Hooks WCSD12

WordPress Hooks
Actions and Filters
WordCamp San Diego 2012

Jeffrey Zinn
ocean goer, wordpress fanboy,
avid backpacker, euro gamer,
soccer hooligan,
voracious coffee drinker

• co-founder of pixel jar
• wordcamp oc co-organizer
• adsanity co-developer
• @jeffreyzinn
• jeff@jzinn.us

What are Hooks?
• 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.

• 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 its PHP functions is executed to modify
specific types of text at these times, using the Filter API.

Wait...What are Hooks?

•Actions - Do Stuff
• Filters - Change Stuff

Why Hooks?

• Crack into code without editing core ﬁles
• Let others alter your work

Hypothetical
Let’s say we were desperate for a widget to place in
our sidebar that displays the word “awesome.”

Basic Awesome Widget

activate

sidebar

activate

sidebar

activate

test

Hypothetical
Upon further consideration you realize this widget is
sorely lacking in puppy pictures. Now what? Let’s
look in the code...

Basic Widget Code
public function widget( $args, $instance ) {

extract( $args );

$title = $instance['title'];

echo $before_widget;

if ( ! empty( $title ) )

echo $before_title . $title . $after_title;

echo '<h2>awesome</h2>';

echo $after_widget;
}

Deluxe Awesome Widget

t
wi dge
sam
e

Deluxe Widget Code

extract( $args );

$title = apply_filters( 'widget_title', $instance['title'] );




do_action( 'before_awesome_widget' );

echo apply_filters( 'filter_awesome_text', '<h2>awesome</h2>' );

do_action( 'after_awesome_widget' );

echo $after_widget;
}

Deluxe Widget Code

extract( $args );
ﬁlter!








echo $after_widget;
}

Deluxe Widget Code

extract( $args );
ﬁlter!





action! do_action( 'before_awesome_widget' );



echo $after_widget;
}

Deluxe Widget Code

extract( $args );
ﬁlter!





action!


ﬁlter!



echo $after_widget;
}

Deluxe Widget Code

extract( $args );
ﬁlter!





action!


ﬁlter!


action!


echo $after_widget;
}

Actions
(do stuff)
• do_action() - Creates a hook for attaching actions via
add_action()

• add_action() - Hooks a function onto a speciﬁc action
created with do_action()

• remove_action() - Removes a function attached to a
speciﬁed action hook

Actions: do_action()
do_action( $tag, $arg, $extra_arg );

• $tag - (string) (required) The name of the hook you wish to create.
Default: None

• $arg - (mixed) (optional) The list of arguments this hook accepts.
Default: ''

...their code...

Actions: add_action()
add_action( $tag, $function_to_add, $priority, $accepted_args );

• $tag - (string) (required) The name of the action you wish to hook onto. Default:
None

• $function_to_add - (callback) (required) The name of the function you wish to be
called. Default: None

• $priority - (int) (optional) How important your function is. Alter this to make your
function be called before or after other functions. Default: 10

• $accepted_args - (int) (optional) How many arguments your function takes. Default: 1

...our code...

Deluxe Widget Code

extract( $args );





action! do_action( 'before_awesome_widget' );



echo $after_widget;
}


which action? which function of ours?

add_action( ‘before_awesome_widget’, ‘puppy’ );

function puppy() {
$src = 'http://placedog.com/g/188/150';
echo '<img src="' . $src . '" />';
}

...in your functions.php script....


which action? which function of ours?


function puppy() {
echo '<img src="' . $src . '" />';
}
Use a unique function name


Multiple Calls to Action
function puppy() {
echo '<img src="' . $src . '" />';
}

add_action( ‘before_awesome_widget’, ‘warning’ );
function warning() {
echo '<p>Warning: puppies!</p>';
}


function puppy() {

Same
echo '<img src="' . $src . '" />';

Action
}

}


function puppy() {

Diff. F
Same
echo '<img src="' . $src . '" />';

unctio
Action
}

ns
}


Action: before_awesome_widget
Function: puppy

Function: puppy

Function: warning

Ordering Actions
add_action( ‘before_awesome_widget’, ‘puppy’, 2 );
function puppy() {
echo '<img src="' . $src . '" />';
$priority (default 10)
}

add_action( ‘before_awesome_widget’, ‘warning’, 1 );
}


Ordering Actions
Function: warning
Priority: 1

Ordering Actions
Function: warning
Priority: 1

Function: puppy
Priority: 2

Actions: remove_action()
remove_action( $tag, $function_to_remove, $priority, $accepted_args );

remove_action( 'before_awesome_widget', 'warning', 1 );

Actions: remove_action()
remove_action( $tag, $function_to_remove, $priority, $accepted_args );

remove_action( 'before_awesome_widget', 'warning', 1 );

Be as speciﬁc as
the original action

Deluxe Widget Code

extract( $args );






