I really tried to find a solution to this problem but didn't. There are some threads related to this concept, but I didn't find a comprehensive solution.
I have a server with Openfire which sends messages. When both users are online, there is no problem. However, when a user is offline I would like to send a push notification, as in Whatsapp. I heard that Whatsapp and other IM apps use a modified version of ejabber to send push notifications, but couldn't find out how.
One possibility is to use GCM, but I am not sure if this is the right way to go. Also I would like to avoid polling, for the sake of not draining battery life.
Does anyone know some solution to this or has an example?