刷新 RecycleView 的 ListAdapter 的问题

Question

我正在尝试观察 Mu​​tableLiveData 并刷新 RecycleView，但它不起作用。这是我的片段代码：

class NowyZestaw : Fragment() {

    val setEditModeViewModel: SetEditModeViewModel by activityViewModels()
    


    @VisibleForTesting(otherwise = VisibleForTesting.PRIVATE)
    val bazaModel: BazaModel by activityViewModels()

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val root = inflater.inflate(R.layout.nowy_zestaw, container, false)
        root.findViewById<RecyclerView>(R.id.flashcard_recycler).isNestedScrollingEnabled = false
        return root
    }

    @SuppressLint("ShowToast")
    override fun onViewCreated(root: View, savedInstanceState: Bundle?) {
        val addFlashcard: Button = root.findViewById(R.id.dodajFiszke)
        addFlashcard.setOnClickListener {
            val fiszka = Fiszka(0, "test", "test", 1)
//            bazaModel.dodajFiszke(fiszka)
            setEditModeViewModel.addNewFlashcard(Fiszka(1, "raz", "raz", 1))
        }

        val recyclerView: RecyclerView = root.findViewById(R.id.flashcard_recycler)
        recyclerView.layoutManager = LinearLayoutManager(root.context)

        val adapter = SetAdapter()
        recyclerView.adapter = adapter

        setEditModeViewModel.flashcards.observe(viewLifecycleOwner, Observer { flashcardList ->
            Log.d("ANDROID", flashcardList.size.toString())
            adapter.submitList(flashcardList)
        })
    }
}

这是我的视图模型：

class SetEditModeViewModel : ViewModel() {

    val flashcards = MutableLiveData<MutableList<Fiszka>>().apply {
        value = mutableListOf()
    }

    fun addNewFlashcard(item: Fiszka) {
        flashcards.value?.add(item)
        flashcards.value = flashcards.value
    }
}

和 xml 行：

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <androidx.recyclerview.widget.RecyclerView
                android:id="@+id/flashcard_recycler"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                tools:listitem="@layout/nowa_fiszka" />

        </RelativeLayout>

当我单击控制台中的按钮时，会显示正确的列表大小，因此这意味着已通知观察到。例如，当我更改智能手机方向时，项目会出现在回收视图中。更重要的是，如果我观察 Room 数据库，返回 LiveData 一切正常。也许它只适用于 LiveData，不适用于 MutableLiveData，但我不知道它为什么会发生。总而言之，我希望在单击按钮后在 RecyclerView 中出现新项目。有人可以帮我解决这个问题吗？

Answer 1

在你的观察者中你应该调用 notifyDataSetChanged();

    setEditModeViewModel.flashcards.observe(viewLifecycleOwner, Observer { flashcardList ->
        Log.d("ANDROID", flashcardList.size.toString())
        adapter.submitList(flashcardList)
        adapter.notifyDataSetChanged();  // This is needed
    })