SecondFragment.kt

package com.learnpainless.androidnavigation.fragments

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.navigation.fragment.findNavController
import com.learnpainless.androidnavigation.R
import kotlinx.android.synthetic.main.fragment_second.*

class SecondFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false)
    }

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

        //button is id of button in xml file.
        button.setOnClickListener {
            val direction = SecondFragmentDirections.actionSecondFragmentToThirdFragment()
            findNavController().navigate(direction)
        }
    }
}