Steps to create viewpager in kotlin

tab_fragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.lifecycle.ViewModelProviders
import com.app.base.R
import kotlinx.android.synthetic.main.referral_fragment.*

class ReferralFragment : Fragment() {

    companion object {
        fun newInstance() = ReferralFragment()
    }

    private lateinit var viewModel: ReferralViewModel

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.tab_fragment, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProviders.of(this).get(ReferralViewModel::class.java)

        val adapter = ViewPagerAdapter(this.fragmentManager!!)
        adapter.addFragment(Tab1Fragment(), "tab1")
        adapter.addFragment(Tab2Fragment(), "tab2")
        viewPager.adapter = adapter
        tabs.setupWithViewPager(viewPager)
    }

}

tab_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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/colorWhite"
    tools:context="com.app.base.ui.dashboard.referral.ReferralFragment">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabs"

        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/new_referral" />

        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/existing_referral" />

    </com.google.android.material.tabs.TabLayout>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tabs">

    </androidx.viewpager.widget.ViewPager>

</androidx.constraintlayout.widget.ConstraintLayout>

ViewPagerAdapter.kt

import android.annotation.SuppressLint
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentPagerAdapter
import androidx.fragment.app.FragmentStatePagerAdapter

@SuppressLint("WrongConstant")
class ViewPagerAdapter(supportFragmentManager: FragmentManager) : FragmentStatePagerAdapter(supportFragmentManager, FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
    private val mFragmentList = ArrayList<Fragment>()
    private val mFragmentTitleList = ArrayList<String>()

    override fun getItem(position: Int): Fragment {
        return mFragmentList[position]
    }

    override fun getCount(): Int {
        return mFragmentList.size
    }

    override fun getPageTitle(position: Int): CharSequence? {
        return mFragmentTitleList[position]
    }

    fun addFragment(fragment: Fragment, title: String) {
        mFragmentList.add(fragment)
        mFragmentTitleList.add(title)
    }