can I pass arguments to my function through add_action?

can I do something like that? to pass arguments to my function? I already studied add_action doc but did not figure out how to do it. What the exact syntax to pass two arguments would look like. In particular how to pass text & integer arguments.

function recent_post_by_author($author,$number_of_posts) {
  some commands;
}
add_action('thesis_hook_before_post','recent_post_by_author',10,'author,2')

UPDATE

it seems to me that it is done somehow through do_action but how? :-)

can I do something like that? to pass arguments to my function?

Yes you can! The trick really is in what type of function you pass to add_action and what you expect from do_action.

‘my_function_name’
array( instance, ‘instance_function_name’)
‘StaticClassName::a_function_on_static_class'
anonymous
lambda
closure

We can do it with a closure.

// custom args for hook

$args = array (
    'author'        =>  6, // id
    'posts_per_page'=>  1, // max posts
);

// subscribe to the hook w/custom args

add_action('thesis_hook_before_post', 
           function() use ( $args ) { 
               recent_post_by_author( $args ); });


// trigger the hook somewhere

do_action( 'thesis_hook_before_post' );


// renders a list of post tiles by author

function recent_post_by_author( $args ) {

    // merge w/default args
    $args = wp_parse_args( $args, array (
        'author'        =>  -1,
        'orderby'       =>  'post_date',
        'order'         =>  'ASC',
        'posts_per_page'=>  25
    ));

    // pull the user's posts
    $user_posts = get_posts( $args );

    // some commands
    echo '<ul>';
    foreach ( $user_posts as $post ) {
        echo "<li>$post->post_title</li>";
    }
    echo '</ul>';
}

Here is a simplified example of a closure working

$total = array();

add_action('count_em_dude', function() use (&$total) { $total[] = count($total); } );

do_action ('count_em_dude' );
do_action ('count_em_dude' );
do_action ('count_em_dude' );
do_action ('count_em_dude' );
do_action ('count_em_dude' );
do_action ('count_em_dude' );
do_action ('count_em_dude' );

echo implode ( ', ', $total ); // 0, 1, 2, 3, 4, 5, 6

Anonymous vs. Closure

add_action ('custom_action', function(){ echo 'anonymous functions work without args!'; } ); //

add_action ('custom_action', function($a, $b, $c, $d){ echo 'anonymous functions work but default args num is 1, the rest are null - '; var_dump(array($a,$b,$c,$d)); } ); // a

add_action ('custom_action', function($a, $b, $c, $d){ echo 'anonymous functions work if you specify number of args after priority - '; var_dump(array($a,$b,$c,$d)); }, 10, 4 ); // a,b,c,d

// CLOSURE

$value = 12345;
add_action ('custom_action', function($a, $b, $c, $d) use ($value) { echo 'closures allow you to include values - '; var_dump(array($a,$b,$c,$d, $value)); }, 10, 4 ); // a,b,c,d, 12345

// DO IT!

do_action( 'custom_action', 'aa', 'bb', 'cc', 'dd' );

Proxy Function Class

class ProxyFunc {
    public $args = null;
    public $func = null;
    public $location = null;
    public $func_args = null;
    function __construct($func, $args, $location='after', $action='', $priority = 10, $accepted_args = 1) {
        $this->func = $func;
        $this->args = is_array($args) ? $args : array($args);
        $this->location = $location;
        if( ! empty($action) ){
            // (optional) pass action in constructor to automatically subscribe
            add_action($action, $this, $priority, $accepted_args );
        }
    }
    function __invoke() {
        // current arguments passed to invoke
        $this->func_args = func_get_args();

        // position of stored arguments
        switch($this->location){
            case 'after':
                $args = array_merge($this->func_args, $this->args );
                break;
            case 'before':
                $args = array_merge($this->args, $this->func_args );
                break;
            case 'replace':
                $args = $this->args;
                break;
            case 'reference':
                // only pass reference to this object
                $args = array($this);
                break;
            default:
                // ignore stored args
                $args = $this->func_args;
        }

        // trigger the callback
        call_user_func_array( $this->func, $args );

        // clear current args
        $this->func_args = null;
    }
}

Example Usage #1

$proxyFunc = new ProxyFunc(
    function() {
        echo "<pre>"; print_r( func_get_args() ); wp_die();
    },
    array(1,2,3), 'after'
);

add_action('TestProxyFunc', $proxyFunc );
do_action('TestProxyFunc', 'Hello World', 'Goodbye'); // Hello World, 1, 2, 3

Example Usage #2

$proxyFunc = new ProxyFunc(
    function() {
        echo "<pre>"; print_r( func_get_args() ); wp_die();
    },                  // callback function
    array(1,2,3),       // stored args
    'after',            // position of stored args
    'TestProxyFunc',    // (optional) action
    10,                 // (optional) priority
    2                   // (optional) increase the action args length.
);
do_action('TestProxyFunc', 'Hello World', 'Goodbye'); // Hello World, Goodbye, 1, 2, 3

Instead of:

add_action('thesis_hook_before_post','recent_post_by_author',10,'author,2')

it should be:

add_action('thesis_hook_before_post','recent_post_by_author',10,2)

...where 2 is the number of arguments and 10 is the priority in which the function will be executed. You don't list your arguments in add_action. This initially tripped me up. Your function then looks like this:

function function_name ( $arg1, $arg2 ) { /* do stuff here */ }

Both the add_action and function go in functions.php and you specify your arguments in the template file (page.php for example) with do_action like so:

do_action( 'name-of-action', $arg1, $arg2 );

Hope this helps.

Build custom WP functions with classes

This is easy with classes, as you can set object variables with the constructor, and use them in any class method. So for an example, here's how adding meta boxes could work in classes...

// Array to pass to class
$data = array(
    "meta_id" => "custom_wp_meta",
    "a" => true,
    "b" => true,
    // etc...
);

// Init class
$var = new yourWpClass ($data);

// Class
class yourWpClass {

    // Pass $data var to class
    function __construct($init) {
        $this->box = $init; // Get data in var
        $this->meta_id = $init["meta_id"];
        add_action( 'add_meta_boxes', array(&$this, '_reg_meta') );
    }
    public function _reg_meta() {
        add_meta_box(
            $this->meta_id,
            // etc ....
        );
    }
}

If you consider __construct($arg) the same as function functionname($arg) then you should be able to avoid global variables and pass all the information you need through to any functions in the class object.

These pages seem to be good points of reference when building wordpress meta / plugins ->

http://www.deluxeblogtips.com/2010/05/howto-meta-box-wordpress.html
https://gist.github.com/1880770

Basically the do_action is placed where the action should be executed, and it needs a name plus your custom parameters.

When you come to call the function using add_action, pass the name of your do_action() as your first argument, and the function name as the second. So something like:

function recent_post_by_author($author,$number_of_posts) {
  some commands;
}
add_action('get_the_data','recent_post_by_author',10,'author,2');

This is where it's executed

do_action('get_the_data',$author,$number_of_posts);

Should hopefully work.

can I pass arguments to my function through add_action?

Build custom WP functions with classes

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