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RecyclerView with databinding and onClick listener

I'm starting using Kotlin (i'm a web dev) to maintain the mobile app of my current job. To practice my learning, I'm creating a basic app which is displaying a list of France departments (using a REST Api), and I need to allow the user to click on a list item to get more info on the selected item.
I'm trying to build this with databinding, Koin as dependency injection, and Room as db layer.
My issue is that I created a RecyclerView custom Adapter, and used the databinding to give it the datas. But now I want to implement the onClick behaviour, which should launch another activity to display item details. My problem is: I don't know how to do this in a clean way.
I was thinking about creating a viewModel to link to my Adapter, but can't really find how to do it well. And even if I did, how to start another activity in a viewModel ? (don't have access to the context and startActivity function). So I finally dropped that solution that doesn't seems to fit.
So I'm currently thinking of passing directly from my adapter the onClick function, but can't find a way to bind this function in my xml file. Here is my files:
MainActivity:
class MainActivity : AppCompatActivity() {
private val mViewModel: DepartmentsViewModel by viewModel()
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.toolbar.title = "Liste des départements"
val adapter = DepartmentListAdaptater()
binding.recyclerview.adapter = adapter
binding.recyclerview.layoutManager = LinearLayoutManager(this)
mViewModel.allDepartments.observe(this, Observer { data -> adapter.submitList(data) })
}
}
RecyclerView.Adapter:
class DepartmentListAdaptater : RecyclerView.Adapter<DepartmentListAdaptater.ViewHolder>() {
private var dataSet: List<Department>? = null
inner class ViewHolder(private val binding: DepartmentListRowBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(department: Department?) {
binding.department = department
}
}
fun submitList(list: List<Department>) {
dataSet = list
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val binding = DepartmentListRowBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return ViewHolder(binding)
}
override fun getItemCount(): Int = dataSet?.size ?: 0
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(dataSet?.get(position))
}
}
The XML View:
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android">
<data>
<variable name="department" type="com.navalex.francemap.data.entity.Department" />
</data>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="72dp">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical"
android:background="#drawable/list_item_bg"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"
android:layout_alignParentBottom="true"
android:clickable="true"
tools:ignore="UselessParent">
<TextView
android:id="#+id/textView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:paddingRight="16dp"
android:text="#{department.nom}"
android:paddingLeft="16dp"/>
</LinearLayout>
</RelativeLayout>
</layout>

First I want to say that it's really impressive that you are a web developer and you already have a lot of knowledge about things like dependency injection and keep the state of the view on ViewModel, congrats. Now, let's talk about your problem... I'll start with some suggestions that will improve the code clarity and performance.
For the Adapter implementation, always prefer to use ListAdapter, because this implementation have a more efficient way to compare the current list with the new list and update it. You can follow this example:
class MyAdapter: ListAdapter<ItemModel, MyAdapter.MyViewHolder>(DIFF_CALLBACK) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val binding = FragmentFirstBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return MyViewHolder(binding)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
holder.bind(getItem(position))
}
class MyViewHolder(
private val binding: FragmentFirstBinding
): RecyclerView.ViewHolder(binding.root) {
fun bind(item: ItemModel) {
// Here you can get the item values to put this values on your view
}
}
companion object {
private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<ItemModel>() {
override fun areItemsTheSame(oldItem: ItemModel, newItem: ItemModel): Boolean {
// need a unique identifier to have sure they are the same item. could be a comparison of ids. In this case, that is just a list of strings just compare like this below
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: ItemModel, newItem: ItemModel): Boolean {
// compare the objects
return oldItem == newItem
}
}
}
}
In your fragment, you have a observer, that observe the value you want to sent to the adapter, right? When a update happen, you call the submitList sending the updated list and when the adapter receive this new list, the adapter will be responsible to update just the items that changed, because of your DIFF_CALLBACK implementation.
About the onClick item, you can wait for a callback on your adapter. Doing this:
class MyAdapter(
private val onItemClicked: (item: ItemModel) -> Unit
): ListAdapter<ItemModel, MyAdapter.MyViewHolder>(DIFF_CALLBACK) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val binding = FragmentFirstBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return MyViewHolder(binding, onItemClicked)
}
// ...
class MyViewHolder(
private val binding: FragmentFirstBinding,
private val onItemClicked: (item: ItemModel) -> Unit
): RecyclerView.ViewHolder(binding.root) {
fun bind(item: ItemModel) {
// ...
// Here you set the callback to a listener
binding.root.setOnClickListener {
onItemClicked.invoke(item)
}
}
}
// ...
}
As you can see, we will receive the callback on the Adapter constructor, then we send to the ViewHolder by constructor too. And on the ViewHolder bind we set the callback to a click listener.
On you fragment, you will have something like this:
class MyFragment: Fragment() {
private lateinit var adapter: MyAdapter
private val onItemClicked: (itemModel: ItemModel) -> Unit = { itemModel ->
// do something here when the item is clicked, like redirect to another activity
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
adapter = MyAdapter(onItemClicked)
}
}
I hope it helps you. Please, let me know if you need something more. I really appreciate helping.

