Develop Reference

Kotlin callbacks OnClickListener from Recyclerview for multiple buttons

I'm really confused about how the Kotlin lambdas work, specifically with click listeners. I had something that was working to do a single ViewModel function in my MainFragment but now I want multiple buttons on my adapter that do different things. At first I thought I would just have to pass all the necessary information including IDs for the different buttons to the callback then do a switch statement in my main fragment that does the appropriate ViewModel functions. As soon as I changed my input parameters the adapter no longer accepted my OnClickListener argument.
First I'll show the old OnClickListener that was working.
ItemAdapter
class ItemAdapter(private val context: Context, private val onClickListener: OnClickListener) : ListAdapter<SongWithRatings, ItemAdapter.SongViewHolder>(SongsComparator())
{
lateinit var isVisible: BooleanArray
override fun onCurrentListChanged(
previousList: List<SongWithRatings>,
currentList: List<SongWithRatings>
) {
super.onCurrentListChanged(previousList, currentList)
if(previousList.size != currentList.size) {
isVisible = BooleanArray(itemCount)
isVisible.fill(element = false)
}
}
class SongViewHolder(view: View) : RecyclerView.ViewHolder(view) {
val textView: TextView = view.findViewById(R.id.item_title)
val textViewBpm: TextView = view.findViewById(R.id.bpm)
val lastPlayed: TextView = view.findViewById(R.id.lastPlayed)
//new rating code 11/27/2021
val ratingBar: SeekBar = view.findViewById(R.id.ratingBar)
val ratingLabel: TextView = view.findViewById(R.id.ratingLabel)
val button: Button = view.findViewById(R.id.submitRating)
//expandable view 3/27/2022
val titleView: LinearLayout = view.findViewById(R.id.titleView)
val expand: ConstraintLayout = view.findViewById(R.id.expand)
//fragment launch buttons
val moreButton: Button = view.findViewById(R.id.moreButton)
val rateButton: Button = view.findViewById(R.id.rateButton)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SongViewHolder {
// create a new view
val adapterLayout = LayoutInflater.from(parent.context)
.inflate(R.layout.list_item, parent, false)
return SongViewHolder(adapterLayout)
}
override fun onBindViewHolder(holder: SongViewHolder, position: Int) {
val item = getItem(position)
//temporary code for initial rating
val initialRating = item.recentPerformanceRating()
var newRating = 0
holder.textView.text = item.song.songTitle
holder.textViewBpm.text = context.resources.getString(R.string.BPM,item.song.bpm)
holder.ratingLabel.setBackgroundColor(getStatusColor(item.recentPerformanceRating()))
//holder.imageView.setImageResource(item.imageResourceID)
holder.ratingLabel.text = context.resources.getString(R.string.Rating, initialRating )
holder.lastPlayed.text = item.lastPlayedString()
//rating bar functionality
holder.ratingBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
override fun onProgressChanged(seekBar: SeekBar, rating: Int, fromUser: Boolean) {
holder.ratingLabel.text = context.resources.getString(R.string.Rating, rating)
newRating = rating
}
override fun onStartTrackingTouch(seekBar: SeekBar) {}
override fun onStopTrackingTouch(seekBar: SeekBar) {}
})
//Performance Rating button functionality
holder.button.setOnClickListener{
onClickListener.onClick(item.song.songTitle, newRating)
}
holder.moreButton.setOnClickListener { }
class OnClickListener(val clickListener: (songTitle: String, newRating: Int) -> Unit) {
fun onClick(songTitle: String,newRating: Int) = clickListener(songTitle, newRating)
}
}
From MainFragment
val recyclerView = view.findViewById<RecyclerView>(R.id.recycler_view)
val adapter = ItemAdapter(requireContext(),
ItemAdapter.OnClickListener { songTitle, newRating ->
songViewModel.insertRating( Rating(System.currentTimeMillis(),songTitle,songViewModel.artistName, newRating )) }
)
Like I said, this all worked fine until I tried to use the OnClickListener with a SongsWithRatings parameter.
Am I even close here or do I have to redo my whole interface between the adapter, fragment and ViewModel?

