GetArguments.kt

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

  arguments?.let {
     val args = MessageListFragmentArgs.fromBundle(it)
     val userId = args.userId
  }
  
  ...  

}

GetArgumentsKTX.kt

val args: MessageListFragmentArgs by navArgs() // if you are using KTX (add -ktx at the end of dependencies)

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
  
  val userId = args.userId
  
  ...  
  
}