I don't know about data binding specifically, but a typical way to do it is to let the Activity handle details like app navigation, and let the Adapter trigger that logic. A listener function is an easy way to do this:
// in your Adapter
var clickListener: ((YourData) -> ())? = null
// in your ViewHolder (make it an inner class so it can access the Adapter's
// fields, like the listener object and the stored data)
init {
clickableView.setOnClickListener {
// pass back whatever data here, if the listener needs to know
// what's been clicked. I'm just doing a lookup and passing
// the data item currently being displayed
clickListener?.invoke(
adapterData[bindingAdapterPosition]
)
}
}
// in your Activity, when setting up the adapter
adapter.clickListener = { whateverData ->
// do what you need to do in response to the click
}
So the Activity itself is defining that logic about actions that should be taken when a click happens - it's basically wiring up different parts of the app, so the Adapter doesn't need to be concerned with anything except taking data, displaying it, and informing a listener when specific interactions take place. That listener code (defined by the Activity) could navigate somewhere else, or update a database, or pass it to a networking component... the adapter doesn't need to know about that.
(The non-Kotlin way to do this would be to create an interface and have the Activity implement that, and pass itself as the listener/callback object, that kind of thing)

Traversing a LiveData List in the ViewModel

I'm a rookie Android developer, and could use a little guidance regarding traversing a LiveData List in the ViewModel.
I am basing my app on the MVVM design, and it is simply scanning folders for images, and adding some folders to a favourites list I store in a database. During the scans, I need to check with the stored favourites to see if any of the scanned folders are favourites.
It is the "check against the stored favourites" part that gives me trouble.
Here are the relevant bits from my fragment:
class FoldersFragment : Fragment(), KodeinAware {
override val kodein by kodein()
private val factory: FoldersViewModelFactory by instance()
private var _binding: FragmentFoldersBinding? = null
private val binding get() = _binding!!
private lateinit var viewModel: FoldersViewModel
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
_binding = FragmentFoldersBinding.inflate(inflater, container, false)
val root: View = binding.root
return root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(this, factory).get(FoldersViewModel::class.java)
binding.rvFolderList.layoutManager = GridLayoutManager(context, gridColumns)
val adapter = FolderItemAdapter(listOf(), viewModel)
binding.rvFolderList.adapter = adapter
viewModel.getFolderList().observe(viewLifecycleOwner, {
adapter.folderItems = it
binding.rvFolderList.adapter = adapter // Forces redrawing of the recyclerview
})
...
}
Now, that observer work just fine - it picks up changes and my RecyclerView responds with delight; all is well.
Here are the relevant bits from my RecyclerView adapter:
class FolderItemAdapter(var folderItems: List<FolderItem>, private val viewModel: FoldersViewModel):
RecyclerView.Adapter<FolderItemAdapter.FolderViewHolder>() {
private lateinit var binding: FolderItemBinding
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FolderViewHolder {
binding = FolderItemBinding.inflate(LayoutInflater.from(parent.context))
val view = binding.root
return FolderViewHolder(view)
}
override fun onBindViewHolder(holder: FolderViewHolder, position: Int) {
val currentItem = folderItems[position]
...
if (viewModel.isFavourite(currentItem)) {
// do stuff
}
...
}
}
And with that, my problem; the check viewModel.isFavourite(currentItem)always returns false.
The implementation in my ViewModel is:
class FoldersViewModel(private val repository: FoldersRepository) : ViewModel() {
fun getImageFolders() = repository.getImageFolders()
fun isFavourite(item: FolderItem): Boolean {
var retval = false
getImageFolders().value?.forEach {
if (it.path == item.path) {
retval = true
}
}
}
}
The `getImageFolders() function is straight from the repository, which again is straight from the Dao:
#Dao
interface FoldersDao {
#Query("SELECT * FROM image_folders")
fun getImageFolders(): LiveData<List<FolderItem>>
}
My problem is that I simply can't traverse that list of favourites in the ViewModel. The isFavourite(item: FolderItem) function always returns false because getImageFolders().value always is null. When I check getImageFolders() it is androidx.room.RoomTrackingLiveData#d0d6d31.
And the conundrum; the observer is doing the exact same thing? Or isn't it?
I suspect I am not understanding something basic here?

