register_activation_hook vs add_action('init')

Question

I'm trying to determine why some WordPress plugins use register_activation_hook(FILE, 'activate_plugin') while others use the add_action('init', 'activate_plugin');

Answer 1

A few reasons:

• register_activation_hook is WP2+, add_action was available to use before that
• register_activation_hook allows the developer to specify the file the function resides in (although this seems rarely used)
• for me, register_activation_hook is 'cleaner'

So I'd bet that plugins using add_action date from before version 2 or the developer isn't aware of register_activation_hook

Answer 2

The two do different things, register_activation_hook is used to register a function which will be called once when the plug-in is activated (on the Wordpress plug-in management page), where as functions hooked into the init action will be called on every request.

So, a common example would be to use an activation function to create database tables, or set default options for a plug-in and then an init action function to load translated strings.

Answer 3

Hooking an "activate_plugin" function to init looks to either be code done a long time ago, or by someone who doesn't know about register_activation_hook. A third possibility is that despite the function name they want it to run whether or not register_activation_hook is called.

For example, when updating a plugin, the plugin is deactivated and reactivated, but the activate hook is not called. (And it's certainly not called if the plugin is updated via FTP or similar.) So if I were putting in some code that need to run on activate or after an update I might hook it to init.