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android - Creating and using ViewBinder inside a RecyclerView adapter

In my app, there is an Activity which has a RecyclerView inside, which loads the list of options needed for that screen.
In the code below, i tried to implement a binder, which is needed because of the recent Android changes.
However, when i open the activity starts, the application crashes, throwing this error, linking the line with binding = ItemSettingsBinding.bind(binding.root):
kotlin.UninitializedPropertyAccessException: lateinit property binding has not been initialized
What am i doing wrong? What's the correct way to implement a binder inside an adapter?
AdapterSettings.kt
class AdapterSettings(
var settingsList: List<DataItemSettings>,
var listener: OnItemClickListener
) : RecyclerView.Adapter<AdapterSettings.SettingsViewHolder>() {
private lateinit var binding: ItemSettingsBinding
inner class SettingsViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {
init {
itemView.setOnClickListener(this)
}
override fun onClick(p0: View?) {
val position : Int = adapterPosition
if (position != RecyclerView.NO_POSITION) {
listener.OnItemClick(position)
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SettingsViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.item_settings, parent, false)
return SettingsViewHolder(view)
}
override fun getItemCount(): Int {
return settingsList.size
}
override fun onBindViewHolder(holder: SettingsViewHolder, position: Int) {
binding = ItemSettingsBinding.bind(binding.root)
holder.itemView.apply {
binding.rvTitle.text = settingsList[position].stringTitle
binding.rvDescription.text = settingsList[position].stringDescription
binding.rvIcon.setImageResource(settingsList[position].itemIcon)
}
}
interface OnItemClickListener {
fun OnItemClick(position: Int)
}
}

I believe you're missing your inflate in onCreateViewHolder:
// Pseudo-Code
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SettingsViewHolder {
val binding = ItemSettingsBinding
.inflate(LayoutInflater.from(parent.context), parent, false)
return SettingsViewHolder(binding)
}
Then you can make use of it.

Create the binding in onCreateViewHolder and pass the binding into the ViewHolder instead of the inflated View. Thus you create a binding for each created view and only need to do the apply stuff in the onBindViewHolder
Example:
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SettingsViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.item_settings, parent, false)
val binding = ItemSettingsBinding.bind(view)
return SettingsViewHolder(binding)
}
override fun onBindViewHolder(holder: SettingsViewHolder, position: Int) {
holder.binding.apply {
rvTitle.text = settingsList[position].stringTitle
rvDescription.text = settingsList[position].stringDescription
rvIcon.setImageResource(settingsList[position].itemIcon)
}
}
Adapt your ViewHolder accordingly

There is indeed another way to ViewBind in an adapter.
First, we need to setup the ViewHolder in a different way:
inner class SettingsViewHolder(private val binding: ItemSettingsBinding):
RecyclerView.ViewHolder(binding.root), View.OnClickListener {
With this, we created a binding value inside the brackets, so we are able to call the items of the actual view or layout trough binding.root
Inside the viewholder, we need to create a function used to bind our items. We can either bind like this:
fun bind(item: Item) {
binding.item = item
binding.executePendingBindings()
}
Or like this:
fun bind(item: DataItemSettings) {
binding.rvTitle.text = settingsList[position].stringTitle
binding.rvDescription.text = settingsList[position].stringDescription
binding.rvIcon.setImageResource(settingsList[position].itemIcon)
}
NOTICE: 'getter for position: Int' is deprecated. Deprecated in Java.
And, final step, we need to write this, inside bindViewHolder:
override fun onBindViewHolder(holder: SettingsViewHolder, position: Int) {
holder.bind(settingsList[position])
}

How to add onClickListener to the items of the recyclerView in Kotlin?

I am using recyclerView to show data from firebase database and I want to handle clicks,
Now the important part is that I want to know the number that was clicked in order to test google play in app billing before showing the next activity
I mean user should click item number one then pay to see information number 1 and so on
Any help, please ?
//my adapter
class MyAdapter(
private val arrayList: ArrayList<Long>
) :
RecyclerView.Adapter<MyAdapter.MyViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val view =
LayoutInflater.from(parent.context)
.inflate(R.layout.layout_item, parent, false)
return MyViewHolder(view)
}
override fun getItemCount() = arrayList.size
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
holder.number.text = arrayList[position].toString()
}
class MyViewHolder(view: View) :
RecyclerView.ViewHolder(view) {
val number = view.findViewById<View>(R.id.singleNumberId) as TextView
}
}