Your getImageFolders() function retrieves something asynchronously from the database, because you specified that it returns a LiveData. When you get the LiveData back, it will not immediately have a value available. That's why your .value?.forEach is never called. value is still null because you're trying to read it immediately. A LiveData is meant to be observed to obtain the value when it arrives.
There are multiple ways to make a DAO function return something without blocking the current thread. (Handy table here.) Returning a LiveData is one way, but it's pretty awkward to use if you only want one value back. Instead, you should use something from the One-shot read row in the linked table.
If you aren't using RxJava or Guava libraries, that leaves a Kotlin coroutines suspend function as the natural choice.
That would make your Dao look like:
#Dao
interface FoldersDao {
#Query("SELECT * FROM image_folders")
suspend fun getImageFolders(): List<FolderItem>
}
And then your ViewModel function would look like:
suspend fun isFavourite(item: FolderItem): Boolean {
return getImageFolders().any { it.path == item.path }
}
Note that since it is a suspend function, it can only be called from a coroutine. This is necessary to avoid blocking the main thread. If you're not ready to learn coroutines yet, you can replace this function with a callback type function like this:
fun isFavoriteAsync(item: FolderItem, callback: (Boolean)->Unit) {
viewModelScope.launch {
val isFavorite = getImageFolders().any { it.path == item.path }
callback(isFavorite)
}
}
and at the call site use it like
viewModel.isFavoriteAsync(myFolderItem) { isFavorite ->
// do something with return value when it's ready here
}

your getImageFolder() is an expensive function so
getImageFolders().value?.forEach {
if (it.path == item.path) {
retval = true
}
}
in this part the value is still null that is why it returns false.
the solution is to make sure the value is not null. Do not check null inside isFavorite function instead call isFavorite() function only when getImageFolder() is done the operation.
What you should do is something like this
observe the liveData of imageFolders
ondatachange check if the data is null or not
if it is not null update UI and use isFavourite() function

why flow collect call more than twice in kotlin?

Hey I am working in kotlin flow in android. I noticed that my kotlin flow collectLatest is calling twice and sometimes even more. I tried this answer but it didn't work for me. I printed the log inside my collectLatest function it print the log. I am adding the code
MainActivity.kt
class MainActivity : AppCompatActivity(), CustomManager {
private val viewModel by viewModels<ActivityViewModel>()
private lateinit var binding: ActivityMainBinding
private var time = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setupView()
}
private fun setupView() {
viewModel.fetchData()
lifecycleScope.launchWhenStarted {
repeatOnLifecycle(Lifecycle.State.STARTED) {
viewModel.conversationMutableStateFlow.collectLatest { data ->
Log.e("time", "${time++}")
....
}
}
}
}
}
ActivityViewModel.kt
class ActivityViewModel(app: Application) : AndroidViewModel(app) {
var conversationMutableStateFlow = MutableStateFlow<List<ConversationDate>>(emptyList())
fun fetchData() {
viewModelScope.launch {
val response = ApiInterface.create().getResponse()
conversationMutableStateFlow.value = response.items
}
}
.....
}
I don't understand why this is calling two times. I am attaching logs
2022-01-17 22:02:15.369 8248-8248/com.example.fragmentexample E/time: 0
2022-01-17 22:02:15.629 8248-8248/com.example.fragmentexample E/time: 1
As you can see it call two times. But I load more data than it call more than twice. I don't understand why it is calling more than once. Can someone please guide me what I am doing wrong. If you need whole code, I am adding my project link.

You are using a MutableStateFlow which derives from StateFlow, StateFlow has initial value, you are specifying it as an emptyList:
var conversationMutableStateFlow = MutableStateFlow<List<String>>(emptyList())
So the first time you get data in collectLatest block, it is an empty list. The second time it is a list from the response.
When you call collectLatest the conversationMutableStateFlow has only initial value, which is an empty list, that's why you are receiving it first.
You can change your StateFlow to SharedFlow, it doesn't have an initial value, so you will get only one call in collectLatest block. In ActivityViewModel class:
var conversationMutableStateFlow = MutableSharedFlow<List<String>>()
fun fetchData() {
viewModelScope.launch {
val response = ApiInterface.create().getResponse()
conversationMutableStateFlow.emit(response.items)
}
}
Or if you want to stick to StateFlow you can filter your data:
viewModel.conversationMutableStateFlow.filter { data ->
data.isNotEmpty()
}.collectLatest { data ->
// ...
}