You just have to make use of Interface for the purpose of providing listeners to the Fragment .
Step 1: Create an Interface Class.
interface ItemClickListener{
//You can include the parameters into the functions which you wish to be associated with the button. Suppose I want Title on Click of more Button, then I will pass it as a parameter
fun onButtonClick(val item : SongsWithRating)
fun onMoreButtonClicked(val title : String)
}
Step 2 : Create a listener variable in your adapter and call the functions in the onClick function of the respective buttons
class ItemAdapter(private val context: Context) : ListAdapter<SongWithRatings, ItemAdapter.SongViewHolder>(SongsComparator())
{
var listener : ItemClickListener ?= null
override fun onBindViewHolder(holder: SongViewHolder, position: Int) {
val item = getItem(position)
//Calling buttonClick and passing the function defined in the interface
along with the parameters
holder.button.setOnClickListener{
listener?.onButtonClick(item)
}
//Similarly for morebutton
holder.moreButton.SetOnClickListener{
listener?.onMoreButtonClicked(item.song.songTitle)
}
}
}
Step 3 : Now the final Step : Go to the fragment wherein the recyclerView is implemented
//Extent the Fragment with the Interface and override the methods
class Fragment : Fragment(), ItemClickListener{
//define Adapter and attach the listener
val adapter = ItemAdapter(requireContext()
adapter.listener = this
}
You are good to go

Kotlin Recyclerview ItemClick to new Intent

I have a problem. I can print a toast message when I click on any item in Recyclerview. But I want to switch to a different activity when clicked. Could you please help me in a very specific way? It is a very important project for me. The code blocks I wrote are as follows. Thanks in advance .
CustomersAdapter
class CustomersAdapter(private val companynameArray:ArrayList,private val companyoffArray:ArrayList, private val companyPhoneArray:ArrayList):
RecyclerView.Adapter<CustomersAdapter.CustomerHolder>() {
class CustomerHolder(view: View) : RecyclerView.ViewHolder(view) {
var recycleCompanyName: TextView?=null
var recycleOffName: TextView?=null
var recycleOffPhone: TextView?=null
init {
recycleCompanyName=view.findViewById(R.id.recycleCompanyName)
recycleOffName=view.findViewById(R.id.recycleOffName)
recycleOffPhone=view.findViewById(R.id.recycleOffPhone)
itemView.setOnClickListener {
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomerHolder {
val inflater= LayoutInflater.from(parent.context)
val view= inflater.inflate(R.layout.recycler_view_customer_row,parent,false)
return CustomersAdapter.CustomerHolder(view)
}
override fun getItemCount(): Int {
return companynameArray.size
}
override fun onBindViewHolder(holder: CustomerHolder, position: Int) {
holder.recycleCompanyName?.text="Şirket Adı:"+companynameArray[position]
holder.recycleOffName?.text="Şirket Yetkilisi :"+companyoffArray[position]
holder.recycleOffPhone?.text="İrtibat No : "+companyPhoneArray[position]
}
}
I did not specify the activity I want to go to. I would appreciate it if you could help as a method.
If it helps, I write the codes of the client class here.
class Customers : AppCompatActivity()
{
private lateinit var auth: FirebaseAuth
private lateinit var db: FirebaseFirestore
var companynameFB:ArrayList<String> = ArrayList()
var companyoffFB:ArrayList<String> = ArrayList()
var companyphoneFB:ArrayList<String> = ArrayList()
var adapter :CustomersAdapter?=null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_customers)
auth= FirebaseAuth.getInstance()
db= FirebaseFirestore.getInstance()
getDataFromFirestore()
var layoutManager= LinearLayoutManager(this)
recyclerView.layoutManager=layoutManager
adapter= CustomersAdapter(companynameFB,companyoffFB,companyphoneFB)
recyclerView.adapter=adapter
}
fun getDataFromFirestore(){
db.collection("Customers")
.addSnapshotListener { snapshot, exception ->
if(exception!=null){
Toast.makeText(applicationContext,exception.localizedMessage.toString(),Toast.LENGTH_LONG).show()
}else{
if(snapshot!=null){
if (!snapshot.isEmpty){
companynameFB.clear()
companyoffFB.clear()
companyphoneFB.clear()
val documents=snapshot.documents
for (document in documents){
val compname=document.get("compname") as String
val compoff=document.get("compoff") as String
val compphone=document.get("compphone") as String
val user=document.get("user") as String
val timeStamp=document.get("date") as Timestamp
val date=timeStamp.toDate()
companynameFB.add(compname)
companyoffFB.add(compoff)
companyphoneFB.add(compphone)
adapter!!.notifyDataSetChanged()
}
}
}
}
}
}
override fun onCreateOptionsMenu(menu: Menu?): Boolean {
val menuInflater=getMenuInflater()
menuInflater.inflate(R.menu.add_customer,menu)
return super.onCreateOptionsMenu(menu)
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
if(item.itemId==R.id.add){
val intent= Intent(this,AddCustomers::class.java)
intent.putExtra("info","new")
startActivity(intent)
}
return super.onOptionsItemSelected(item)
}

