在發(fā)帖之前，我花了相當多的時間自己弄清楚，不過我已經(jīng)刪除了各種錯誤。我正在開發(fā)一個小筆記應(yīng)用程序，在我的應(yīng)用程序中使用包含回收視圖的片段之前，一切都很好。問題是我無法將從數(shù)據(jù)庫檢索到的數(shù)據(jù)傳遞給回收視圖適配器。錯誤顯示“嘗試在空對象引用上調(diào)用虛方法‘void com.example.diary.RecyclerAdapter.setdata(java.util.List)’”我已驗證數(shù)據(jù)不為空，我很困惑為什么我會收到空指針錯誤。相關(guān)代碼貼在下面。fragment.java @Overridepublic View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {    view = inflater.inflate(R.layout.fragment_recents, container, false);    RecyclerAdapter adapter;    db = NotesDatabase.createdb(getContext());    adapter = new RecyclerAdapter(numofitems);      retrievetasks();    layoutManager = new LinearLayoutManager(getActivity());    binding = DataBindingUtil.setContentView(getActivity(), R.layout.fragment_recents);    binding.recyclerView.setLayoutManager(layoutManager);    binding.recyclerView.setAdapter(adapter);    Log.d("adapeter", "has set");    return view;}public void retrievetasks() {    try {        LiveData<List<NotesEntry>> notesEntries = db.Dao().loadalltasks();        notesEntries.observe(this, new Observer<List<NotesEntry>>() {            @Override            public void onChanged(List<NotesEntry> notesEntries) {                notes = notesEntries;                Log.d("sizeforall", String.valueOf(notesEntries.size()));                adapter.setdata(notesEntries); //this is where the error occures }             });'adapter.setdata(notesEntries); //這是錯誤發(fā)生的地方'adapter.java public void setdata(List<NotesEntry> notesEntries) {    try {        notesEntryList = notesEntries;        notifyDataSetChanged();    } catch (Exception e) {        e.printStackTrace();    }}public List<NotesEntry> getnotesentries() {    return notesEntryList;}如果我不使用片段，則不會出現(xiàn)此問題。感謝您的幫助。