Here is a small example I have of registering a click for a RecyclerView adapter item:
class PatientListAdapter : ListAdapter<Patient, PatientListAdapter.PatientViewHolder>(co.za.abcdefgh.viewmodels.PatientListViewModel.DiffItemCallback) {
// this property will be used to set the onclick callback for the entire adpater
var onPatientSelectedCallback: PatientSelectedCallback? = null
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): PatientViewHolder {
val view = LayoutInflater.from(parent.context)
.inflate(R.layout.item_patient, parent, false) as View
return PatientViewHolder(view)
}
override fun onBindViewHolder(holder: PatientViewHolder, position: Int) {
holder.view.item_patient_name.text = getItem(position).toString()
holder.view.item_patient_folderNumber.text = getItem(position).folderNumber
// lets set our on click for each viewholder here
holder.view.item_patient_info_card.setOnClickListener {
// the secret sauce .... getItem(holder.adapterPosition)
onPatientSelectedCallback?.onPatientSelected(getItem(holder.adapterPosition))
}
}
class PatientViewHolder(val view: View) : RecyclerView.ViewHolder(view)
// interface which defines a method signature that will called when a item in the adpater is selected
interface PatientSelectedCallback {
fun onPatientSelected(patient: Patient)
}
}
and then wherever you use the adapter after instantiating simply do:
val viewAdapter = PatientListAdapter()
viewAdapter.onPatientSelectedCallback =
object : PatientListAdapter.PatientSelectedCallback {
override fun onPatientSelected(patient: Patient) {
// do something with the chosen item
patientViewModel.setPatient(patient)
}
}

Kotlin: Passing data/array from Recyclerview Activity to Adapter

I am trying to pass an array from my Recyclerview Activity to its Adapter as such:
//Setting NavBar Title
val navBarTitle = intent.getStringExtra(FirstCustomViewHolder.LESSON_TITLE_KEY)
supportActionBar?.title = navBarTitle
var content : Array<String>
if (navBarTitle == "Introduction"){
content = arrayOf("Intro1", "Intro2")
}
else{
content = arrayOf(":esson1-1", "Lesson 1-2")
}
I am passing the array as such:
recyclerView_main.adapter = SecondAdapter(content)
And I am getting an angry red underline as shown below.
On mouse-over the pop-up error reads:
Too many arguments for public constructor......
Is there a proper way to pass an array or variable to my adapter? I am fairly new to Kotlin and appreciate and pointers.
Thank you.
Edit:
As requested, this is my adapter class:
class SecondAdapter : RecyclerView.Adapter<SecondCustomViewGolder>(){
//Variable below to be replaced by array from Activity
var lessons = arrayOf("Satu", "Dua", "Tiga", "Empat", "Lima", "Enam", "Tujuh",
"Lapan", "Sembilan")
override fun getItemCount(): Int {
return lessons.size
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SecondCustomViewGolder {
var layoutInflater = LayoutInflater.from(parent.context)
var cellForRow = layoutInflater.inflate(R.layout.lesson_row, parent, false)
return SecondCustomViewGolder(cellForRow)
}
override fun onBindViewHolder(holder: SecondCustomViewGolder, position: Int) {
}
}
class SecondCustomViewGolder(var viewTwo : View) : RecyclerView.ViewHolder(viewTwo){
}

Does your SecondAdapter class constructor accept an Array as an argument? If not, you must add it there. The error is because you're trying to pass an argument to a constructor that accepts no arguments.
EDIT
Do it like so:
class SecondAdapter(val lessonArray: Array<String>) : RecyclerView.Adapter<SecondCustomViewGolder>(){
override fun getItemCount(): Int {
return lessons.size
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SecondCustomViewGolder {
var layoutInflater = LayoutInflater.from(parent.context)
var cellForRow = layoutInflater.inflate(R.layout.lesson_row, parent, false)
return SecondCustomViewGolder(cellForRow)
}
override fun onBindViewHolder(holder: SecondCustomViewGolder, position: Int) {
}
}
class SecondCustomViewGolder(var viewTwo : View) : RecyclerView.ViewHolder(viewTwo){
}
I made it a val since it's my preference. If you intend to modify the variable, than you just declare it as a var in the constructor. There's no need to assign it inside the class. Just declaring it in the constructor makes it accessible throughout the class.

You can use the ListAdapter
and use submitList()