For starting a new Activity you need at least a context instance. And as is written in some other answers here, you could start the activity directly inside ViewHolder with View's context. But for better separations of responsibilities, I suggest you move your navigation to your Fragment/Activity, where all other navigations happen. That way you know at the look of Activity/Fragment, which navigations could be done from that screen, and you don't need to search for some hidden navigations that happen inside Adapter or ViewHolder. Also, if you need to perform startActivityForResult, then an instance of Context is not enough to do that. You need an Activity or Fragment instance for that and we have another reason to put all navigations there.
So you can do this like that:
ADD LAMBDA TO ADAPTER CONSTRUCTOR:
class CustomersAdapter(private val companynameArray: ArrayList,
private val companyoffArray: ArrayList,
private val companyPhoneArray: ArrayList,
private val onItemClick: () -> Unit) : RecyclerView.Adapter<CustomersAdapter.CustomerHolder>() {
NOTE: put lambda as the last constructor parameter.
ADD LAMBDA TO VIEWHOLDER CONSTRUCTOR:
class CustomerHolder(view: View,
private val onItemClick: () -> Unit) : RecyclerView.ViewHolder(view) {
MODIFY VIEWHOLDER CONSTRUCTOR CALL:
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomerHolder {
val inflater = LayoutInflater.from(parent.context)
val view = inflater.inflate(R.layout.recycler_view_customer_row,parent,false)
return CustomersAdapter.CustomerHolder(view, onItemClick) //Add onItemClick lambda instance from adapter here
}
INVOKE LAMBDA ON CLICK:
itemView.setOnClickListener {
onItemClick()
}
FIX ADAPTER CONSTRUCTOR CALL:
val adapter = CustomersAdapter(companynameArray, companyoffArray, companyPhoneArray) {
startActivity() // do your navigation here
}
Why did we place lambda as the last parameter of a constructor in our adapter? If the last parameter of a function is a function, then a lambda expression passed as the corresponding argument can be placed outside the parentheses(SOURCE). And we did exactly that with the last junk of code above where we handle our navigation.

put your click listener inside onBindViewHolder method
override fun onBindViewHolder(holder: CustomerHolder, position: Int) {
holder.recycleCompanyName?.text="Şirket Adı:"+companynameArray[position]
holder.recycleOffName?.text="Şirket Yetkilisi :"+companyoffArray[position]
holder.recycleOffPhone?.text="İrtibat No : "+companyPhoneArray[position]
holder.itemView.setOnClickListener {
// do what ever you want here
holder.itemView.context.startActivity( /*your intent here*/)
}
}
}

