How to implement a program user status tracking system implemented in C#?

Question

User interface

I am writing a program in C # (based on the viber principle), I can’t figure out how to implement a system for tracking user actions to display an ONLINE / OFFLINE identifier.
Please suggest the principle of implementing such a system (so far, I’m not very strong in programming).

Answer 1

Option two - the client periodically sends a special request that he is online.
Option two - if the client has done some activity recently, then he is online.
More specific can only be said to a more specific question

Answer 2

What is the protocol for client-server communication?
If TCP, then you can simply poll the connection status and keep it ESTABLISHED all the time. True, this approach is suitable for a relatively small number of customers. If their account went into the thousands, then yes, you need to interrogate periodically.