Defines both the navigation and receiving arguments

RegistrationFragment.kt

class RegistrationFragment : Fragment() {

    private lateinit var bi: FragmentRegistrationBinding
    lateinit var vModel: MainViewModel
    private val flag: RegistrationFragmentArgs by navArgs()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        vModel = activity?.run {
            ViewModelProviders.of(this)[MainViewModel::class.java]
        } ?: throw Exception("Invalid Activity")

    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        bi = FragmentRegistrationBinding.inflate(inflater, container, false)
        bi.callback = this

        return bi.root
    }

    fun BtnStart() {
        if (!Validator.emptyCheckingContainer(layoutInflater.context, bi.fldGrpA))
            return

        // Set Users
        vModel.setUsers(listOf(bi.fName.text.toString(), bi.sName.text.toString()))

        // Navigation
        findNavController().navigate(RegistrationFragmentDirections.actionRegistrationFragmentToFirstFragment())
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        (activity as AppCompatActivity?)!!.supportActionBar!!.hide()
    }

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

        // Get NavArguments
        bi.txtHead.visibility =
            if (flag.welcomeFlag) View.VISIBLE else View.GONE // getting argument data
    }
}