在Activity中使用VideoSupportFragment触发NullPointerException求助

我在Activity中尝试使用VideoSupportFragment时遇到了NullPointerException，已将该Fragment直接添加到Activity中，但仍触发此错误。唯一能解决问题的方法是将Fragment类型改为普通Fragment，但这样就无法再使用VideoSupportFragment的专属功能。我已将Leanback库版本从1.0.0升级到1.2.0-alpha04。

报错信息 #

FATAL EXCEPTION: main                                                                    
Process: com.example.firstdemotv, PID: 32115

java.lang.NullPointerException: Attempt to invoke virtual method 'androidx.leanback.widget.VerticalGridView androidx.leanback.app.RowsSupportFragment.getVerticalGridView()' on a null object reference
    at androidx.leanback.app.PlaybackSupportFragment.setupChildFragmentLayout(PlaybackSupportFragment.java:780)
    at androidx.leanback.app.PlaybackSupportFragment.onStart(PlaybackSupportFragment.java:955)
    at androidx.fragment.app.Fragment.performStart(Fragment.java:3021)
    at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:589)
    at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:300)
    at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
    at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)

相关代码 #

ListFragment（继承自RowsSupportFragment） #

class ListFragment : RowsSupportFragment() {

private var itemSelectedListener: ((DataModel.Result.Detail) -> Unit)? = null
private var itemClickListener: ((DataModel.Result.Detail) -> Unit)? = null

private val listRowPresenter = object : ListRowPresenter(FocusHighlight.ZOOM_FACTOR_MEDIUM) {
    override fun isUsingDefaultListSelectEffect(): Boolean {
        return false
    }
}.apply {
    shadowEnabled = false
}

private var rootAdapter: ArrayObjectAdapter = ArrayObjectAdapter(listRowPresenter)


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

    adapter = rootAdapter

    onItemViewSelectedListener = ItemViewSelectedListener()
    onItemViewClickedListener = ItemViewClickListener()
}

fun bindData(dataList: DataModel) {

    dataList.result.forEachIndexed { index, result ->
        val arrayObjectAdapter = ArrayObjectAdapter(ItemPresentor())

        result.details.forEach {
            arrayObjectAdapter.add(it)
        }

        val headerItem = HeaderItem(result.title)
        val listRow = ListRow(headerItem, arrayObjectAdapter)
        rootAdapter.add(listRow)

    }

}

fun bindCastData(list: List<CastResponse.Cast>) {
    val arrayObjectAdapter = ArrayObjectAdapter(CastItemPresenter())

    list.forEach { content ->
        arrayObjectAdapter.add(content)
    }

    val headerItem = HeaderItem("Cast & Crew")
    val listRow = ListRow(headerItem, arrayObjectAdapter)
    rootAdapter.add(listRow)}}

调用ListFragment的DetailActivity（继承自FragmentActivity） #

class DetailActivity : FragmentActivity() {

private lateinit var binding: ActivityDetailBinding
lateinit var viewmodel: DetailViewmodel
val castFragment = ListFragment()

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

    binding = DataBindingUtil.setContentView(this, R.layout.activity_detail)

    addFragment(castFragment)

    val movieId = intent.getIntExtra("id", 0)

    val repository = (application as MyApplication).tmdbRepo

    viewmodel = ViewModelProvider(
        owner = this,
        factory = DetailViewmodelFactory(repository, movieId)
    )[DetailViewmodel::class.java]

    viewmodel.movieDetails.observe(this) {

        when (it) {
            is Response.Loading -> {

            }

            is Response.Success -> {
                setData(it.data)
            }

            is Response.Error -> {

            }

            else -> {}
        }

    }

    viewmodel.castDetails.observe(this) {

        when (it) {
            is Response.Loading -> {

            }

            is Response.Success -> {
                if (!it.data?.cast.isNullOrEmpty()) {
                    castFragment.bindCastData(it.data?.cast!!)
                }
            }

            is Response.Error -> {

            }

            else -> {}
        }
    }

    binding.addToMylist.setOnKeyListener { view, keyCode, keyEvent ->
        when (keyCode) {
            KeyEvent.KEYCODE_DPAD_DOWN -> {
                if (keyEvent.action == KeyEvent.ACTION_DOWN) {
                    castFragment.requestFocus()
                }
            }
        }

        false
    }

    binding.play.setOnClickListener {
        val intent = Intent(this@DetailActivity, PlaybackActivity::class.java)
        startActivity(intent)
    }
}

调用ListFragment的HomeFragment（继承自Fragment） #

class HomeFragment : Fragment() {

private lateinit var binding: FragmentHomeBinding
val listFragment = ListFragment()

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View {
    binding = FragmentHomeBinding.inflate(inflater, container, false)
    return binding.root
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val transaction = requireActivity().supportFragmentManager.beginTransaction()
    transaction.add(binding.listFragments.id, listFragment)
    transaction.commit()

    val gson = Gson()
    val i: InputStream = requireContext().assets.open("movies.json")
    val br = BufferedReader(InputStreamReader(i))
    val dataList: DataModel = gson.fromJson(br, DataModel::class.java)

    listFragment.bindData(dataList)
    listFragment.setOnContentSelectedListener {
        updateBanner(it)
    }
    listFragment.setOnItemClickListener {
        val intent = Intent(requireActivity(), DetailActivity::class.java)
        intent.putExtra("id", it.id)
        startActivity(intent)
        requireActivity().finish()
    }

}

内容的提问来源于stack exchange，提问作者LastMomentCoder