I'm using 2 components of the jetpack: Paging library and Navigation.
In my case, I have 2 fragment: ListMoviesFragment & MovieDetailFragment
when I scroll a certain distance and click a movie item of the recyclerview, MovieDetailFragment is attached and the ListMoviesFragment is in the backstack. Then I press back button, the ListMoviesFragment is bring back from the backstack.
The point is scrolled position and items of the ListMoviesFrament are reset exactly like first time attach to its activity. so, how to keep states of recyclerview to prevent that?
In another way, how to keep states of whole fragment like hide/show a fragment with FragmentTransaction in traditional way but for modern way(navigation)
My sample codes:
fragment layout:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="net.karaokestar.app.SplashFragment">
<TextView
android:id="@+id/singer_label"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:text="Ca sĩ"
android:textColor="@android:color/white"
android:layout_alignParentLeft="true"
android:layout_toLeftOf="@+id/btn_game_more"
android:layout_centerVertical="true"
android:background="@drawable/shape_label"
android:layout_marginTop="10dp"
android:layout_marginBottom="@dimen/header_margin_bottom_list"
android:textStyle="bold"
android:padding="@dimen/header_padding_size"
android:textAllCaps="true"/>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/list_singers"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
Fragment kotlin code:
package net.karaokestar.app
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import androidx.navigation.fragment.findNavController
import androidx.paging.LivePagedListBuilder
import androidx.paging.PagedList
import androidx.recyclerview.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.fragment_splash.*
import net.karaokestar.app.home.HomeSingersAdapter
import net.karaokestar.app.home.HomeSingersRepository
class SplashFragment : Fragment() {
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_splash, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val singersAdapter = HomeSingersAdapter()
singersAdapter.setOnItemClickListener{
findNavController().navigate(SplashFragmentDirections.actionSplashFragmentToSingerFragment2())
}
list_singers.layoutManager = LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false)
list_singers.setHasFixedSize(true)
list_singers.adapter = singersAdapter
getSingersPagination().observe(viewLifecycleOwner, Observer {
singersAdapter.submitList(it)
})
}
fun getSingersPagination() : LiveData<PagedList<Singer>> {
val repository = HomeSingersRepository()
val pagedListConfig = PagedList.Config.Builder().setEnablePlaceholders(true)
.setPageSize(Configurations.SINGERS_PAGE_SIZE).setPrefetchDistance(Configurations.SINGERS_PAGE_SIZE).build()
return LivePagedListBuilder(repository, pagedListConfig).build()
}
}