I have an app, one activity, with BottomNavigationView and Fragment:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/nav_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="@menu/bottom_nav_menu" />
<fragment
android:id="@+id/nav_host_fragment_activity_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@id/nav_view"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/mobile_navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>
And four fragments, I navigate like this, in MainActivity:
val navController = findNavController(R.id.nav_host_fragment_activity_main)
binding.navView.setupWithNavController(navController)
binding.navView.setOnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_fra1 -> {
findNavController(R.id.nav_host_fragment_activity_main).navigate(R.id.Fragment)
}
R.id.navigation_fra2 -> {
findNavController(R.id.nav_host_fragment_activity_main).navigate(R.id.Fragment2)
}
R.id.navigation_fra3 -> {
findNavController(R.id.nav_host_fragment_activity_main).navigate(R.id.Fragment3)
}
R.id.navigation_fra4 -> {
findNavController(R.id.nav_host_fragment_activity_main).navigate(R.id.Fragment4)
}
}
true
}
Fragments are all the same but pull different data from Firebase Database:
class Fragment : Fragment() {
private var _binding: FragmentBinding? = null
private val binding get() = _binding!!
private lateinit var arrayList: ArrayList<FireItems>
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
_binding = FragmentBinding.inflate(inflater, container, false)
val view = binding.root
arrayList = ArrayList()
val database = Firebase.database
val myRef = database.getReference("items")
myRef.addValueEventListener(object : ValueEventListener {
@SuppressLint("NotifyDataSetChanged")
override fun onDataChange(dataSnapshot: DataSnapshot) {
val value = dataSnapshot.value
arrayList.clear()
Log.d("mDatabase", "Value is: $value")
for (postSnapshot in dataSnapshot.children) {
arrayList.add(FireItems(postSnapshot.child("image").value.toString(), postSnapshot.child("name").value.toString(), postSnapshot.child("description").value.toString()))
if (!arrayList.isNullOrEmpty()) {
binding.apply {
progressCircular.visibility = View.GONE
recyclerView.setHasFixedSize(true)
val adapter = FireRecyclerViewAdapter(requireActivity(), arrayList)
recyclerView.layoutManager = GridLayoutManager(requireActivity(), 2)
recyclerView.adapter = adapter
}
}
}
}
override fun onCancelled(error: DatabaseError) {
Log.w("mDatabase", "Failed to read value.", error.toException())
}
})
requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {}
})
return view
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
I need to make it so that when I move from one fragment to another through the BottomNavigationView, fragments are not recreated each time. Because, firstly, if there are a lot of elements in the list, I don’t want to have to scroll through the entire recycler every time, and secondly, pulling the database every time is not correct as far as I know. Please tell me how to do it better?