iOS Structuring for user event sign ups with a server

I'm relatively new to iOS development and I'm trying to create an app where users can login and sign up for events via rest calls to a server.

I don't really know how to approach keeping all the viewControllers updated (for example if I sign up for a event then my profile page should now list the event and the event page itself should show that I'm signed up) based on the state of the user.

Also, If I update the user in the server, do I just manually update the user on the phone and trust everything is synced or for every update to the server I pull all the information for the user every time?

Any who, I guess my biggest question is does anyone know any good design patterns/structuring/tutorials for the app on how to keep all the pages updated based on the user?

I've been trying to google my question but it's hard to get my wording right...

Thanks!