缺少必需的参数“名称”并且没有 android:defaultValue

Question

我的代码有问题，我试图在片段之间传递参数，但java.lang.IllegalArgumentException: Required argument "name" is missing and does not have an android:defaultValue在运行时出现异常 。我仍然是初学者，所以我无法真正说出问题的来源。

class ListNotesFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        val binding = DataBindingUtil.inflate<FragmentListNotesBinding>(inflater, R.layout.fragment_list_notes, container, false)

        val application = requireNotNull(this.activity).application

        val args = ListNotesFragmentArgs.fromBundle(arguments!!).name

        val dataSource = NoteDatabase.getInstance(application).noteDatabaseDao

        val viewModelFactory = ListNoteViewModelFactory(args, dataSource)

        val listNoteViewModel = ViewModelProviders.of(this, viewModelFactory).get(ListNoteViewModel::class.java)

        binding.listNoteViewModel = listNoteViewModel

        binding.lifecycleOwner = this

        binding.addButton.setOnClickListener{
            this.findNavController().navigate(R.id.action_listNotesFragment_to_detailNoteFragment)
        }

        listNoteViewModel.navigateToDetailNoteFragment.observe(viewLifecycleOwner, Observer{
            it?.let {
                this.findNavController().navigate(ListNotesFragmentDirections
                    .actionListNotesFragmentToDetailNoteFragment(it.noteId))

                listNoteViewModel.doneNavigating()
            }
        })

        return binding.root
    }

}

Answer 1

所以你的问题是这一行：

val args = ListNotesFragmentArgs.fromBundle(arguments!!).name

当它为空时保护自己的方法是在你的 nav_graph.xml 参数中设置一个defaultValue，它看起来像这样：

<argument
    android:name="name"
    app:argType="string"
    app:nullable="true"
    android:defaultValue="@null"/>