When an app show a notification, this come from a server?
Is there a way to send a notification from "inside of the app"?
What happens is there are not internet connection?
The notification never comes?
Its depends on app. if its a static notification you can use Services,Timers,DataBase(Predefined Notification data store) to generate the Notification from app itself without internet. Ex: Predefined Notification to intimate scheduling for every 3 hours.
If you need Dynamic data you need to fetch it from server.