A Fragment is a reusable portion of UI with its own lifecycle, hosted inside an Activity. Modern apps often use one Activity + many Fragments (or fully Compose).
A basic Fragment
class HomeFragment : Fragment(R.layout.fragment_home) {
override fun onViewCreated(v: View, s: Bundle?) {
super.onViewCreated(v, s)
// set up views here, not in onCreate
}
}Why fragments?
- Reuse the same UI on phones and tablets.
- Power bottom-navigation tabs and view-pager swipes.
- Swap sections without launching a whole new Activity.
Common mistake: Use
viewLifecycleOwner (not the fragment itself) when observing LiveData/Flow in a fragment, or you'll leak the old view.Summary
Fragments let you compose flexible, reusable screens inside a host Activity, each with its own lifecycle.