Activation / Deactivation Hooks

Activation and deactivation hooks provide ways to perform actions when plugins are activated or deactivated.

On activation, plugins can run a routine to add rewrite rules, add custom database tables, or set default option values.

On deactivation, plugins can run a routine to remove temporary data such as cache and temp files and directories.

Alert:
The deactivation hook is sometimes confused with the uninstall hook. The uninstall hook is best suited to delete all data permanently such as deleting plugin options and custom tables, etc.

Activation Activation

To set up an activation hook, use the register_activation_hook() function:

register_activation_hook( __FILE__, 'pluginprefix_function_to_run' );

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Deactivation Deactivation

To set up a deactivation hook, use the register_deactivation_hook() function:

register_deactivation_hook( __FILE__, 'pluginprefix_function_to_run' );

The first parameter in each of these functions refers to your main plugin file, which is the file in which you have placed the plugin header comment. Usually these two functions will be triggered from within the main plugin file; however, if the functions are placed in any other file, you must update the first parameter to correctly point to the main plugin file.

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Example Example

One of the most common uses for an activation hook is to refresh WordPress permalinks when a plugin registers a custom post type. This gets rid of the nasty 404 errors.

Let’s look at an example of how to do this:

/**
 * Register the "book" custom post type
 */
function pluginprefix_setup_post_type() {
	register_post_type( 'book', ['public' => true ] ); 
} 
add_action( 'init', 'pluginprefix_setup_post_type' );


/**
 * Activate the plugin.
 */
function pluginprefix_activate() { 
	// Trigger our function that registers the custom post type plugin.
	pluginprefix_setup_post_type(); 
	// Clear the permalinks after the post type has been registered.
	flush_rewrite_rules(); 
}
register_activation_hook( __FILE__, 'pluginprefix_activate' );

If you are unfamiliar with registering custom post types, don’t worry – this will be covered later. This example is used simply because it’s very common.

Using the example from above, the following is how to reverse this process and deactivate a plugin:

/**
 * Deactivation hook.
 */
function pluginprefix_deactivate() {
	// Unregister the post type, so the rules are no longer in memory.
	unregister_post_type( 'book' );
	// Clear the permalinks to remove our post type's rules from the database.
	flush_rewrite_rules();
}
register_deactivation_hook( __FILE__, 'pluginprefix_deactivate' );

For further information regarding activation and deactivation hooks, here are some excellent resources: