How to properly setup an activation hook

Question

I am trying to register an activation hook for my plugin. The plugin is using classes and the actual activation method is held in a separate admin class. Reading the documentation for register_activation_hook() it seems like the first parameter $file should always be the file of the main plugin file:

Path to the main plugin file inside the wp-content/plugins directory. A full path will work.

The two classes are kept in separate files, which looks something like this.

This is the main plugin file:

<?php 
/* my-plugin.php */

include_once(plugin_dir_path(__FILE__) . '/admin/my-plugin-admin.php');

register_activation_hook(__FILE__, array('MyPluginAdmin', 'activate'));

class MyPlugin {
}

While this is the admin part, which also contains the activation routine:

<?php
/* my-plugin-admin.php */

class MyPluginAdmin {
  public static function activate() {
    // This method is called in both cases,
    // but in the first example a php warning is generated
  }
}

My problem is that static activate method is actually triggered on activation, but I still get a php warning which looks like this:

PHP Warning:  call_user_func_array() expects parameter 1 to be a valid callback, class 'MyPluginAdmin' not found in /var/www/html/wp/wp-includes/class-wp-hook.php on line 287
PHP Stack trace:
1. {main}() /var/www/html/wp/wp-admin/plugins.php:0
2. activate_plugin($plugin = 'my-plugin/my-plugin.php', $redirect = 'http://localhost/wp/wp-admin/plugins.php?error=true&plugin=my-plugin%2Fmy-plugin.php', $network_wide = FALSE, $silent = *uninitialized*) /var/www/html/wp/wp-admin/plugins.php:43
3. do_action($tag = 'activate_my-plugin/my-plugin.php', $arg = FALSE) /var/www/html/wp/wp-admin/includes/plugin.php:586
4. WP_Hook->do_action($args = array (0 => FALSE)) /var/www/html/wp/wp-includes/plugin.php:453
5. WP_Hook->apply_filters($value = '', $args = array (0 => FALSE)) /var/www/html/wp/wp-includes/class-wp-hook.php:311
6. call_user_func_array:{/var/www/html/wp/wp-includes/class-wp-hook.php:287}(array (0 => 'MyPluginAdmin', 1 => 'activate'), array (0 => FALSE)) /var/www/html/wp/wp-includes/class-wp-hook.php:287

If I change the call to register_activation_hook() into:

register_activation_hook(plugin_dir_path(__FILE__) . '/admin/my-plugin-admin.php', array('MyPluginAdmin', 'activate'));

Then the warning message disappears. So, my question is what is the correct way to use register_activation_hook() and why does it work in both above cases although it throws a warning in the first scenario?

Answer 1

You first example looks corrent. There is however a typo, hence class 'MyPluginAdmin' not found.

You include myplugin-admin.php, but then your question seems to suggest the page holding the class is in fact my-plugin-admin.php (with a hypen).

If I correct the typo and run the code there are no warnings.

Edit (this works correctly):

my-plugin.php:

<?php 
/*
Plugin Name: my-plugin.php
*/

include_once(plugin_dir_path(__FILE__) . '/my-plugin-admin.php');

register_activation_hook(__FILE__, array('MyPluginAdmin', 'activate'));

class MyPlugin {
}

my-plugin-admin.php:

<?php
/* my-plugin-admin.php */

class MyPluginAdmin {
  public static function activate() {
  }
}

With my-plugin.php and my-plugin-admin.php both in the same directory. Does my-plugin-admin.php have the correct permissions?