The reason is collectLatest like backpressure. If you pass multiple items at once, flow will collect latest only, but if there are some time between emits, flow will collect each like latest
EDITED:
You really need read about MVVM architecture.
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setupView()
}
private fun setupView() {
if (supportFragmentManager.findFragmentById(R.id.fragmentView) != null)
return
supportFragmentManager
.beginTransaction()
.add(R.id.fragmentView, ConversationFragment())
.commit()
}
}
Delele ActivityViewModel and add that logic to FragmentViewModel.
Also notice you don't need use AndroidViewModel, if you can use plain ViewModel. Use AndroidViewModel only when you need access to Application or its Context

notifyDataSetChanged and toMutableList don 't Works (Kotlin)

I am getting data from API http and using dataBinding and viewModel, all works but when I try to convert my list to mutableList and add All don't getting nothing, also try pass the data of simple way and working , the data is be there, the problem is that notifyDataSetChanged() don't do changes in my Adapter and I dont see nathing in the recyclerView.
class MainActivity : AppCompatActivity() {
private lateinit var viewModel: MostPopularTVShowsViewModel
private lateinit var activityMainBinding : ActivityMainBinding
private var tvShows: List<TVShow> = ArrayList()
private lateinit var tvShowAdapter:TVShowsAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
activityMainBinding = DataBindingUtil.setContentView(this,R.layout.activity_main)
doInitialization()
}
private fun doInitialization(){
activityMainBinding.tvShowRecycleView.setHasFixedSize(true)
viewModel= ViewModelProvider(this).get(MostPopularTVShowsViewModel::class.java)
tvShowAdapter= TVShowsAdapter(tvShows)
activityMainBinding.tvShowRecycleView.adapter=tvShowAdapter
getMostPopularTVShows()
}
private fun getMostPopularTVShows(){
activityMainBinding.isLoading=true
viewModel.getMostPopularTVShows(0).observe(this, { mostPopularTVShowsResponse ->
activityMainBinding.isLoading=false
if (mostPopularTVShowsResponse != null){
tvShows.toMutableList().addAll(mostPopularTVShowsResponse.tvShows)
//tvShows=mostPopularTVShowsResponse.tvShows
println("size is: "+tvShows.size)
tvShowAdapter.notifyDataSetChanged()
}else{
Toast.makeText(this," NULL", Toast.LENGTH_SHORT).show()
}
})
}
}
when i change tvShows=mostPopularTVShowsResponse.tvShows insted tvShows.toMutableList().addAll(mostPopularTVShowsResponse.tvShows) the list gets the data but notifyDataSetChanged dont working
this is my adapter
class TVShowsAdapter(private val items: List<TVShow>): RecyclerView.Adapter<TVShowsAdapter.ViewHolder>(){
private lateinit var layoutInflater: LayoutInflater
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
layoutInflater= LayoutInflater.from(parent.context)
val binding: ItemContainerTvShowBinding = DataBindingUtil.inflate(
layoutInflater, R.layout.item_container_tv_show,parent,false)
return ViewHolder(binding)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int)= holder.bind(items[position])
override fun getItemCount()= items.size
class ViewHolder(private val itemContainerTvShowBinding: ItemContainerTvShowBinding):
RecyclerView.ViewHolder(itemContainerTvShowBinding.root){
fun bind (tvShow: TVShow){
itemContainerTvShowBinding.tvShow=tvShow
itemContainerTvShowBinding.executePendingBindings()
}
}
}

You're not actually changing the data in the adapter. You're passing in a reference to the tvShows ArrayList when you create the adapter, so if you changed the contents of that list the adapter would be able to see it. But when you do
tvShows.toMutableList().addAll(mostPopularTVShowsResponse.tvShows)
you're creating a new, separate list by calling toMutableList, and you're adding stuff to that. tvShows is still the original, immutable ArrayList with nothing in it.
If you're going to do it this way, you need to make the list mutable from the beginning
val tvShows = mutableListOf<TVShow>()
then you can clear and add to it when you get new data.
Generally though, a better idea is to give the adapter some kind of setData function where you pass in a list, so it can update its own internal data set and notify itself about the change. That way the adapter manages it state itself, all your activity or fragment needs to do is pass it some new data

