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How can i add empty constructor to RecyclerView Adapter android kotlin

I need to add empty constructor to my Adapter, but i have already primary constructor.
My code:
class RvStatesAdapter(private var stateList: List<State>): RecyclerView.Adapter<RvStatesAdapter.MyViewHolder>() {
inner class MyViewHolder(val binding: RvStateListBinding): RecyclerView.ViewHolder(binding.root)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
return MyViewHolder(RvStateListBinding.inflate(LayoutInflater.from(parent.context), parent, false))
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
}
override fun getItemCount(): Int {
return stateList.size
}
I have tried to use costructor(): this() but in this case i dont understand what i need to put in this() brackets

You can make Adapter constructor without params by instead of passing list in primary constructor use function to submit list in adapter.
class RvStatesAdapter(): RecyclerView.Adapter<RvStatesAdapter.MyViewHolder>() {
private val stateList: ArrayList<State> = ArrayList<State>()
/**
* submit list to recycler view adapter for populating items
*/
fun submitList(list: List<State>) {
stateList.addAll(list)
}
inner class MyViewHolder(val binding: RvStateListBinding) :
RecyclerView.ViewHolder(binding.root)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
return MyViewHolder(
RvStateListBinding.inflate(
LayoutInflater.from(parent.context),
parent,
false
)
)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
}
override fun getItemCount(): Int {
return stateList.size
}
}
Submit list using adapter instance
val list = emptyList<State>()
val rvStatesAdapter = RvStatesAdapter()
// init recyclerview properties
rvStatesAdapter.submitList(list)

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])
}

Why does my code not enter this adapter class?

I'm new to Kotlin and Android studio.
I'm trying to get a recycle view to work properly but I'm running into a problem when trying to use an adapter class.
I tried taking a look with breakpoints. but it seems to trigger on the very first line where the class gets defined. ( so class OrganisationsAdapter...etc ) and after that it skips the whole class, it doesnt even enter it.
I also don't get any exceptions.
Adapter Class
class OrganisationsAdapter(
private val myDataset: Array<String>
) : RecyclerView.Adapter<OrganisationsAdapter.MyViewHolder>() {
class MyViewHolder(
val textView: TextView
) : RecyclerView.ViewHolder(textView) {
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
var cell = LayoutInflater.from(parent.context).inflate(R.layout.example_item, parent, false)
val textView = cell.findViewById<TextView>(R.id.organisation_name)
return MyViewHolder(textView)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
holder.textView.text = myDataset[position]
}
override fun getItemCount() = myDataset.size
}
**The line I use to call the class **
recyclerViewOrganisationFragment.adapter = OrganisationsAdapter(Array(getTopics().size) { i -> getTopics()[i].name })

You need to pass the inflated layout to ViewHolder instead of TextView
ex:
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
var cell = LayoutInflater.from(parent.context).inflate(R.layout.example_item, parent, false)
return MyViewHolder(cell)
}
class MyViewHolder(
val itemView: View
) : RecyclerView.ViewHolder(itemView) {
//TODO get textview here itemView.findViewByID
}
Update the viewholder accordingly with textview etc.,

Thank you Lakhwinder.
"You need to pass on ArrayList on the constructor of the adapter, you are passing a size"

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()