ﬁlter!



echo $after_widget;
}

Filters
(change text)
• apply_filters() - Calls the functions added to a filter
hook via
add_filter()

• add_filter() - Hooks a function onto a specific filter
action created with add_filters()

• remove_filter() - Removes a function attached to a
specified filter action hook

Filters: apply_filters()
apply_filters( $tag, $value, $var ... );

• $tag - (string) (required) The name of the filter hook.
Default: None

• $value - (mixed) (required) The value which the filters
hooked to $tag may modify.
Default: None

• $var - (mixed) (optional) One or more additional
variables passed to the filter functions.
Default: None

Filters: add_filter()
add_filter( $tag, $function_to_add, $priority, $accepted_args );

• $tag - (string) (required) The name of the filter to hook the $function_to_add
to. Default: None

• $function_to_add - (callback) (required) The name of the function to be called
when the filter is applied. Default: None

• $priority - (int) (optional) Used to specify the order in which the functions
associated with a particular action are executed. Functions with the same
priority are executed in the order in which they were added to the action.
Default: 10

• $accepted_args - (int) (optional) Number of arguments the function(s) accept
(s). Default: 1


which filter? which function of ours?

add_filter( ‘filter_awesome_text’, ‘filter_awesome’ );

function filter_awesome( $text ) {
$text .= ‘<h4>puppies</h4>’;

return $text;
}





return $text;
} Use a unique function name





return $text;
}





return $text;
}
always return!



return $text;
}

add_filter( ‘filter_awesome_text’, ‘second_filter’ );
function second_filter( $text ) {
$text = ‘<h2>dogs!</h2>’;
return $text;
}



add_filter( ‘filter_awesome_text’, ‘filter_awesome’, 2 );
return $text;
}

add_filter( ‘filter_awesome_text’, ‘second_filter’, 1 );
function second_filter( $text ) {
$text = ‘<h2>dogs!</h2>’;
return $text;
}


remove_filter()
remove_filter( $tag, $function_to_remove, $priority, $accepted_args );

remove_filter( 'the_content', 'wpautop' );

Ridiculous Filter

extract( $args );





do_action( 'before_ridiculous_widget' );

$wrap = ( is_home() ) ? 'h2' : 'h3';

$text = 'awesome';

$pattern = '<%s class="awesome">%s</%s>';

$awesome = sprintf( $pattern, $wrap, $text, $wrap );

echo apply_ﬁlters( 'ﬁlter_ridiculous_text', $awesome, $wrap, $text );

do_action( 'after_ridiculous_widget' );

echo $after_widget;
}

Ridiculous Filter

extract( $args );





do_action( 'before_ridiculous_widget' );

$wrap = ( is_home() ) ? 'h2' : 'h3';

$text = 'awesome';

$pattern = '<%s class="awesome">%s</%s>';


ﬁlter!


do_action( 'after_ridiculous_widget' );

echo $after_widget;
}

Ridiculous Filter
$wrap = ( is_home() ) ? 'h2' : 'h3';
$text = 'awesome';
$pattern = '<%s>%s</%s>';


Ridiculous Filter
$wrap = ( is_home() ) ? 'h2' : 'h3';
$text = 'awesome';


is_home() !is_home()

<h2>awesome</h2> <h3>awesome</h3>

Ridiculous Filter
$wrap = ( is_home() ) ? 'h2' : 'h3';
$text = 'awesome';

??????


is_home() !is_home()

<h2>awesome</h2> <h3>awesome</h3>


...assume is_home()...

add_filter( 'filter_ridiculous_text', 'ridiculous_filter', 10, 3 );

function ridiculous_filter( $text, $var1, $var2 ) {

$var2 = "not awesome";

$new = sprintf( '<%s>%s</%s>', $var1, $var2, $var1 );

return $new;
}



...assume is_home()... <h2>awesome</h2>





return $new;
}



...assume is_home()... <h2>awesome</h2> h2





return $new;
}



...assume is_home()... <h2>awesome</h2> h2 awesome





return $new;
}


Other Themes and Plugins?
• WordPress: 790+ actions, 1250+ filters

• Genesis Framework: 180+ actions; 100+ filters

• Gravity Forms: 120+ actions; 270+ filters

• Shopp: 130+ actions; 230+ filters

Where Hooks?
• Plugin/Theme Wiki

• Documentation

• Actual Code
(search for do_action and apply_ﬁlters)

• Google search!
• http://codex.wordpress.org/Plugin_API

Yes, Hooks!

•Actions - Do Stuff
• Filters - Change Stuff

do_action( ‘the_end’ )
add_action( ‘the_end’, ‘questions’ );
function questions() {
echo ‘Are there any questions?’;
}

slides: http://slideshare.net/jeffreyzinn/hooks-wcsd12
code: https://gist.github.com/2163780

Hooks WCSD12

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