Step 1 : pass context here
class CustomersAdapter(val context:Context,private val
companynameArray:ArrayList,private val
companyoffArray:ArrayList, private val companyPhoneArray:ArrayList):
RecyclerView.Adapter<CustomersAdapter.CustomerHolder>() {
step 2:
itemView.setOnClickListener {
val intent=Intent(context,yourActivity::java.class)
startActivity(intent)
}

you need a context for intent so you can get it form the activity or fragment that are associated with this adapter and pass it to your intent or you can get it from any view in your inflated layout like this
val context=holder.title.context
val intent = Intent( context, EventDetail::class.java)
context.startActivity(intent)

Android - Store ArrayList persistent

My app is displaying a list of various categories (herbs, side dishes, ..) in a RecyclerView. Depending on the category you clicked on, a new Activity with a new RecylcerView opens containing all the ingredients.
Right now I have an ArrayList which gets filled with the ingredients via ".add" depending on the choosen category.
The problem im facing right now is, that I want to implement an option for the user to add own Ingredients. I tried storing the ArrayList containing the ingredients in SharedPreferences by using Gson, but I couldn't manage to add elements, since it always overwrote the current list.
What would be the best way to store the ingredients? A room, sqlite, ..?
Without further explanation, the ingredient list will only contain about 70 items max.
Thanks in advance.
Edit:
CatList.kt
class CatList : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_cat_list)
//Create List for categories
val cats = ArrayList<IngCat>()
//Fill categories
cats.add(IngCat(R.drawable.herbs, "Herbs"))
cats.add(IngCat(R.drawable.fluessiges, "Liquids"))
cats.add(IngCat(R.drawable.festes, "Solids"))
cats.add(IngCat(R.drawable.beilagen, "Sides"))
//Recyclerview
id_rv_CatList.layoutManager = LinearLayoutManager(this)
id_rv_CatList.adapter =
CatListAdapter(cats) {listItem, position -> //go to Ingredient List Activity
goToIngList(position, listItem.name)
}
//id_rv_CatList.addItemDecoration(DividerItemDecoration(this,DividerItemDecoration.HORIZONTAL))
//actionbar
val actionbar = supportActionBar
//set actionbar title
actionbar!!.title = "Ingredient - Categories"
}
private fun goToIngList(cat: Int, name: String){
val intent = Intent(this, IngList::class.java)
intent.putExtra("Category", cat)
intent.putExtra("Name", name)
startActivity(intent)
}
}
data class IngCat(var mImageResource:Int, var name:String)
IngList.kt
class IngList : AppCompatActivity() {
companion object {
var categoryChoosen : Int = 0
var catName : String = "Err"
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_ing_list)
//Initilize Ingredient List
val ings :ArrayList<IngIng> = ArrayList()
//Get category and category name
categoryChoosen = intent.getIntExtra("Kategorie",0)
catName = intent.getStringExtra("Name")!!
when (categoryChoosen) {
0 -> {
ings.add(IngIng("https://doeel.com/images/thumbnails/1100/900/detailed /92/Turmeric_Powder___Holud_Gura__.png", "Turmeric Powder"))
}
1 -> ings.add(IngIng("https://www.miraherba.de/4923-large_default/bio-ghee-300-g.jpg", "Ghee"))
2 -> ings.add(IngIng("https://www.organicfacts.net/wp-content/uploads/coriander-1.jpg", "Coriander leaves"))
3 -> ings.add(IngIng("https://gbc-cdn-public-media.azureedge.net/img75602.1426x713.jpg", "Potatoes"))
}
//Actionbar Settings
setSupportActionBar(toolbar)
val actionbar = supportActionBar
actionbar!!.title = "Ingredients- $catName"
actionbar.setDisplayHomeAsUpEnabled(true)
//Recyclerview
id_rv_IngList.layoutManager = GridLayoutManager(this,2)
id_rv_IngList.adapter =
IngListAdapter(ings) {//ClickListener RecyclerView
Toast.makeText(this, "Item clicked: ${it.name}", Toast.LENGTH_SHORT).show()
}
//Actionbar
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
// Inflate the menu; this adds items to the action bar if it is present.
menuInflater.inflate(R.menu.actionbar_ing_list, menu)
return true
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
return when (item.itemId) {
R.id.id_menu_action_add -> {
val intent = Intent(this, AddIngredient::class.java)
startActivity(intent)
true
}
else -> super.onOptionsItemSelected(item)
}
}
override fun onSupportNavigateUp(): Boolean {
onBackPressed()
return true
}
}
IngListAdapter.kt
class IngListAdapter (private val ings: ArrayList<IngIng>, val clickListener: (IngIng)->Unit): RecyclerView.Adapter<RecyclerView.ViewHolder>(){
override fun getItemCount(): Int = ings.size
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
val v: View = LayoutInflater.from(parent.context).inflate(R.layout.recyclerview_ing_list_item, parent, false)
return IngViewHolder(v)
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
var currentItem = ings.get(position)
when (holder) {
is IngViewHolder -> {
holder.tvIngList.text = currentItem.name
// holder.ivIngImage.setImageResource(currentItem.mImageResource)
Picasso.get().load(currentItem.mImageResource).placeholder(R.drawable.ic_broken_image_black_200dp).error(R.drawable.ic_broken_image_red_24dp).into(holder.ivIngImage)
holder.cvIngCard.setOnClickListener{
clickListener(currentItem)
}
}
}
}
}
class IngViewHolder (view: View) : RecyclerView.ViewHolder(view) {
val tvIngList: TextView = view.id_text_ing
val ivIngImage: ImageView = view.id_img_ing
val cvIngCard: MaterialCardView = view.id_cv_ing_list
}