Saving the instance of Recycler view during orientation change

I have a RecyclerView which was build using an Arraylist. That Arraylist consists of User defined objects named ListItem.
Each recyclerview has a card view. Each CardView holds each ListItem.
I have removed one CardView from that RecyclerView.
When I rotate the screen , A new Activity is created which results in showing the old data. But I want the recyclerview to hold only updated list and should retain the scrolled position.
ListItem class :
class ListItem(var title: String, var info: String, val imageResource: Int) {
}
MainActivity class :
class MainActivity : AppCompatActivity() {
private lateinit var mSportsData: ArrayList<ListItem>
private lateinit var mAdapter: MyAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val gridColumnCount = resources.getInteger(R.integer.grid_column_count)
recycler_view.layoutManager = GridLayoutManager(this,gridColumnCount)
mSportsData = ArrayList()
recycler_view.setHasFixedSize(true)
initializeData()
recycler_view.adapter = mAdapter
var swipeDirs = 0
if (gridColumnCount <= 1) {
swipeDirs = ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT
}
val helper = ItemTouchHelper(object : ItemTouchHelper.SimpleCallback(ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT or ItemTouchHelper.UP or ItemTouchHelper.DOWN,swipeDirs) {
override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
val from = viewHolder.adapterPosition
val to = target.adapterPosition
Collections.swap(mSportsData,from,to)
mAdapter.notifyItemMoved(from,to)
return true
}
override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
mSportsData.removeAt(viewHolder.adapterPosition)
mAdapter.notifyItemRemoved(viewHolder.adapterPosition)
}
})
helper.attachToRecyclerView(recycler_view)
}
private fun initializeData() {
val sportsList : Array<String> = resources.getStringArray(R.array.sports_titles)
Log.d("Printing","$sportsList")
val sportsInfo : Array<String> = resources.getStringArray(R.array.sports_info)
val sportsImageResources : TypedArray = resources.obtainTypedArray(R.array.sports_images)
mSportsData.clear()
for (i in sportsList.indices-1) {
Log.d("Printing","${sportsList[i]},${sportsInfo[i]},${sportsImageResources.getResourceId(i,0)}")
mSportsData.add(ListItem(sportsList[i], sportsInfo[i], sportsImageResources.getResourceId(i, 0)))
}
sportsImageResources.recycle()
mAdapter = MyAdapter(mSportsData,this)
mAdapter.notifyDataSetChanged()
}
fun resetSports(view: View) {
initializeData()
}
}
MyAdapter class :
class MyAdapter(var mSportsData: ArrayList<ListItem>, var context: Context) : RecyclerView.Adapter<MyAdapter.ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(LayoutInflater.from(context).inflate(R.layout.wordlist_item,parent,false))
}
override fun getItemCount() = mSportsData.size
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val listItem = mSportsData.get(position)
holder.bindTo(listItem)
}
inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {
init {
itemView.setOnClickListener(this)
}
override fun onClick(view: View) {
val currentSport = mSportsData.get(adapterPosition)
val detailIntent = Intent(context, DetailActivity::class.java)
detailIntent.putExtra("title", currentSport.title)
detailIntent.putExtra("image_resource", currentSport.imageResource)
context.startActivity(detailIntent)
}
fun bindTo(currentSport : ListItem){
itemView.heading_textview.setText(currentSport.title)
itemView.description_textview.setText(currentSport.info)
Glide.with(context).load(currentSport.imageResource).into(itemView.image_view)
}
}
}

You can restrict activity restarting in your Manifest if you have same layout for Portrait and Landscape mode.
Add this to your activity in the manifest.
<activity android:name=".activity.YourActivity"
android:label="#string/app_name"
android:configChanges="orientation|screenSize"/>
If you don't want to restrict screen orientation changes, then you can use OnSaveInstanceState method to save your older data when orientation changed. Whatever data you save via this method you will receive it in your OnCreate Method in bundle. Here is the helping link. So here as you have ArrayList of your own class type you also need to use Serializable or Parcelable to put your ArrayList in your Bundle.
Except these making ArrayList as public static is always a solution, But its not a good solution in Object Oriented paratime. It can also give you NullPointerException or loss of data, in case of low memory conditions.

It looks like initializeData is called twice since onCreate is called again on orientation change, you could use some boolean to check if data has been already initialized then skip initializing

What you are doing is you are deleting the values that are passed down to the recyclerview but when the orientation changes the recyclerview reloads from activity and the original data from activity is passed down again and nothing changes, so if you want to save the changes in recyclerview you have to change the original data in the activity so that if the view reloads the data is the same.

I think u initialize adapter in oncreate method in which the whole adapter will be recreated and all datas is also newly created when configuration changes. Because u init data in oncreate method. Try something globally maintain the list and also delete the item in the list in activity when u delete in adapter also. Or try something like view model architecture

Use MVVM pattern in the project. It will manage the orientation state.
MVVM RecyclerView example:
https://medium.com/#Varnit/android-data-binding-with-recycler-views-and-mvvm-a-clean-coding-approach-c5eaf3cf3d72