android kotlin try with a small app dev

package com.calo.kotlinlanglearning

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.TextView
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {

    private lateinit var txt01: TextView;
    private lateinit var recycler01: RecyclerView;
    private lateinit var dataRepo:ArrayList<recDataSrc>;
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        txt01= findViewById(R.id.txt01)
        recycler01=findViewById(R.id.recycler01);
        recycler01.layoutManager=LinearLayoutManager(this)
        dataRepo=ArrayList()//init an ArrayList
        for (i in 1..20){
            dataRepo.add(recDataSrc("btn"+i, "txt$i"))
        }
        val a: (Int) -> Unit ={ p->onListItemClick(p)}//Unit corresponds to void
        recycler01.adapter=recDataAdapter(dataRepo,a)

    }

    fun btn01_Click(view: View) {
        if(txt01.text.equals(resources.getString(R.string.hello_world))) {//1. getString using the resource.getString method to look up strings resource file
            txt01.setText(R.string.hello_world_CN);
        }else{
            txt01.setText(R.string.hello_world);
        }
        dataRepo.removeLast()
        recycler01.adapter?.notifyDataSetChanged()//this is used to refresh the recyclerview after data change
    }

    private fun onListItemClick(position: Int){//2. method returns Unit which is void replacement
        val cur=dataRepo[position]

        if(txt01.text.equals(resources.getString(R.string.hello_world))) {//1. getString using the resource.getString method to look up strings resource file
            txt01.setText(R.string.hello_world_CN);
        }else{
            txt01.setText(R.string.hello_world);
        }
    }



}

=============main activity above

package com.calo.kotlinlanglearning

import androidx.recyclerview.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.TextView
import android.widget.Toast

class recDataAdapter(private val mList: List<recDataSrc>, private val onItemClick: (position:Int)->Unit) : RecyclerView.Adapter<recDataAdapter.ViewHolder>()  {


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context)
            .inflate(R.layout.reclistitem, parent, false)
        return ViewHolder(view,onItemClick)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {

        val ItemsViewModel = mList[position]

//        holder.imageView.setImageResource(ItemsViewModel.image)

        holder.btn.text=ItemsViewModel.btnText
        holder.textView.text = ItemsViewModel.text

    }

    override fun getItemCount(): Int {
        return mList.size
    }

    class ViewHolder(itemView: View,private val onItemClick: (position:Int)->Unit) : RecyclerView.ViewHolder(itemView),View.OnClickListener  {
        val textView: TextView = itemView.findViewById(R.id.textView)
        val btn: Button=itemView.findViewById(R.id.recitembtn01)


        init {
            itemView.setOnClickListener(this)
            btn.setOnClickListener(this)//4. the btn should bind to a listener currently this one
        }

        override fun onClick(p0: View?) {
            val id=p0?.id
            if(id==R.id.recitembtn01){
                val a=5//3.this is hit when button in the item is clicked
            }
            val position = adapterPosition //5. this still gets the value when the button is clicked
            onItemClick(position)
        }


    }


}

============== recyclerview adapter code above

package com.calo.kotlinlanglearning

data class recDataSrc(val btnText:String,val text:String)
============== recyclerview model code above

Summary:
kotlin is somehow briefer than java, and this recyclerview explore addreses how to use item click, as well as button
cclick event inside of a recycler view item