes
– Adding / removing functionality
• Author Bio on posts
• “Share This”
• Adding / Saving Meta Data for Posts
• Processing Ajax Requests

12. Hooking filters
• apply_filters actually calls the filter function
to APPLY it.
$var1 = apply_filters(‘mypluginfilter’,$var1,$var2);
• NOTE:
– $var1 MUST be specified and be initialised –
i.e $var1 must exist when applying the filter
– apply_filters returns a value, so assign the
result to a variable.

13. Anatomy of Filter
• Creating the filter is done using
add_filter($tag,$function,$priority,$args)
$tag – is the filter you want to ‘hook to’
$function – the function you want to ‘hook’.
$priority – the order. 10 is default, 1 is the
highest.
$args – the number of arguments to pass to
the filter

14. Example Filter function
<?php
function myfilter($var1, $var2=null) {
if ($var2==null) {
$var1 = ‘This is ‘.$var1;
} else {
$var1 =$var2.$var1;
}
return $var1;
}
add_filter(‘mypluginfilter’,’myfilter’,10,2)
?>
This will run ‘myfilter’, when the filter ‘mypluginfilter’ is applied,
pass 2 arguments & return $var1 to be displayed / used.

15. Filters: Some Uses
• Modifying ‘the content’
– Remove shortcodes
– Strip tags / html
– Add elements
• Add custom classes to the Body and Post tags
• Processing Shortcodes in Widgets
– add_filter(‘widget_text’,’do_shortcode’);
• Changing Widget Titles
• Adding functions to WP Nav Menu’s

16. HINT
You can add actions and filters to your
plugins to make them more extendable
Some examples:
• WooCommerce
• WP E Commerce
• Gravity Forms
• Duplicate Post

17. Other stuff to consider
• Namespace
– Create unique functions name! Use a prefix or suffix
or, better yet, use a CLASS!
• Only load functions when needed
– Become familiar with conditional functions to keep
your load time tight
• Security!
– Make use of Wordpress & PHP functions for security:
• esc_html(), esc_attr(), esc_js(), esc_textarea() esc_url(),
wp_nonce_field(), wp_verify_nonce()

18. Useful Resources
• Wordpress API
http://codex.wordpress.org/Plugin_API
• Wordpress Action Reference
http://codex.wordpress.org/Plugin_API/Action_Reference
• Wordpress Filter Reference
http://codex.wordpress.org/Plugin_API/Filter_Reference
• PHP Xref for Wordpress
http://phpxref.com/xref/wordpress/

19. Any Questions?
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charlyjl
tickets@askcharlyleetham.com
www.AskCharlyLeetham.com

20. CODE EXAMPLES...

21. Loading Scripts
• Enqueue Scripts (wp_enqueue_scripts)
Wrong:
<script type=“text/javascript” src=http://mydomain.com/path/script.js>
Right:
<?php
function add_my_script() {
if (!ismypage) { return; }
$src = get_stylesheet_directory_uri().’/path/myscript.js’;
wp_enqueue_script(‘myscript‘,$src,array(‘jquery’),’1.0’,true );
}
add_action('wp_enqueue_scripts', ‘add_my_script‘,10);
?>

22. Loading StyleSheets
• Enqueue Styles
Wrong:
<link type=“text/css” href=“http://mydomain.com/path/style.css”>
Right:
<?php
function add_my_style() {
If (!ismypage) { return; }
$src = get_stylesheet_directory_uri().’/path/style.css’;
$dep = get_stylesheet_directory_uri().’/path/layout.css’;
wp_enqueue_style(‘mystyle‘,$src,$dep,’1.0’,’screen’ );
}
add_action('wp_enqueue_scripts', ‘add_my_style‘,10);
?>

23. Recording user access
• wp_login
<?php
function my_login_function($login) {
$user = get_userdatabylogin($login);
$userid=$user->ID;
//code to record login details
}
add_action('wp_login', ‘my_login_function’, 10,1);

24. Filter Example
$var1 = ‘My Title’;
$var2 = ‘>>>>’;
$var1 = apply_filters(‘mypluginfilter’,$var1,$var2);
echo $var1;
Will return:
>>>> My Title

25. Filter Example
$var1 = ‘My Title’;
$var1 = apply_filters(‘mypluginfilter’,$var1,$var2);
echo $var1;
Will return:
This is My Title