Summary: This appears to be an issue with hosting the RecyclerView inside of a Bottom Sheet as the parent Fragment HomeFragment hosts another instance of the child Fragment ContentFragment which is not nested within a Bottom Sheet and the onRestoreInstanceState performs as expected.
When saving and returning a RecyclerView LayoutManager's state in a Fragment's onSaveInstanceState and onViewStateRestored methods, the expected outcome is for the RecyclerView to display in the same position as prior to the configuration change.
Upon screen configuration change the RecyclerView is sometimes showing at position 0 rather than the RecyclerView position prior to the configuration change. It is also successfully retaining the layout state as expected in some cases. Because of the randomness this seems that a lifecycle + Bottom Sheet issue may be involved.
contentRecyclerView.layoutManager!!.onSaveInstanceState() logged as not null on onSaveInstanceState. savedRecyclerLayoutState logged as not null on onViewStateRestored.savedRecyclerLayoutState logged as not null after the adapter is loaded with data in the SAVED.name case in observeContentUpdated below.Hierarchy
The ContentFragment is hosted by HomeFragment inside a BottomSheet Fragment named bottomSheet in the fragment_home layout. The ContentFragment's fragment_content layout contains the contentRecyclerView.
Loading Saved State
onRestoreInstanceState is called after data has been loaded to the Adapter in observeContentUpdated in the SAVED.name case. The instance state is set to null after onRestoreInstanceState because cells in the RecyclerView are dismissible and will cause data to load again. This ensures the restore only happens once after a config change.
HomeFragment.kt
initSavedBottomSheet creates the Bottom Sheet containing the saved Fragment ContentFragment.
class HomeFragment : Fragment() {
...
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
outState.putParcelable(USER_KEY, user)
outState.putBoolean(APP_BAR_EXPANDED_KEY, isAppBarExpanded)
outState.putBoolean(SAVED_CONTENT_EXPANDED_KEY, isSavedContentExpanded)
}
override fun onViewStateRestored(savedInstanceState: Bundle?) {
super.onViewStateRestored(savedInstanceState)
if (savedInstanceState != null) {
if (savedInstanceState.getBoolean(APP_BAR_EXPANDED_KEY)) appBar.setExpanded(true)
else appBar.setExpanded(false)
if (savedInstanceState.getBoolean(SAVED_CONTENT_EXPANDED_KEY)) {
swipeToRefresh.isEnabled = false
bottomSheetBehavior.state = STATE_EXPANDED
setBottomSheetExpanded()
}
updateAds()
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
homeViewModel = ViewModelProviders.of(activity!!).get(HomeViewModel::class.java)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
binding = FragmentHomeBinding.inflate(inflater, container, false)
binding.setLifecycleOwner(this)
binding.viewmodel = homeViewModel
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
user = homeViewModel.getCurrentUser()
...
observeSignIn(savedInstanceState)
initSavedBottomSheet(savedInstanceState)
...
initSwipeToRefresh()
...
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
if (savedInstanceState == null
&& childFragmentManager.findFragmentByTag(PRICEGRAPH_FRAGMENT_TAG) == null
&& childFragmentManager.findFragmentByTag(CONTENT_FEED_FRAGMENT_TAG) == null) {
childFragmentManager.beginTransaction()
.replace(priceContainer.id, PriceFragment.newInstance(), PRICEGRAPH_FRAGMENT_TAG)
.commit()
childFragmentManager.beginTransaction().replace(contentContainer.id,
ContentFragment.newInstance(Bundle().apply {
putString(FEED_TYPE_KEY, MAIN.name)
}), CONTENT_FEED_FRAGMENT_TAG)
.commit()
}
}
...
private fun initSavedBottomSheet(savedInstanceState: Bundle?) {
bottomSheetBehavior = from(bottomSheet)
bottomSheetBehavior.isHideable = false
bottomSheetBehavior.peekHeight = SAVED_BOTTOM_SHEET_PEEK_HEIGHT
bottomSheet.layoutParams.height = getDisplayHeight(context!!)
