Stop Hacking Wordpress

Start Working With It!

Charly Leetham

www.AskCharlyLeetham.com

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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

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...

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

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...

• 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!

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.

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

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.

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

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.

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

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.

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

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

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()

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/

Any Questions?

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CODE EXAMPLES...

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);

?>

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);

?>

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);

Filter Example

$var1 = ‘My Title’;

$var2 = ‘>>>>’;

$var1 = apply_filters(‘mypluginfilter’,$var1,$var2);

echo $var1;

Will return:

>>>> My Title

Filter Example

$var1 = ‘My Title’;

$var1 = apply_filters(‘mypluginfilter’,$var1,$var2);

echo $var1;

Will return:

This is My Title