Thanks for the quick reponses, @PVince81 and @patrickjahns !
I wrongly used \OCP\Files to listen upon, but now that I changed it to $this->root->listen('\OC\Files', 'postWrite', $callbackPostWrite); it still doesn’t work 
Thanks for the quick reponses, @PVince81 and @patrickjahns !
I wrongly used \OCP\Files to listen upon, but now that I changed it to $this->root->listen('\OC\Files', 'postWrite', $callbackPostWrite); it still doesn’t work