if (savedInstanceState == null && homeViewModel.user.value == null)
childFragmentManager.beginTransaction().replace(
R.id.savedContentContainer,
SignInDialogFragment.newInstance(Bundle().apply {
putInt(SIGNIN_TYPE_KEY, FULLSCREEN.code)
}))
.commit()
bottomSheetBehavior.setBottomSheetCallback(object : BottomSheetBehavior.BottomSheetCallback() {
override fun onStateChanged(bottomSheet: View, newState: Int) {
if (newState == STATE_EXPANDED) {
homeViewModel.bottomSheetState.value = STATE_EXPANDED
setBottomSheetExpanded()
}
if (newState == STATE_COLLAPSED) {
isSavedContentExpanded = false
appBar.visibility = VISIBLE
bottom_handle.visibility = VISIBLE
bottom_handle_elevation.visibility = VISIBLE
}
}
override fun onSlide(bottomSheet: View, slideOffset: Float) {}
})
...
}
private fun setBottomSheetExpanded() {
isSavedContentExpanded = true
appBar.visibility = GONE
bottom_handle.visibility = GONE
bottom_handle_elevation.visibility = GONE
}
private fun initSavedContentFragment() {
childFragmentManager.beginTransaction().replace(
savedContentContainer.id,
ContentFragment.newInstance(Bundle().apply { putString(FEED_TYPE_KEY, SAVED.name) }),
SAVED_CONTENT_TAG).commit()
}
...
private fun observeSignIn(savedInstanceState: Bundle?) {
homeViewModel.user.observe(this, Observer { user: FirebaseUser? ->
this.user = user
...
if (user != null) { // Signed in.
...
if (savedInstanceState == null || savedInstanceState.getParcelable<FirebaseUser>(USER_KEY) == null) {
initMainContent()
initSavedContentFragment()
}
} else if (savedInstanceState == null) /*Signed out.*/ initMainContent()
})
}
private fun initMainContent() {
(childFragmentManager.findFragmentById(R.id.contentContainer) as ContentFragment)
.initMainContent(false)
}
fun initSwipeToRefresh() {
homeViewModel.isSwipeToRefreshEnabled.observe(viewLifecycleOwner, Observer { isEnabled: Boolean ->
...
(childFragmentManager.findFragmentById(R.id.priceContainer) as PriceFragment)
.getPrices(false, false)
if (homeViewModel.accountType.value == FREE) updateAds()
}
}
private fun updateAds() {
(childFragmentManager.findFragmentById(R.id.contentContainer) as ContentFragment)
.updateAds(true)
if (childFragmentManager.findFragmentById(R.id.savedContentContainer) as ContentFragment != null)
(childFragmentManager.findFragmentById(R.id.savedContentContainer) as ContentFragment)
.updateAds(true)
}
...
}
ContentFragment.kt
The contentRecyclerView is populated in the initializeAdapters method.
class ContentFragment : Fragment() {
...
private var savedRecyclerLayoutState: Parcelable? = null
companion object {
@JvmStatic
fun newInstance(contentBundle: Bundle) = ContentFragment().apply {
arguments = contentBundle
}
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
if (contentRecyclerView != null)
outState.putParcelable(CONTENT_RECYCLER_VIEW_STATE,
contentRecyclerView.layoutManager!!.onSaveInstanceState())
}
override fun onViewStateRestored(savedInstanceState: Bundle?) {
super.onViewStateRestored(savedInstanceState)
if (savedInstanceState != null) {
savedRecyclerLayoutState = savedInstanceState.getParcelable(CONTENT_RECYCLER_VIEW_STATE)
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
feedType = ContentFragmentArgs.fromBundle(arguments!!).feedType
analytics = getInstance(FirebaseApp.getInstance()!!.applicationContext)
contentViewModel = ViewModelProviders.of(this).get(ContentViewModel::class.java)
homeViewModel = ViewModelProviders.of(activity!!).get(HomeViewModel::class.java)
contentViewModel.feedType = feedType
if (savedInstanceState == null) homeViewModel.isRealtime.observe(this, Observer { isRealtime: Boolean ->
