fragment から親の activity を操作する

class TopFragment : Fragment() {
    private lateinit var binding: FragmentTopBinding
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        binding = FragmentTopBinding.inflate(inflater)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // activity で親の activity が取得できる
        val button = activity!!.findViewById<AppCompatButton>(R.id.sampleButton)
    }
}

requireActivity().let {
    if (it is Parent) {
          it.parentMethod()
    }
}