Android的LifeCycleOwner疑问？？

android新手，在用observe的时候遇到这个问题，这里需要实现lifecycleOwner接口的类，androidx.fragment.app.Fragment不是就是实现了这个借口嘛？为什么还会报这个错误呢？求解答

class PlaceFragment : Fragment() {

    val viewModel by lazy { ViewModelProviders.of(this).get(PlaceViewModel::class.java) }

    private lateinit var adapter: PlaceAdapter

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

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        val layoutManager = LinearLayoutManager(activity)
        recyclerView.layoutManager = layoutManager
        adapter = PlaceAdapter(this, viewModel.placeList)
        recyclerView.adapter = adapter
        searchPlaceEdit.addTextChangedListener { editable ->
            val content = editable.toString()
            if (content.isNotEmpty()) {
                viewModel.searchPlaces(content)
            } else {
                recyclerView.visibility = View.GONE
                bgImageView.visibility = View.VISIBLE
                viewModel.placeList.clear()
                adapter.notifyDataSetChanged()
            }
        }
        viewModel.placeLiveData.observe(this, Observer{ result ->
            val places = result.getOrNull()
            if (places != null) {
                recyclerView.visibility = View.VISIBLE
                bgImageView.visibility = View.GONE
                viewModel.placeList.clear()
                viewModel.placeList.addAll(places)
                adapter.notifyDataSetChanged()
            } else {
                Toast.makeText(activity, "未能查询到任何地点", Toast.LENGTH_SHORT).show()
                result.exceptionOrNull()?.printStackTrace()
            }
        })
    }
}

这个是会报错，但是并不影响编译运行。谷歌推荐使用 viewLifecycleOwner ，按照谷歌的走吧，可能影响到了什么生命周期之类的东西。

        mainModel.state.observe(
            viewLifecycleOwner,
            Observer { authenticationState ->
                when (authenticationState) {
                    true -> {
                        showUi()
                    }
                }
            })