when (feedType) {
SAVED.name, DISMISSED.name -> initCategorizedContent(feedType, homeViewModel.user.value!!.uid)
}
})
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
analytics.setCurrentScreen(activity!!, feedType, null)
binding = FragmentContentBinding.inflate(inflater, container, false)
binding.setLifecycleOwner(this)
binding.viewmodel = contentViewModel
binding.actionbar.viewmodel = contentViewModel
binding.emptyContent.viewmodel = contentViewModel
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setToolbar()
initializeAdapters()
}
override fun onDestroy() {
moPubAdapter.destroy()
compositeDisposable.dispose()
super.onDestroy()
}
fun setToolbar() {
when (feedType) {
SAVED.name -> {
binding.actionbar.toolbar.savedContentTitle.visibility = View.VISIBLE
}
DISMISSED.name -> {
binding.actionbar.toolbar.title = getString(R.string.dismissed)
(activity as AppCompatActivity).setSupportActionBar(binding.actionbar.toolbar)
(activity as AppCompatActivity).supportActionBar!!.setDisplayHomeAsUpEnabled(true)
}
}
}
fun initMainContent(isRealtime: Boolean) {
contentViewModel.initializeMainContent(isRealtime).observe(viewLifecycleOwner, Observer { status ->
if (status == SUCCESS && homeViewModel.accountType.value == FREE) updateAds(true)
})
}
fun initCategorizedContent(feedType: String, userId: String) {
contentViewModel.initCategorizedContent(feedType, userId)
}
fun updateAds(toLoad: Boolean) {
var toLoad = toLoad
moPubAdapter.loadAds(AD_UNIT_ID)
moPubAdapter.setAdLoadedListener(object : MoPubNativeAdLoadedListener {
override fun onAdRemoved(position: Int) {}
override fun onAdLoaded(position: Int) {
if (toLoad) {
moPubAdapter.notifyDataSetChanged()
toLoad = false
}
}
})
}
private fun initializeAdapters() {
contentRecyclerView.layoutManager = LinearLayoutManager(context)
populateAdapterType()
observeContentUpdated()
...
}
private fun observeContentUpdated() {
when (feedType) {
MAIN.name -> {
contentViewModel.getMainContentList().observe(viewLifecycleOwner, Observer { homeContentList ->
adapter.submitList(homeContentList)
if (homeContentList.isNotEmpty()) {
emptyContent.visibility = GONE
if (savedRecyclerLayoutState != null) {
contentRecyclerView.layoutManager?.onRestoreInstanceState(savedRecyclerLayoutState)
savedRecyclerLayoutState = null
}
}
})
}
SAVED.name, DISMISSED.name -> {
contentViewModel.getCategorizedContentList(
if (feedType == SAVED.name) SAVED
else if (feedType == DISMISSED.name) DISMISSED
else NONE
).observe(viewLifecycleOwner, Observer { contentList ->
adapter.submitList(contentList)
if (!(contentList.size == 0 && (adapter.itemCount == 1 || adapter.itemCount == 0))) {
emptyContent.visibility = GONE
if (feedType == SAVED.name) {
if (savedRecyclerLayoutState != null) {
contentRecyclerView.layoutManager?.onRestoreInstanceState(savedRecyclerLayoutState)
savedRecyclerLayoutState = null
}
}
if (feedType == DISMISSED.name)
contentRecyclerView.layoutManager?.onRestoreInstanceState(savedRecyclerLayoutState)
}
})
}
}
}
private fun populateAdapterType() {
adapter = ContentAdapter(contentViewModel)
// FREE
if (homeViewModel.accountType.value!! == FREE) {
moPubAdapter = MoPubRecyclerAdapter(activity!!, adapter,
MoPubNativeAdPositioning.MoPubServerPositioning())
...
contentRecyclerView.adapter = moPubAdapter
// Realtime, only need to set ads once.
if (feedType == SAVED.name || feedType == DISMISSED.name) moPubAdapter.loadAds(AD_UNIT_ID)
} /* PAID */ else contentRecyclerView.adapter = adapter
ItemTouchHelper(homeViewModel).build(context!!, FREE, feedType, adapter, moPubAdapter, fragmentManager!!)
.attachToRecyclerView(contentRecyclerView)
}
...