I personally think Json/Gson in a SharedPreference is the easiest way to go if there are so few items. The way I would handle it is to store the list in memory at application startup, and persist the list back to the SharedPreference when the app is shut down. Also when the app gets stopped for good measure because you can't 100% be sure onDestroy will be called.
So first I'd make a class to store the data. If you were using Fragments that all are in the same Activity, you'd put this in a ViewModel. But since they are separate Activities, you need a singleton for them. (Google doesn't recommend using multiple Activities because it's hard to share data between them. But it's not impossible. It's what we did before Fragments.)
To do it as a singleton, you could have a class like this:
class IngredientsRepo private constructor (application: Application) {
companion object {
private val INSTANCE: IngredientsRepo? = null
fun getInstance(application: Application) =
INSTANCE ?: IngredientsRepo(application).also { INSTANCE = it }
private const KEY_JSON_PREF = "ingredientsJson"
}
private val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(application)
val herbsList: MutableList<IngCat>
val liquidsList: MutableList<IngCat>
val solidsList: MutableList<IngCat>
val sidesList: MutableList<IngCat>
init {
val json = sharedPreferences.getString(KEY_JSON_PREF, null)
if (json == null) {
// initialize your list contents for the first time
} else {
// convert your json and fill the data into your lists
}
}
fun save {
val jsonString = // Convert your lists to Json
sharedPreferences.edit().putString(KEY_JSON_PREF, jsonString).apply()
}
}
This class becomes responsible for setting up your lists. You can retrieve it from any Activity with IngredientsRepo.getInstance(this) and you can add and remove items from the lists whenever you like. You can also call save on it whenever you like to persist the latest data. It's probably sufficient to do this in onStop() of any Activity that modifies the list.
More properly, the data in this class would only be exposed with immutable lists, and you'd add functions for adding and removing items, so only this class directly modifies the lists. I didn't want to overcomplicate the example, but it would be better for encapsulation to not have Activities (which are supposed to be pure UI components) directly modifying data structures.

