NestedScrollView + Paginated Recyclerview Android

DataFragment.kt

import android.os.Bundle
import android.view.View
import android.view.ViewGroup
import androidx.core.view.ViewCompat
import androidx.core.widget.NestedScrollView
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.RecyclerView
import kotlinx.android.synthetic.main.fragment_data.nsvData
import kotlinx.android.synthetic.main.fragment_data.rvData

class DataFragment : Fragment() {

  override fun onViewCreated(
    view: View,
    savedInstanceState: Bundle?
  ) {
    super.onViewCreated(view, savedInstanceState)

    enablePagination(
        nestedScrollView = nsvData,
        recyclerView = rvData,
        nextPageFunction = viewModel::fetchNextData
    )
  }

  private var paginatedRV: RecyclerView? = null
  private fun enablePagination(
    nestedScrollView: NestedScrollView,
    recyclerView: RecyclerView,
    nextPageFunction: () -> Unit
  ) {
    //Disable nested recyclerview from scrolling
    ViewCompat.setNestedScrollingEnabled(recyclerView, false)
    //Attach scroll listener to nested scrollview
    nestedScrollView.viewTreeObserver?.addOnScrollChangedListener {
      //If the paginated rv is not calculated already
      if (paginatedRV == null) {
        //Get the parent holder
        val holder = nestedScrollView.getChildAt(0) as ViewGroup
        //Loop through all children of parent holder
        for (i in 0 until holder.childCount) {
          //Pull the pagination recyclerview child
          if (holder.getChildAt(i).id == recyclerView.id) {
            paginatedRV = holder.getChildAt(i) as RecyclerView
            break
          }
        }
      }
      paginatedRV?.let {
        //Identify if recyclerview is scrolled to bottom
        if (it.bottom - (nestedScrollView.height + nestedScrollView.scrollY) == 0)
          nextPageFunction()
      }
    }
  }

}

fragment_data.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/background_color"
    android:orientation="vertical"
    tools:context="com.karntrehan.DataFragment"
    >

  <include layout="@layout/toolbar"/>

  <androidx.core.widget.NestedScrollView
      android:id="@+id/nsvData"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginLeft="8dp"
      android:layout_marginRight="8dp"
      tools:visibility="visible"
      >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        >

      <Button
          android:id="@+id/btnViewed"
          android:layout_width="wrap_content"
          android:layout_height="36dp"
          android:layout_gravity="end|right"
          android:layout_marginTop="16dp"
          android:background="@color/white"
          android:padding="8dp"
          android:text="@string/viewed"
          android:textColor="@color/recently_viewed_text_color"
          android:textSize="12sp"
          style="@style/Button.Flat"
          />

      <TextView
          android:id="@+id/tvDataCount"
          android:layout_height="match_parent"
          android:layout_marginBottom="8dp"
          android:textColor="@color/text_color_primary"
          tools:text="Showing 248 Events"
          style="@style/Text.Title.Regular"
          />

      <androidx.recyclerview.widget.RecyclerView
          android:id="@+id/rvData"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical"
          app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
          tools:itemCount="3"
          tools:listitem="@layout/item_data"
          />


      <ProgressBar
          android:id="@+id/pbLoading"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="center"
          android:layout_margin="8dp"
          style="?android:attr/progressBarStyle"
          />

    </LinearLayout>

  </androidx.core.widget.NestedScrollView>

  <include
      layout="@layout/layout_empty"
      android:id="@+id/noData"
      android:layout_width="match_parent"
      android:layout_height="0dp"
      android:layout_weight="1"
      android:visibility="gone"
      tools:visibility="gone"
      />

</LinearLayout>

please help in explaining nextPageFunction = viewModel::fetchNextData this view model function