Pass variable from action back to template

Question

I'm new to developing with WordPress. I read here that a good way to process data posted from forms is to insert an action on the init function like so:

add_action( 'init', 'contact_form_send_email' );

My function seems to be processing the data correctly, but I can't figure out how to make a variable available within the same template that has the form.

What is the way to do this? I've heard that setting global variables is not a good way to go.

Answer 1

The difference between add_action() and add_filter() is semantic not technical, except that a filter expects a returned value and an action does/will not. The question is whether contact_form_send_email() needs to be called-at /hooked-to init.

If not, you can define your filter in the template with apply_filters(), and then hook to it to run your function and return a value to it.

In template page:

$some_variable = 'some value';
$some_variable = apply_filters('my_filter_hook', $some_variable);

In functions.php

add_filter('my_filter_hook', 'contact_form_send_email', 10, 1 );

function contact_form_send_email( $some_variable ) {
    //do stuff
    $some_variable = 'some new value';

    return $some_variable;

}

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To help determine where you need to hook, this Actions Reference can be useful. Scroll down and you will see some template specific hooks as well.

Answer 2

There's an interesting feature in the WordPress that you might find it useful in situations like this. It's the ability to add something into the cache and retrieve it later.

Since you are hooking into the init, you can retrieve your cache afterward. This is done by using the wp_cache_add() function:

wp_cache_add( $key, $data, $group, $expire );

Add whatever data you wish, and then fetch them on your template:

wp_cache_get( $key, $group );

You can also delete the cache afterward if you wish. Take a look at this codex page.