I'm developing an Android application where the home screen asks for user login login. In a simple way, a user can see the list of other users registered. I now need to implement an asynchronous chat. That is, the logged in user selects a user from the list and can then send a message to those users (only plain text). The other user receives the message (you can view the messages in an icon of your menu) and you can reply again.
How can I do this?