Question

I’m trying to create a hook in one WordPress plugin that could be used by other plugins. First off, is this even possible? I’m also sending some additional args so this may be 2 questions in one since I’ve been having trouble finding definitive information on how to do this.

Here is what I’ve tried so far:

In the plugin that is creating the hook (call it Plugin 1) I added:

do_action('plugin1_hook', $customArg1, $customArg2, $customArg3);

at the point that I want the hook to fire. Then, in a different plugin (Plugin 2), I added:

add_action('plugin1_hook', 'my_function');

and

function my_function($customArg1, $customArg2, $customArg3) { //my code }

This does not seem to be firing the function, however.
My refence for this has been the WordPress hook comment_post, which is defined by WordPress as:

do_action('comment_post', $comment_ID, $commentdata['comment_approved']);

and I am using as:

add_action('comment_post', 'my_comment'); 
function my_comment($comment_id) { //my code }

The above snippet is functioning properly.

Answer 1

I thought I’d post this as an answer as it’s a little clearer to explain 🙂

When you hook a function, but do not specify the number of arguments, WordPress will always pass back one argument.

You won’t get errors for something like this;

function do_my_hook($arg1, $arg2 = '', $arg3 = '') {}
add_action('my_hook', 'do_my_hook');

But you will for something like this;

function do_my_hook($arg1, $arg2, $arg3) {}
add_action('my_hook', 'do_my_hook');

WordPress is trying to call do_my_hook(), but it’s only passing back one argument. The first example uses PHP default function arguments, so that you can call a function without passing all available arguments, but without error.

The second example will trigger a ‘missing argument(s)’ PHP error, as all three arguments are required.

The fix?

add_action('my_hook', 'do_my_hook', 10, 3);

The idea behind defining how many arguments your function takes is to avoid errors like these (though technically they are as easily avoided using default arguments!).