(Kotlin) Position of RecyclerView returns -1 when trying to click on an item

I'm new to Android development (and Kotlin).
I'm trying to implement a RecyclerView (which works fine) and when I click on a specific row it opens a new activity (Intent).
However, whenever I've press/click on one of the rows, I'm only able to get the value "-1" returned.
I've tried a number of different approaches (you should see the number of tabs in my browser).
This seems like it should be a fairly straightforward occurrence for something as common as a RecyclerView, but for whatever reason I'm unable to get it working.
Here is my RecyclerView Adapter file:
class PNHLePlayerAdapter (val players : ArrayList<PNHLePlayer>, val context: Context) : RecyclerView.Adapter<ViewHolder>() {
var onItemClick: ((Int)->Unit) = {}
// Gets the number of items in the list
override fun getItemCount(): Int {
return players.size
}
// Inflates the item views
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val itemView = LayoutInflater.from(context).inflate(
R.layout.pnhle_list_item,
parent,
false
)
val viewHolder = ViewHolder(itemView)
itemView.setOnClickListener {
onItemClick(viewHolder.adapterPosition)
}
return ViewHolder(itemView)
}
// Binds each item in the ArrayList to a view
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.tvPlayerName?.text = players[position].Name
holder.tvPlayerRank?.text = position.toString()
holder.tvPNHLe?.text = players[position].PNHLe.toString()
holder.tvTeam?.text = players[position].Team
holder.ivLeague?.setImageResource(leagueImageID)
}
}
class ViewHolder (view: View) : RecyclerView.ViewHolder(view) {
val linLayout = view.hor1LinearLayout
val ivTeam = view.teamImageView
val tvPlayerName = view.playerNameTextView
val tvPlayerRank = view.rankNumTextView
val tvPNHLe = view.pnhleTextView
val tvTeam = view.teamTextView
val ivLeague = view.leagueImageView
}
As you can see, there is a class property "onItemClick" which uses a lambda as the click callback.
I setOnClickListener in the onCreateViewHolder method after the view is inflated.
Next, in my Activity I add the list to my Adapter and set the call back.
However, every time I 'Toast' the position it is displayed as '-1'.
val adapter = PNHLePlayerAdapter(list, this)
adapter.onItemClick = { position ->
Toast.makeText(this, position.toString(),Toast.LENGTH_SHORT).show()
var intent = Intent(this, PlayerCardActivity::class.java)
//startActivity(intent)
}
rv_player_list.adapter = adapter
Perhaps I'm not thinking about this properly, but shouldn't the position represent the row number of the item out of the RecyclerView???
Ideally, I need to use the position so that I can obtain the correct item from the 'list' (ArrayList) so that I can pass information to my next Activity using the Intent

I found the issue.
Change this line in onCreateViewHolder:
return ViewHolder(itemView)
to this one:
return viewHolder

I would reorganize the adapter like this:
class PNHLePlayerAdapter : androidx.recyclerview.widget.RecyclerView.Adapter<Adapter.ViewHolder>() {
interface AdapterListener {
fun onItemSelected(position: Int?)
}
var players: List<Player> = listOf()
set(value) {
field = value
this.notifyDataSetChanged()
}
var listener: AdapterListener? = null
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent.context)
.inflate(R.layout.item_car_selector, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(position)
}
override fun getItemCount(): Int {
return brands.size
}
inner class ViewHolder(view: View): androidx.recyclerview.widget.RecyclerView.ViewHolder(view) {
private var position: Int? = null
private val baseView: LinearLayout? = view.findViewById(R.id.baseView) as LinearLayout?
...
init {
baseView?.setOnClickListener {
listener?.onManufacturerSelected(position)
}
}
fun bind(position: Int) {
this.position = position
...
}
}
}
And from your activity/fragment set the listener as adapter.listener = this, and implement the onItemSelected(position: Int?)
override fun onItemSelected(position: Int?) {
...
}

onBindViewHolder not called when use data binding on RecyclerView

onBindViewHolder not called when use data binding on Recyclerview.
So, the Activity show blank white screen.
When I see on logcat, the list size and itemCount is 20 but onBindViewHolder method never called.
class NewsAdapter : RecyclerView.Adapter<NewsAdapter.ViewHolder>() {
private val listArticle = mutableListOf<Article>()
fun update(list: List<Article>) {
listArticle.addAll(list)
notifyDataSetChanged()
}
override fun onCreateViewHolder(viewGroup: ViewGroup, viewType: Int): NewsAdapter.ViewHolder {
return ViewHolder(viewGroup)
}
class ViewHolder(
private val parent: ViewGroup,
private val binding: AdapterNewsBinding = DataBindingUtil.inflate(
LayoutInflater.from(parent.context),
R.layout.adapter_news,
parent,
false
)
) : RecyclerView.ViewHolder(binding.root) {
fun bind(article: Article) {
binding.article = article
}
}
override fun onBindViewHolder(viewHolder: ViewHolder, position: Int) {
Log.d("NewsAdapter", "onBindViewHolder")
viewHolder.bind(listArticle[position])
}
override fun getItemCount() = listArticle.size
}
How to call onBindViewHolder in Recyclerview with data binding?
So I can show the data on Activity.

Solved
add apply plugin: 'kotlin-kapt' in your app gradle
So, you can make static method like this on your adapter
companion object {
#BindingAdapter("items")
#JvmStatic
fun RecyclerView.bindItems(items: List<Article>?) {
val adapter = adapter as NewsAdapter
if (!items.isNullOrEmpty()) adapter.update(items)
}
}
Done