Controller can load Addons from actions method. We load the addons which are set to OnRequest status.
 
Following variable used to load addons
$this->addons = Array([Addon1],[Addon2]...[AddonN]);
 
For example:

$this->addons = Array('validation','rich_text_editor','row_manager');
 

Important: It's good practice to load addons from action controller because related resource load only on that Action Method scope and page can get relief from unnecessary load.