Passing arguments in add_action inside search template

Question

I'm trying to pass a argument to the function. But it is not transmitted. var_dump produces

string'' (length = 0)

What am I doing wrong?

$map_vars = 'Test';

function map_data($data) {
    var_dump($data);
}

add_action('wp_footer', 'map_data', 10, 1);
do_action( 'map_data', $map_vars );

Answer 1

The footer doesn’t run in the global context, so the variable $map_vars is not in the correct scope.

To keep the variable and the callback in the same scope, you could use a class:

class Map_Var_Example
{
    public static $map_vars;

    public static function map_data()
    {
        var_dump( self::$map_vars );
    }
}

Map_Var_Example::$map_vars = 'Test';

add_action( 'wp_footer', array( 'Map_Var_Example', 'map_data' ), 10, 1 );

Answer 2

I think you have misunderstood actions and hooks.

Your code outputs empty string, because what you do is:

1. Create some function which takes 1 parameter and var_dumps it.
2. Assign this function as action to wp_footer hook. This hook doesn't have any parameters, so WordPress calls your function, during do_action('wp_footer'); without any parameters.
3. Then you call your own do_action('map_data') with some parameters, but you have never assigned any function to this hook. It also isn't default WordPress hook, so there is no function assigned to hook map_data. Ergo nothing will happen.