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

in kotlin how to set click event for recyclerview adapter

I am new on kotlin android. I have created the adapter for recyclerview. But I am not able to perform a click event for each recyclerview item. I need the explanation with the reference code.
Kindly help me to do this.
Thanks in advance.
Here is my code for your reference.
class CustomAdapter(val readerList: ReaderResponse, mainActivity:
MainActivity,val btnlistener: BtnClickListener) :
RecyclerView.Adapter<CustomAdapter.ViewHolder>() {
companion object {
var mClickListener: BtnClickListener? = null
}
override fun onCreateViewHolder(viewgroup: ViewGroup, index: Int): ViewHolder
{
val view=LayoutInflater.from(viewgroup?.context).inflate(R.layout.reader_list,viewgroup,false)
return ViewHolder(view)
}
override fun getItemCount(): Int {
return readerList.results.size
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
mClickListener = btnlistener
val item = readerList
val reader:ReaderData = readerList.results[position]
/*p0?.imageview?.text=reader.readerIcon*/
holder?.reader_status?.text=reader.readerStatus
holder?.ward_name?.text=reader.wardName
holder?.reader_id?.text=reader.readerID
holder?.reader_name?.text=reader.readerName
holder?.reader_location?.text=reader.readerLocation
if (reader.readerStatus.toLowerCase().equals("yes")){
holder.reader_name.setTextColor(Color.parseColor("#24a314"))
}else if (reader.readerStatus.toLowerCase().equals("no")){
holder.reader_name.setTextColor(Color.parseColor("#f4312d"))
holder.warning.setVisibility(View.VISIBLE)
}
}
class ViewHolder(itemView: View) :RecyclerView.ViewHolder(itemView) {
val imageview = itemView.findViewById(R.id.imageview) as Button
val reader_name = itemView.findViewById(R.id.reader_name) as TextView
val reader_location = itemView.findViewById(R.id.floor_no) as TextView
val ward_name = itemView.findViewById(R.id.ward_name) as TextView
val reader_id = itemView.findViewById(R.id.reader_id) as TextView
val reader_status = itemView.findViewById(R.id.reader_status) as TextView
val warning=itemView.findViewById(R.id.warning) as Button
}
open interface BtnClickListener {
fun onBtnClick(position: Int)
}
}

You could use the following approach. This is taken from this blog by Antonio Leiva
Assuming your data class is ReaderData
class CustomAdapter(val readers: List, val listener: (ReaderData) -> Unit) {
/* Other methods */
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
/*...*/
holder.imageview.setOnClickListener {
listener(readers[position])
}
}
}
Now in your Activity or Fragment
recyclerview.adapter = CustomAdapter(readersList) { readerData ->
Log.i(TAG, "${readerData.readerID} clicked")
}
The idea is you pass a lambda which will be executed when your desired item is clicked.

You just need to implement BtnClickListener in the corresponding Activity in which this adapter is initialized. Once you have implemented the BtnClickListener it would override the function onBtnClick in the activity.
The only thing you need to do in the adapter is to initialize the onClickListener on the element you need and in that method just call imageview.setOnClickListener { mClickListener?.onBtnClick(position) }. It would send the position back in activity and you can perform your specific task there. For example I have implemented the ClickListener in one Activity and printed the log there it works fine. Below is the demo code for it.
class Main2Activity : AppCompatActivity(), CustomAdapter.BtnClickListener {
override fun onBtnClick(position: Int) {
Log.d("Position", position.toString())
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main2)
recyclerView.layoutManager = LinearLayoutManager(this, LinearLayout.VERTICAL, false)
val readerResponseList = ArrayList<YourModelClassName>()
val adapter = CustomAdapter(readerResponseList,this,this)
recyclerView.adapter = adapter
}
Hope it Helps.