MultiSite, Plugins and Activation in Wordpress

Yes, its possible! WordPress offers for normal Plugins the hook register_activation_hook();. 

This is active right after the activation of a Plugin, so you can start small installation scripts. But if we are in a MultiSite environment (old: MultiUser) and put the Plugin in the folder wp-content/mu-plugins, then the hook doesn't do anything, because the Plugin is automatically activated. But there are few ways you can still have a kind of activation hook. 

One is this option:

• if ( ! class_exists( 'my_mu_plugin' ) ) {
• if ( function_exists( 'add_action' ) ) {
• add_action( 'plugins_loaded' , array( 'my_mu_plugin', 'get_object' ) );
• }
• class my_mu_plugin {
• static private $classobj = NULL;
• public function get_object () {
• if ( NULL === self :: $classobj ) {
• self :: $classobj = new self;
• }
• return self :: $classobj;
• }
• public function __construct () {
• // Fake-Activation-Hook
• $this->activation();
• }
• private function activation () {
• if ( 'activated' == get_blog_option( 1, 'my_mu_plugin_activated' ) ) {
• // Do Stuff during activation
• ...
• // Update Option
• update_blog_option( 1, 'my_mu_plugin_activated', 'activated' );
• }
• }
• }
• }

We are doing the following: We check whether a certain option is set in blog 1, if not, then run through an activation function, otherwise do nothing - Blog 1 simple so that the install script is only in blog 1 in use. If you want to use it in all the blogs then simply use the function get_option().

Tweet