An Activity predstavlja jedan zaslon s korisničkim sučeljem — temeljnu Android komponentu. Njegov životni ciklus (slijed stanja i callback-a dok se kreira, prikazuje, skriva i uništava) ključan je za razumijevanje kako pravilno upravljati resursima i stanjem.
Što je Activity
An ACTIVITY = one screen of the app (a UI the user interacts with):
→ an app is typically several activities (a login screen, a home screen, etc.)
→ the OS manages activities and calls LIFECYCLE methods as their state changes
Životni ciklus Activity-ja
Key lifecycle callbacks (the OS calls these as the activity's state changes):
onCreate() → activity is being CREATED → initialize UI, set up (called once)
onStart() → becoming VISIBLE to the user
onResume() → now in the FOREGROUND, interactive (user can interact)
onPause() → losing focus (another activity coming in front) → pause/save lightly
onStop() → no longer VISIBLE → release resources, stop heavy work
onDestroy() → being DESTROYED → final cleanup
→ Flow: onCreate → onStart → onResume → [running] → onPause → onStop → onDestroy
