add_filter does not work as expected

Question

I have a wordpress plugin where i included this (with some changes)

$fep_files = array(
    'first' => 'first.php',
    'second' => 'second.php'
);

$fep_files = apply_filters('include_files', $fep_files );

foreach ( $fep_files as $fep_file )
require_once ( $fep_file );
unset ( $fep_files );

Now i added in my theme's function.php

function fep_remove ( $fep_files )
{
    if ( isset ( $fep_files['first'] ) ) {
        unset ( $fep_files['first'] );
            }
        //die($fep_files); //to check it fires
    return $fep_files;
}

add_filter( 'include_files', 'fep_remove' );

It should remove first.php but it does not. i am wrong some where, but where? Is there any better way to include files where user can include/exclude any files if needed?

Answer 1

Your plugin code is going to run before the theme code and hence will run before anything is added to the hook. You will need to the code that processes the file inclusion to some other hook that runs after all of the plugins load, like after_setup_theme

This should help: Is there a flowchart for wordpress loading sequence?

Answer 2

I think there needs to be an update to some of the answers on here. (Just for when I, or others, come upon this page in the future looking for an answer).

Plugin ordering seems to depend on the type of Wordpress installation you are working with. If you are working with a Multisite installation, then plugins are indeed processed in the order in which they are activated.

However, in a single wordpress installation, they are activated alphabetically. So, if you are running into an issue where you need to update an initialization filter or action for another plugin, your best bet is to name your plugin something that begins with an underscore.

For example: _my_custom_plugin/my_custom_plugin.php

For reference. please see 704-713 in wp-admin/includes/plugin.php

Answer 3

The previous answer was great as far as the order, but I could not figure out how to make the filter/hook work with those intructions.

My solution was creating a custom plugin containing the filter on it, making sure that it alphabetically comes before the plugin that contains the filter I want to add.

In other words, put the code in plugings/a-custom-plugin.php starting the file with

<?php
/*
Plugin Name: My Custom Plugin
*/