ViewPager2 + RecyclerView in it items

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val viewPager = findViewById<ViewPager2>(R.id.caradd_viewpager)
        viewPager.adapter = ViewPagerAdapter(viewPager, this)

        this.findViewById<Button>(R.id.caradd_btn_viewpager_back)
                .setOnClickListener{
                    if (viewPager.currentItem !=0) {
                        viewPager.setCurrentItem(viewPager.currentItem-1, true)
                    }
                }
    }
}

/* ======================================================================== */

class ViewPagerAdapter(private val viewpager2: ViewPager2): RecyclerView.Adapter<ViewPagerViewHolder>() {

    private val brands: Array<String> = arrayOf("BMW", "Honda", "Hyundai", "Subaru", "Suzuki")
    private val models: Array<Array<String>> = arrayOf(
        arrayOf("Series 3", "Series 5", "X3", "X5", "GT"),
        arrayOf("Accord", "Civic", "CR-V", "Element", "Pilot"),
        arrayOf("Creta", "Elantra", "ix35", "Santa FE", "Solaris"),
        arrayOf("BRZ", "Forester", "Impreza", "Legacy", "Outback"),
        arrayOf("Grand Vitara", "Jimny", "Kizashi", "Vitara", "Swift")
    )

    private var selectedBrand: Int? = null
    private var selectedMark: Int? = null

    private var recyclerView: RecyclerView? = null
    private var recyclerAdapter: VP_RecyclerViewAdapter? = null

    private val viewAdapter2_pages_count = 2

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewPagerViewHolder {
        val vpItem = LayoutInflater.from(parent.context).inflate(R.layout.caradd_viewpager_item, parent, false)
        return ViewPagerViewHolder(vpItem)
    }

    override fun getItemCount(): Int = viewAdapter2_pages_count

    override fun onBindViewHolder(holder: ViewPagerViewHolder, position: Int) = holder.itemView.run {
        when (position) {
            0 -> {
                // brand select
                caradd_viewpager_header.text = "Select brand"
                reAssingnRecyclerView(holder.itemView, brands, true)
            }
            1 -> {
                // mark select
                caradd_viewpager_header.text = "Select mark"
                reAssingnRecyclerView( holder.itemView, models[selectedBrand!!], false)
            }
            else -> {}
        }
    }


    private fun reAssingnRecyclerView(v: View, myDataset: Array<String>, isIconsShow: Boolean = false){

        recyclerView =
            v.findViewById<RecyclerView>(R.id.caradd_viewpager_recyclerview).apply {
                setHasFixedSize(true)
            }

        val layoutManager = LinearLayoutManager(v.context)
        recyclerView?.layoutManager = layoutManager


        val newRecyclerAdapter = VP_RecyclerViewAdapter(myDataset, isIconsShow) { pos ->
            this@ViewPagerAdapter.selectedBrand = pos
            Log.d("***","ViewPagerAdapter - reAssignRecyclerView - " + this.selectedBrand)
            viewpager2.setCurrentItem(viewpager2.currentItem + 1, true)
        }

        // specify an viewAdapter
        if (recyclerAdapter==null) {
            recyclerAdapter = newRecyclerAdapter
            recyclerView!!.adapter = recyclerAdapter
        } else {
            recyclerAdapter?.clear()
            recyclerView!!.swapAdapter(newRecyclerAdapter, true)
            recyclerAdapter = newRecyclerAdapter
        }
    }

}


/* ======================================================================== */


class ViewPagerViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)


/* ======================================================================== */


class VP_RecyclerViewAdapter(
    private var dataset: Array<String>,
    private val isIconShow: Boolean,
    private val lambdaFun: (Int) -> Unit
): RecyclerView.Adapter<VP_RecyclerViewViewHolder>() {
    override fun onCreateViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): VP_RecyclerViewViewHolder {
        val rvItem = LayoutInflater.from(parent.context).inflate(R.layout.caradd_viewpager_item_recyclerview_item, parent, false)
        return VP_RecyclerViewViewHolder(rvItem)
    }


    fun clear() {
        val size: Int = dataset.size
        if (size > 0) {
            for (i in 0 until size) {
                dataset.drop(i)
            }
            notifyItemRangeRemoved(0, size)

        }
        notifyDataSetChanged()
    }


    override fun onBindViewHolder(holder: VP_RecyclerViewViewHolder, position: Int) {
        holder.textView.findViewById<TextView>(R.id.caradd_viewpager_item_recyclerview_item_text).text = dataset[position]
        holder.itemView.setOnClickListener {
            Log.d("***", "position selected $position")
            this.lambdaFun(position)
        }
    }

    override fun getItemCount() = dataset.size

}


/* ======================================================================== */


class VP_RecyclerViewViewHolder(val textView: View) : RecyclerView.ViewHolder(textView)