}
fragment_home.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="viewmodel"
type="app.coinverse.home.HomeViewModel" />
</data>
<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
android:id="@+id/swipeToRefresh"
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.coordinatorlayout.widget.CoordinatorLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.material.appbar.AppBarLayout
android:id="@+id/appBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/white">
<com.google.android.material.appbar.CollapsingToolbarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fitsSystemWindows="true"
app:layout_scrollFlags="scroll|snap">
<androidx.appcompat.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="@dimen/padding_small"
android:paddingRight="@dimen/padding_small">
<ImageView
android:id="@+id/profileButton"
android:layout_width="@dimen/toolbar_button_dimen"
android:layout_height="@dimen/toolbar_button_dimen"
android:layout_gravity="start"
android:contentDescription="@string/profile_content_description"
android:src="@drawable/ic_astronaut_color_accent_24dp"
app:layout_constraintLeft_toLeftOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.appcompat.widget.Toolbar>
<FrameLayout
android:id="@+id/priceContainer"
android:name="app.carpecoin.PriceDataFragment"
android:layout_width="match_parent"
android:layout_height="@dimen/price_graph_height"
app:layout_collapseMode="parallax"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</com.google.android.material.appbar.CollapsingToolbarLayout>
</com.google.android.material.appbar.AppBarLayout>
<FrameLayout
android:id="@+id/contentContainer"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />
<androidx.constraintlayout.widget.ConstraintLayout
android:id="@+id/bottomSheet"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/margin_large"
app:layout_behavior="com.google.android.material.bottomsheet.BottomSheetBehavior">
<ImageView
android:id="@+id/bottom_handle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/ic_bottom_sheet_handle"
android:contentDescription="@string/saved_bottomsheet_handle_content_description"
android:elevation="@dimen/bottom_sheet_elevation_height"
android:src="@drawable/ic_save_planet_dark_48dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/bottom_handle_elevation"
android:layout_width="0dp"
android:layout_height="@dimen/bottom_sheet_elevation_height"
android:background="@color/bottom_sheet_handle_elevation"
android:contentDescription="@string/saved_bottomsheet_handle_content_description"
app:layout_constraintBottom_toBottomOf="@id/bottom_handle"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent" />
<FrameLayout
android:id="@+id/savedContentContainer"
android:layout_width="match_parent"
android:layout_height="0dp"
android:background="@android:color/white"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toBottomOf="@id/bottom_handle_elevation" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.coordinatorlayout.widget.CoordinatorLayout>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
fragment_content.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="viewmodel"
type="app.coinverse.content.ContentViewModel" />
</data>
<androidx.coordinatorlayout.widget.CoordinatorLayout
android:id="@+id/contentFragment"
android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<include
android:id="@+id/actionbar"
layout="@layout/toolbar"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/contentRecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/actionbar" />
<include
android:id="@+id/emptyContent"
layout="@layout/empty_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/actionbar" />
</RelativeLayout
</androidx.coordinatorlayout.widget.CoordinatorLayout>
</layout>
As a workaround for saving the RecyclerView state, the position can be saved in the instance state.
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
if (contentRecyclerView != null)
when (feedType) {
MAIN.name, DISMISSED.name ->
outState.putParcelable(CONTENT_RECYCLER_VIEW_STATE,
contentRecyclerView.layoutManager!!.onSaveInstanceState())
SAVED.name ->
outState.putInt(CONTENT_RECYCLER_VIEW_POSITION,
(contentRecyclerView.layoutManager as LinearLayoutManager)
.findLastVisibleItemPosition())
}
}
override fun onViewStateRestored(savedInstanceState: Bundle?) {
super.onViewStateRestored(savedInstanceState)
if (savedInstanceState != null)
when (feedType) {
MAIN.name, DISMISSED.name -> savedRecyclerLayoutState = savedInstanceState.getParcelable(CONTENT_RECYCLER_VIEW_STATE)
SAVED.name -> savedRecyclerPosition = savedInstanceState.getInt(CONTENT_RECYCLER_VIEW_POSITION)
}
}
To make sure the saved index is not out of bounds a check is required. Also, since RecyclerView item's are dismissed it is important to clear the saved index position so that the RecyclerView is not updated after an item is dismissed since this code snippet is contained in a LiveData observer.
if (feedType == SAVED.name && savedRecyclerPosition != 0) {
val position: Int =
if (savedRecyclerPosition >= adapter.itemCount) adapter.itemCount - 1
else savedRecyclerPosition
contentRecyclerView.layoutManager?.scrollToPosition(position)
savedRecyclerPosition = 0
}