Function not working on any file other than the main plugin file

Question

My plugin has several php files that are included on the main plugin file. I am using some functions on the other files but they don't work there. They work when I use them on the main plugin file.

For example,

On the main plugin file "test-plugin.php"

<?php
/*
Plugin Name: Test Plugin
Description: test
Version: 1.0
*/

include_once( plugin_dir_path( __FILE__ ) . 'test-file.php' );

On the other file "test-file.php" (same directory with test-plugin.php)

<?php

function enable_user_registration() {
    if(!get_option('users_can_register')) {
        update_option( 'users_can_register', '1' );
    }
}

register_activation_hook( plugin_dir_path(__FILE__), 'enable_user_registration' );

Regards..

Answer 1

I guess you should be using register_activation_hook() with the full path including filename, not just the path:

register_activation_hook( plugin_dir_path(__FILE__) . 'test-plugin.php', 'enable_user_registration' );

Answer 2

The first argument of register_activation_hook() is the plugin filename including the path, so you need __FILE__ instead of plugin_dir_path( __FILE__ ).

// This should be in main plugin file
register_activation_hook( __FILE__, 'enable_user_registration' );
function enable_user_registration() {
    if(!get_option('users_can_register')) {
        update_option( 'users_can_register', '1' );
    }
}

It is common to register the activation hook in the main plugin file, but the callback can be defined in any file you wish.

For example, in test-file.php you can define the callback:

function enable_user_registration() {
    if(!get_option('users_can_register')) {
        update_option( 'users_can_register', '1' );
    }
}

And in the main plugin file you can register the activation hook:

/*
Plugin Name: Test Plugin
Description: test
Version: 1.0
*/

include_once( plugin_dir_path( __FILE__ ) . 'test-file.php' );
register_activation_hook( __FILE__, 'enable_user_registration' );

You could also store the value of __FILE__ from the main plugin file in a constant, so you don't need to harcode any file name or file path:

/*
Plugin Name: Test Plugin
Description: test
Version: 1.0
*/

define( 'MY_PLUGIN_FILE_PATH', __FILE__ );
define( 'MY_PLUGIN_DIR_PATH', plugin_dir_path( __FILE__ ) );
include_once( MY_PLUGIN_DIR_PATH . 'test-file.php' );

And then, in test-file.php:

register_activation_hook( MY_PLUGIN_FILE_PATH, 'enable_user_registration' );
function enable_user_registration() {
    if(!get_option('users_can_register')) {
        update_option( 'users_can_register', '1' );
    }
}